Kegg Pathway: TGF-beta signaling pathway

J Immunol. 2009 Nov 18;
Han L, Wang W, Fang Y, Feng Z, Liao S, Li W, Li Y, Li C, Maitituoheti M, Dong H, Lai Z, Gao Q, Xi L, Wu M, Wang D, Zhou J, Meng L, Wang S, Ma D

B and T lymphocyte attenuator (BTLA)-herpesvirus entry mediator (HVEM) signaling coinhibitory pathway is believed to impair antitumor immune competences. An intriguing unresolved question is whether blockade of BTLA-HVEM guides an effective therapeutic tool against established tumors. To address this issue, we constructed a eukaryotic expression plasmid (psBTLA) that expressed the extracellular domain of murine BTLA (soluble form of BTLA), which could bind HVEM, the ligand of BTLA, and block BTLA-HVEM interactions. The data in this study showed that treatment by injection of psBTLA resulted in down-regulation of IL-10 and TGF-beta and promotion of dendritic cell function by increasing the expression of B7-1 and IL-12, but the adaptive antitumor immune responses achieved by psBTLA administration alone were limited and could not eradicate the tumor effectively. Next, we evaluated the immunotherapeutic efficacy and mechanism of combination therapy of heat shock protein 70 (HSP70) vaccine/psBTLA by using murine TC-1 cervical cancer mice as an ectopic tumor model. Our in vivo studies revealed that treatment with HSP70 vaccine alone did not lead to satisfactory tumor growth inhibition, whereas cotreatment with psBTLA significantly improved antitumor immunity and compensated the deficiency of HSP70 vaccine by increasing the expression of Th1 cytokines, IL-2, and IFN-gamma and decreasing transcription levels of IL-10, TGF-beta, and Foxp3 in the tumor microenvironment. Taken together, our findings indicate that blocking the BTLA-HVEM interaction with sBTLA enhances antitumor efficacy and results in a significant synergistic effect against existent tumor cells in vivo when combined with the HSP70 vaccine.

Circ Heart Fail. 2009 Nov 1; 2(6): 633-642
Divakaran V, Adrogue J, Ishiyama M, Entman ML, Haudek S, Sivasubramanian N, Mann DL

BACKGROUND: Previous studies suggest that transforming growth factor-beta provokes cardiac hypertrophy and myocardial fibrosis; however, it is unclear whether the deleterious effects of transforming growth factor-beta signaling are conveyed through SMAD-dependent or SMAD-independent signaling pathways. METHODS AND RESULTS: To determine the contribution of SMAD-dependent signaling to cardiac remodeling, we performed transaortic constriction in SMAD3 null (SMAD3(-/-)) and littermate control mice (age, 10 to 12 weeks). Cumulative survival 20 days after transaortic constriction was significantly less in the SMAD3(-/-) mice when compared with littermate controls (43.6% versus 90.9%, P<0.01). Transaortic constriction resulted in a significant increase in cardiac hypertrophy in the SMAD3(-/-) mice, denoted by an increase in the heart weight to tibial length ratio and increased myocyte cross-sectional area. Loss of SMAD3 signaling also resulted in a significant 60% decrease in myocardial fibrosis (P<0.05). A microRNA microarray showed that 55 microRNAs were differentially expressed in littermate and SMAD3(-/-) mice and that 10 of these microRNAs were predicted to bind to genes that regulate the extracellular matrix. Of these 10 candidate microRNAs, both miR-25 and miR-29a were sufficient to decrease collagen gene expression when transfected into isolated cardiac fibroblasts in vitro. CONCLUSIONS: The results suggest that SMAD3 signaling plays dual roles in the heart: one beneficial role by delimiting hypertrophic growth and the other deleterious by modulating myocardial fibrosis, possibly through a pathway that entails accumulation of microRNAs that decrease collagen gene expression.

J Cell Physiol. 2009 Nov 13;
Ishibashi O, Ikegame M, Takizawa F, Yoshizawa T, Moksed MA, Iizawa F, Mera H, Matsuda A, Kawashima H

The periodontal ligament (PDL), a connective tissue located between the cementum of teeth and the alveolar bone of mandibula, plays a crucial role in the maintenance and regeneration of periodontal tissues. The PDL contains fibroblastic cells of a heterogeneous cell population, from which we have established several cell lines previously. To analyze characteristics unique for PDL at a molecular level, we performed cDNA microarray analysis of the PDL cells versus MC3T3-E1 osteoblastic cells. The analysis followed by validation by reverse transcription-polymerase chain reaction and immunochemical staining revealed that endoglin, which had been shown to associate with transforming growth factor (TGF)-beta and bone morphogenetic proteins (BMPs) as signaling modulators, was abundantly expressed in PDL cells but absent in osteoblastic cells. The knockdown of endoglin greatly suppressed the BMP-2-induced osteoblastic differentiation of PDL cells and subsequent mineralization. Interestingly, the endoglin knockdown did not alter the level of Smad-1/5/8 phosphorylation induced by BMP-2, while it suppressed the BMP-2-induced expression of Id1, a representative BMP-responsive gene. Therefore, it is conceivable that endoglin regulates the expression of BMP-2-responsive genes in PDL cells at some site downstream of Smad-1/5/8 phosphorylation. Alternatively, we found that Smad-2 as well as Smad-1/5/8 was phosphorylated by BMP-2 in the PDL cells, and that the BMP-2-induced Smad-2 phosphorylation was suppressed by the endoglin knockdown. These results, taken together, raise a possibility that PDL cells respond to BMP-2 via a unique signaling pathway dependent on endoglin, which is involved in the osteoblastic differentiation and mineralization of the cells. J. Cell. Physiol. (c) 2009 Wiley-Liss, Inc.

Mol Cell. 2009 Nov 13; 36(3): 457-68
Gao S, Alarcón C, Sapkota G, Rahman S, Chen PY, Goerner N, Macias MJ, Erdjument-Bromage H, Tempst P, Massagué J

TGF-beta induces phosphorylation of the transcription factors Smad2 and Smad3 at the C terminus as well as at an interdomain linker region. TGF-beta-induced linker phosphorylation marks the activated Smad proteins for proteasome-mediated destruction. Here, we identify Nedd4L as the ubiquitin ligase responsible for this step. Through its WW domain, Nedd4L specifically recognizes a TGF-beta-induced phosphoThr-ProTyr motif in the linker region, resulting in Smad2/3 polyubiquitination and degradation. Nedd4L is not interchangeable with Smurf1, a ubiquitin ligase that targets BMP-activated, linker-phosphorylated Smad1. Nedd4L limits the half-life of TGF-beta-activated Smads and restricts the amplitude and duration of TGF-beta gene responses, and in mouse embryonic stem cells, it limits the induction of mesoendodermal fates by Smad2/3-activating factors. Hierarchical regulation is provided by SGK1, which phosphorylates Nedd4L to prevent binding of Smad2/3. Previously identified as a regulator of renal sodium channels, Nedd4L is shown here to play a broader role as a general modulator of Smad turnover during TGF-beta signal transduction.

J Immunotoxicol. 2009 Nov 16;
Kelly RJ, Morris JC

Transforming growth factor-beta (TGF-beta) is a pleiotropic growth factor that regulates cell growth and differentiation, apoptosis, cell motility, extracellular matrix production, angiogenesis, and cellular immune responses. TGF-beta demonstrates paradoxical action whereby it can function to suppress early tumorigenesis; however, it can also facilitate malignant transformation and stimulate tumor growth by manipulating a more hospitable environment for tumor invasion and the development of metastases. Given the integral role of TGF-beta in transformation and cancer progression, various components of the TGF-beta signaling pathway offer potentially attractive therapeutic targets for cancer treatment. This review focuses on the role of TGF-beta in cancer and discusses both small and large molecule drugs currently in development that target TGF-beta, its receptor and important down stream steps along its signaling pathway.

J Hepatol. 2009 Oct 24;
Kao YH, Chen CL, Jawan B, Chung YH, Sun CK, Kuo SM, Hu TH, Lin YC, Chan HH, Cheng KH, Wu DC, Goto S, Cheng YF, Chao D, Tai MH

BACKGROUND & AIMS: Hepatoma-derived growth factor (HDGF) expression is correlated with progression of hepatocellular carcinoma. Since liver fibrosis frequently occurs before hepatoma development, this study investigated the expression profile of HDGF and its relationship with transforming growth factor-beta (TGF-beta signaling in experimental models of hepatofibrogenesis. METHODS: Liver fibrosis was induced in mice receiving bile duct ligation (BDL) or carbon tetrachloride (CCl(4)) administration. The expression levels of HDGF and other fibrosis-related markers were measured using quantitative RT-PCR, Western blotting, and enzyme-linked immunosorbent assays. Hepatic HDGF overexpression was achieved by adenovirus gene delivery. Rat hepatocytes were used to study the interplay between HDGF and TGF-beta1. RESULTS: In both liver fibrosis models, HDGF de novo synthesis significantly increased during the progression of fibrosis. The HDGF upregulation was observed mainly in hepatocytes and correlated with the expression of TGF-beta1 and collagen COL1A1 and COL1A2 proteins. Hepatic HDGF overexpression itself deteriorated hepatocellular structure and integrity, and aggravated the extents of BDL- and CCl(4)-induced liver fibrosis with concomitant upregulation of TGF-beta1 and COL1A1. Exogenous TGF-beta1 stimulated HDGF expression only in cultured primary hepatocytes grown on collagen matrix, whereas exogenous HDGF also increased TGF-beta1 production in hepatocytes in a collagen-dependent manner. Moreover, HDGF enhanced Smad2 phosphorylation dose-dependently and the TGF-beta1-driven luciferase activities. CONCLUSION: HDGF plays a pro-fibrogenic role during liver fibrosis in mice through activation of TGF-beta pathway. The mutual regulation between TGF-beta1 and HDGF may facilitate a vicious cycle to promote the progression of hepatic fibrogenesis.

Food Chem Toxicol. 2009 Nov 10;
Jung KJ, Kim J, Park YK, Yoon YR, Park KM

Kidney fibrosis results in chronic renal disease. The current treatment of chronic renal diseases is limited to angiotensin converting enzyme inhibitors and angiotensin receptor blockers. Recently, we found that Wen-pi-tang-Hab-Wu-ling-san (WHW) extract, which has been used to treat renal diseases in herbal medicine for a long time, plays antifibrogenic. Here, we investigated the role of WHW in the kidney fibrosis induced by unilateral ureteral obstruction (UUO) in mice. C57BL/6 male mice were subjected to UUO on day 0 and then administered with either WHW (2, 10, or 50 mg/kg of body weight) or vehicle orally from 1 day after UUO to finish the experiment. WHW administration significantly mitigated the UUO-induced kidney fibrotic changes including tubular atrophy and dilatation, collagen accumulation, expansion of interstitial space and leukocyte infiltration. WHW prevented the increases of oxidative stress by the prevention of UUO-induced decreases of catalase, copper-zinc superoxide dismutase (CuZnSOD) and manganese superoxide dismutase (MnSOD), resulting in reduced production of oxidative stress. Furthermore, WHW reduced transforming growth factor-beta (TGF-beta) expression and phosphorylation of Smad2/3 stimulated by UUO. In conclusion, WHW prevented kidney fibrosis following UUO by the inhibition of inflammation, oxidative stress and TGF-beta/Smad2/3 signaling pathway.

J Vet Intern Med. 2009 Nov 11;
Oyama MA, Levy RJ

Little is known about the molecular abnormalities associated with canine degenerative mitral valve disease (DMVD). The pathology of DMVD involves the differentiation and activation of the normally quiescent mitral valvular interstitial cell (VIC) into a more active myofibroblast phenotype, which mediates many of the histological and molecular changes in affected the valve tissue. In both humans and experimental animal models, increased serotonin (5-hydroxytryptamine, 5HT) signaling can induce VIC differentiation and myxomatous valve damage. In canine DMVD, numerous lines of evidence suggest that 5HT and related molecules such as transforming growth factor-beta play a critical role in the pathogenesis of this disease. A variety of investigative techniques, including gene expression, immunohistochemistry, protein blotting, and cell culture, shed light on the potential role of 5HT in the differentiation of VIC, elaboration of myxomatous extracellular matrix components, and activation of mitogen-activated protein kinase pathways. These studies help support a hypothesis that 5HT and its related pathways serve as an important stimulus in canine DMVD. This review describes the pathological characteristics of canine DMVD, the organization and role of the 5HT pathway in valve tissue, involvement of 5HT in human and experimental models of valve disease, avenues of evidence that suggest a role for 5HT in naturally occurring DMVD, and finally, a overarching hypothesis describing a potential role for 5HT in canine DMVD.

Cell Physiol Biochem. 2009; 24(5-6): 627-34
Tossidou I, Starker G, Kruger J, Meier M, Leitges M, Haller H, Schiffer M

BACKGROUND: Progressive loss of podocytes has been documented as an early lesion in the development of glomerular disease. In a variety of glomerular diseases, including diabetic nephropathy the activation of transforming growth factor-beta (TGF-beta) has been demonstrated to promote podocyte death and the development of glomerulosclerosis. In this manuscript we analyzed the role of PKC-alpha (PKCalpha) on TGF-beta1 induced apoptosis in podocytes. METHODS: To accomplish this we generated stable murine PKCalpha deficient podocyte cell lines and examined survival- and pro-apoptotic signaling signatures as well as caspase activation after stimulation with TGF-beta. RESULTS: After stimulation with TGF-beta we can demonstrate an enhanced and prolonged activation of PI3K/AKT and ERK1/2 in PKCalpha-knockout (PKCalpha-/-) podocytes compared to PKCalpha-wildtype (PKCalpha+/ +) podocytes, whereas proapoptotic signaling via p38MAPK is significantly reduced. Interestingly, activation of the Smad-pathway is also prolonged in the PKCalpha-/-podocytes. When we analyzed the underlying mechanisms we found a TGF-beta inducible interaction of PKCalpha with the TGF-beta-type-I-receptor (TGFbetaRI). Moreover, endocytosis assays showed that the TGFbetaRI is less internalized in PKCalpha-/- podocytes. CONCLUSION: Since we can demonstrate a key role for PKCalpha in the signaling response after stimulation with TGF-beta we conclude that PKCalpha might be an interesting target molecule as a "podocyte protective" therapy.

Mol Hum Reprod. 2009 Nov 11;
Pan Q, Luo X, Chegini N

Aberrant expression of microRNAs (miRNAs), including miR-21, and alteration of their target genes stability, have been associated with cellular transformation and tumorigenesis. We investigated the expression, regulation, and function of miR-21 in leiomyomas which develop from myometrial cellular transformation. The results indicated that miR-21 is overexpressed in leiomyomas with specific elevation during the secretory phase of the menstrual cycle, and in women who received Depo-Provera and oral contraceptives (OCPs), but reduced due to GnRHa therapy (P<0.05). Bioinformatic analysis of microarray gene expression profiles previously obtained from the above cohorts, and myometrial and leiomyoma smooth muscle cells (MSMC and LSMC) treated with GnRHa, TGF-beta and TGF-beta receptor type II (TGF-betaRII) antisense oligomer, indicated that a number of miR-21 predicted target genes were co-expressed and differentially regulated in these cohorts. Gain- and loss-of function of miR-21 in MSMC, LSMC, transformed LSMC (t-LSMC) and leiomyosarcoma cell line (SKLM-S1) resulted in differential expression of many genes, including some of the miR-21 predicted/validated target genes, PTEN, PDCD4 and E2F1, and TGF-betaRII, in cell-specific manner. Gain-of miR-21 function in MSMC and LSMC reduced TGF-beta-induced expression of fibromodulin and TGIF (P<0.05), and moderately altered the rate of cell growth and caspase 3/7 activity in these cells. We concluded that miR-21 is aberrantly expressed and hormonally regulated in leiomyomas where, through functional interaction with ovarian steroids and the TGF-beta signaling pathway, either directly or indirectly regulates a number of genes whose products are critical in leiomyoma growth and regression as well as their potential cellular transformation.

FASEB J. 2009 Nov 11;
Gosens R, Baarsma HA, Heijink IH, Oenema TA, Halayko AJ, Meurs H, Schmidt M

beta-Catenin is a component of adherens junctions that also acts as a transcriptional coactivator when expressed in the nucleus. Growth factors are believed to regulate the nuclear expression of beta-catenin via inactivation of glycogen synthase kinase 3 (GSK-3) by phosphorylation, resulting in increased beta-catenin protein stability. Here, we report on a novel pathway that regulates the expression and nuclear presence of beta-catenin. In proliferating human airway smooth muscle cells, we observed increased expression of beta-catenin, which was required for proliferation. Interestingly, increased beta-catenin expression was accompanied by an increase in beta-catenin mRNA and was independent of beta-catenin liberation from the plasma membrane, suggesting a role for de novo synthesis. This was confirmed using actinomycin D and cycloheximide, which abrogated the induction and nuclear localization of beta-catenin protein. GSK-3 inhibition using SB216763 failed to regulate beta-catenin mRNA. However, expression of dominant negative H-Ras or pharmacological inhibition of MEK reduced serum and TGF-beta-induced beta-catenin mRNA and protein. Collectively, these data indicate that beta-catenin is an important signaling intermediate in airway smooth muscle growth and that its cellular accumulation and nuclear localization require de novo protein synthesis effected, in part, via H-Ras and MEK.-Gosens, R., Baarsma, H. A., Heijink, I. H., Oenema, T. A., Halayko, A. J., Meurs, H., Schmidt, M. De novo synthesis of beta-catenin via H-Ras and MEK regulates airway smooth muscle growth.

Cancer Res. 2009 Nov 10;
Kiyono K, Suzuki HI, Matsuyama H, Morishita Y, Komuro A, Kano MR, Sugimoto K, Miyazono K

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that regulates cell growth, differentiation, and apoptosis of various types of cells. Autophagy is emerging as a critical response of normal and cancer cells to environmental changes, but the relationship between TGF-beta signaling and autophagy has been poorly understood. Here, we showed that TGF-beta activates autophagy in human hepatocellular carcinoma cell lines. TGF-beta induced accumulation of autophagosomes and conversion of microtubule-associated protein 1 light chain 3 and enhanced the degradation rate of long-lived proteins. TGF-beta increased the mRNA expression levels of BECLIN1, ATG5, ATG7, and death-associated protein kinase (DAPK). Knockdown of Smad2/3, Smad4, or DAPK, or inhibition of c-Jun NH(2)-terminal kinase, attenuated TGF-beta-induced autophagy, indicating the involvement of both Smad and non-Smad pathway(s). TGF-beta activated autophagy earlier than execution of apoptosis (6-12 versus 48 h), and reduction of autophagy genes by small interfering RNA attenuated TGF-beta-mediated growth inhibition and induction of proapoptotic genes Bim and Bmf, suggesting the contribution of autophagy pathway to the growth-inhibitory effect of TGF-beta. Additionally, TGF-beta also induced autophagy in some mammary carcinoma cells, including MDA-MB-231 cells. These findings show that TGF-beta signaling pathway activates autophagy in certain human cancer cells and that induction of autophagy is a novel aspect of biological functions of TGF-beta. [Cancer Res 2009;69(23):OF1-9].

Cold Spring Harb Symp Quant Biol. 2009 Nov 10;
Richards GS, Degnan BM

Intercellular signaling underpins metazoan development by mediating the induction, organization, and cooperation of cells, tissues, and organs. Herein, the origins of the four major signaling pathways used during animal development and differentiation-Wnt, Notch, transforming growth factor-beta (TGF-beta), and Hedgehog-are assessed by comparative analysis of genomes from bilaterians, early branching metazoan phyla (poriferans, placozoans, and cnidarians), and the holozoan sister clade to the animal kingdom, the choanoflagellates. On the basis of the incidence and domain architectures of core pathway ligands, receptors, signal transducers, and transcription factors in representative species of these lineages, it appears that the Notch, Wnt, and TGF-beta pathways are metazoan synapomorphies, whereas the Hedgehog pathway arose in the protoeumetazoan lineage, after its divergence from poriferan and placozoan lineages. Examination of the binding domains and motifs present in signaling pathway components of nonbilaterians reveals cases in which signaling interactions are unlikely to be operating in accordance with bilaterian canons. Overall, this study highlights the stability and antiquity of the core cytosolic components of each pathway, juxtaposed with the more variable and recently evolved molecular interactions taking place at the cell surface.

Cancer Biol Ther. 2009 Sep; 8(18): 1691-8
Yao Z, Mishra L

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide, with a median survival of 6-16 m. Factors responsible for the poor prognosis include late onset diagnosis, underlying cirrhosis and resistance to chemotherapy; 40% of HCCs are clonal and therefore potentially arise from progenitor/stem cells. New insights are provided from several signaling pathways, such as STAT3, NOTCH, hedgehog and transforming growth factor-beta (TGFbeta), which are involved in stem cell renewal, differentiation, survival, and are commonly deregulated in HCC. Control of stem cell proliferation by the TGFbeta, Notch, Wnt and Hedgehog pathways to suppress hepatocellular cancer and to form the endoderm suggest a dual role for this pathway in tumor suppression as well as progression of differentiation from a stem or progenitor stage. This review provides a rationale for detecting and analyzing tumor stem cells as one of the most effective ways to treat cancers such as hepatocellular cancer.

Curr Eye Res. 2009 Aug; 34(8): 652-9
Kanno C, Kashiwagi Y, Horie K, Inomata M, Yamamoto T, Kitanaka C, Yamashita H

PURPOSE: Activin is a member of the transforming growth factor-beta (TGF-beta) superfamily and exerts certain effects on differentiation and apoptosis. We investigated the effects of activin on retinoblastoma cell line. MATERIALS AND METHODS: We used retinoblastoma cell line Y79. Intracellular signal transduction of activin was investigated with RT-PCR, immunofluorescence study, and luciferase reporter assay. The effect of activin on cell growth was examined with fluorescence cell viability assays. To determine the effect of activin on apoptosis, a TUNEL assay and an immunofluorescence study of cleaved PARP were performed. The effect of activin on cell differentiation was examined with RT-PCR and Western blotting. RESULTS: Intracellular signal transduction of activin was confirmed in Y79 cells. Activin inhibited Y79 cell growth. Activin induced the expression of neural retina leucine zipper (Nrl) at the mRNA and protein levels. CONCLUSIONS: Nrl is a specific gene in rod photoreceptor development and is a gene indispensable to differentiation into rod photoreceptors, so the present results suggest that activin affects the differentiation of retinoblastoma cells into rod photoreceptor cells.

Can J Physiol Pharmacol. 2009 Oct; 87(10): 764-72
Cunnington RH, Nazari M, Dixon IM

Recent studies demonstrate the critical role of the extracellular matrix in the organization of parenchymal cells in the heart. Thus, an understanding of the modes of regulation of matrix production by cardiac myofibroblasts is essential. Transforming growth factor beta (TGF-beta) signaling is transduced through the canonical Smad pathway, and the involvement of this pathway in matrix synthesis and other processes requires precise control. Inhibition of Smad signaling may be achieved at the receptor level through the targeting of the TGF-beta type I receptors with an inhibitory Smad7 / Smurf2 complex, or at the transcriptional level through c-Ski / receptor-Smad / co-mediator Smad4 interactions. Conversely, Arkadia protein intensifies TGF-beta-induced effects by marking c-Ski and inhibitory Smad7 for destruction. The study of these TGF-beta mediators is essential for future treatment of fibrotic disease, and this review highlights recent relevant findings that may impact our understanding of cardiac fibrosis.

Cell Stem Cell. 2009 Nov 6; 5(5): 504-14
Ikushima H, Todo T, Ino Y, Takahashi M, Miyazawa K, Miyazono K

Despite aggressive surgery, radiotherapy, and chemotherapy, treatment of malignant glioma remains formidable. Although the concept of cancer stem cells reveals a new framework of cancer therapeutic strategies against malignant glioma, it remains unclear how glioma stem cells could be eradicated. Here, we demonstrate that autocrine TGF-beta signaling plays an essential role in retention of stemness of glioma-initiating cells (GICs) and describe the underlying mechanism for it. TGF-beta-induced expression of Sox2, a stemness gene, and this induction was mediated by Sox4, a direct TGF-beta target gene. Inhibitors of TGF-beta signaling drastically deprived tumorigenicity of GICs by promoting their differentiation, and these effects were attenuated in GICs transduced with Sox2 or Sox4. Furthermore, GICs pretreated with TGF-beta signaling inhibitor exhibited less lethal potency in intracranial transplantation assay. These results identify an essential pathway for GICs, the TGF-beta-Sox4-Sox2 pathway, whose disruption would be a therapeutic strategy against gliomas.

Bone. 2009 Nov 4;
Wiren KM, Semirale AA, Hashimoto JG, Zhang XW

Periosteal expansion is a recognized response to androgen exposure during bone development and in profoundly hypogonadal adults. However, androgen also suppresses endocortical bone formation, indicating that its effects on bone are dichotomous and envelope-specific. In fact, enhanced androgen signaling has been shown to have dramatic detrimental effects on whole bone biomechanical properties in two different transgenic models with skeletally targeted androgen receptor (AR) overexpression. As the mechanisms underlying this response are uncharacterized, we compared patterns of gene expression in periosteum-free cortical bone samples derived from AR-overexpressing transgenic male mice and their wild-type counterparts. We then assessed direct androgen effects in both wild-type and AR-overexpressing osteoblasts in primary culture. Among major signaling pathways associated with bone formation, focused quantitative RT-PCR (qPCR) array-based analysis of endocortical bone gene expression from wild-type vs. transgenic males identified the transforming growth factor-beta (TGF-beta) superfamily and bone morphogenetic protein (BMP) signaling as significantly altered by androgen in vivo. Bioinformatic analyses indicated proliferation, osteoblast differentiation and mineralization as major biological processes affected. Consistent with the in vivo array data and bioinformatic analyses, inhibition of differentiation observed with androgen exposure was reduced by exogenous BMP2 treatment of AR-overexpressing cultures to stimulate BMP signaling, confirming array pathway analysis. In addition, nonaromatizable dihydrotestosterone (DHT) inhibited osteoblast proliferation, differentiation and several indices of mineralization, including mineral accumulation and mineralized nodule formation in primary cultures from both wild-type and AR-transgenic mice. These findings identify a molecular mechanism based on altered BMP signaling that contributes to androgen inhibition of osteoblast differentiation and mineralization. Such detrimental effects of androgen on osteoblast function may underlie the generally disappointing results of androgen therapy.

Cytokine Growth Factor Rev. 2009 Nov 3;
Hata A, Davis BN

microRNAs (miRNAs) are small, non-coding RNAs that modulate diverse biological functions through the repression of target genes. miRNA profiling studies have indicated that the levels of miRNAs are altered during normal development and pathogenesis of various diseases, including cancer and cardiovascular disorders. The signaling pathways which control miRNA biogenesis and the mechanisms of regulation, however, are not well understood. Following transcription, mature miRNAs are generated through a series of coordinated processing events mediated by large protein complexes. We recently found that signal transducers of the Transforming Growth Factor beta (TGFbeta) signaling pathway, the Smads, play a regulatory role in the processing of miRNA in the nucleus. In this review, we summarize the current understanding of the regulation of miRNA biogenesis mediated by the TGFbeta signaling pathway.

Cytokine Growth Factor Rev. 2009 Nov 3;
Seuntjens E, Umans L, Zwijsen A, Sampaolesi M, Verfaillie CM, Huylebroeck D

Ligands of the Transforming Growth Factor type beta (TGFbeta) family exert multiple and sometimes opposite effects on most cell types in vivo depending on cellular context, which mainly includes the stage of the target cell, the local environment of this cell or niche, and the identity and the dosage of the ligand. Significant progress has been made in the molecular dissection of the regulation of the activity of the ligands and their intracellular signal transduction pathways, including via the canonical Smad pathway where Smads interact with many transcription factors. This knowledge together with results from functional studies within the embryology and stem cell research fields is giving us insight in the role of individual ligands and other components of this signaling system and where and how it regulates many properties of embryonic and adult stem/progenitor cells, which is anticipated to contribute to successful cell-based therapy in the future. We review and discuss recent progress on the effects of Nodal/Activin and Bone Morphogenetic Proteins (BMPs) and their canonical signaling in cells with stem cell properties. We focus on embryonic stem cells and their maintenance and pluripotency, and conversion into selected cell types of neuroectoderm, mesoderm and endoderm, on induced pluripotent cells and on neurogenic cells in the adult brain.