Inhibin is an atypical member of the TGFbeta family of signaling ligands and is classically understood to function via competitive antagonism of activin ligand binding. Inhibin-null (Inha-/-) mice develop both gonadal and adrenocortical tumors, the latter of which depend upon gonadectomy for initiation. We have previously shown that gonadectomy initiates adrenal tumorigenesis in Inha-/- mice by elevating production of LH, which drives aberrant proliferation and differentiation of subcapsular adrenocortical progenitor cells. In this study, we demonstrate that LH signaling specifically up-regulates expression of TGFbeta2 in the subcapsular region of the adrenal cortex, which coincides with regions of aberrant Smad3 activation in Inha-/- adrenal glands. Consistent with a functional interaction between inhibin and TGFbeta2, we further demonstrate that recombinant inhibin-A antagonizes signaling by TGFbeta2 in cultured adrenocortical cells. The mechanism of this antagonism depends upon the mutual affinity of inhibin-A and TGFbeta2 for the signaling coreceptor betaglycan. Although inhibin-A cannot physically displace TGFbeta2 from its binding sites on betaglycan, binding of inhibin-A to the cell surface causes endocytic internalization of betaglycan, thereby reducing the number of available binding sites for TGFbeta2 on the cell surface. The mechanism by which inhibin-A induces betaglycan internalization is clathrin independent, making it distinct from the mechanism by which TGFbeta ligands themselves induce betaglycan internalization. These data indicate that inhibin can specifically antagonize TGFbeta2 signaling in cellular contexts where surface expression of betaglycan is limiting and provide a novel mechanism for activin-independent phenotypes in Inha-/- mice.
"In addition, TβRIII binds inhibins with high affinity, potentiating the exclusion of ACTRIB (ALK4) to antagonize activin-mediated functions , –. Also, TβRIII enables inhibins to antagonize BMP signaling  and to reduce TGF-β2 signals through the endocytic internalization of TβRIII . Conversely, TβRIII also allow TGF-β1 and 2 to attenuate inhibin-mediated functions by downregulating the expression and binding of this co-receptor , . "
[Show abstract][Hide abstract] ABSTRACT: TGF-β type III receptor (TβRIII) is a coreceptor for TGFβ family members required for high-affinity binding of these ligands to their receptors, potentiating their cellular functions. TGF-β -, bone morphogenetic proteins (BMP2/4) and inhibins regulate different checkpoints during T cell differentiation. Although TβRIII is expressed on hematopoietic cells, the role of this receptor in the immune system remains elusive. Here, we provide the first evidence that TβRIII is developmentally expressed during T cell ontogeny, and plays a crucial role in thymocyte differentiation. Blocking of endogenous TβRIII in fetal thymic organ cultures led to a delay in DN-DP transition. In addition, in vitro development of TβRIII(-/-) thymic lobes also showed a significant reduction in absolute thymocyte numbers, which correlated with increased thymocyte apoptosis, resembling the phenotype reported in Inhibin α (-/-) thymic lobes. These data suggest that Inhibins and TβRIII may function as a molecular pair regulating T cell development.
PLoS ONE 08/2012; 7(8):e44217. DOI:10.1371/journal.pone.0044217 · 3.23 Impact Factor
"This function of betaglycan was independent of TGF␤ stimulation, which suggests that inhibins may act via betaglycan instead to regulate motility in ovarian epithelial cells. This pathway may play a similar role in other inhibin target tissues such as adrenal (Looyenga et al., 2010) and endometrium (Florio et al., 2005), although generally betaglycan's role in mediating inhibin action in these tissues is not well-defined. Betaglycan also appears to act as a tumor suppressor in many other tissues, as well, broadly inhibiting the development of metastatic features; most often, this role has been linked to betaglycan's role as a TGF␤ accessory receptor (extensively reviewed elsewhere, see Gatza et al., 2010; Stenvers and Findlay, 2010). "
[Show abstract][Hide abstract] ABSTRACT: Betaglycan is a co-receptor for the TGFβ superfamily, particularly important in establishing the potency of its ligands on their target cells. In recent years, new insights have been gained into the structure and function of betaglycan, expanding its role from that of a simple co-receptor to include additional ligand-dependent and ligand-independent roles. This review focuses on recent advances in the betaglycan field, with a particular emphasis on its newly discovered actions in mediating the trafficking of TGFβ superfamily receptors and as a determinant of the functional output of TGFβ superfamily signalling. In addition, this review encompasses a discussion of the emerging roles of the betaglycan/inhibin pathway in reproductive cancers and disease.
"On the other hand follistatin expression was also significantly decreased (Hofland et al., 2006), which confirms the tight interrelation between follistatin and activin. Finally , expression levels of TGF-b2, implicated in gonadectomy-induced adrenocortical tumor formation in the Inha À/À mice (Looyenga et al., 2010), and its receptor TGF-bR1 were increased in carcinomas compared to adenomas in the micro-array study (de Fraipont et al., 2005). Mutations in several other TGF-b superfamily receptors and Smad proteins are also frequent findings in human cancer tissues (Elliott and Blobe, 2005; Massague, 2008). "
[Show abstract][Hide abstract] ABSTRACT: The adrenal gland is composed of two separate endocrine tissues that control a multitude of bodily functions in their adaptation to external and internal stressors through hormone secretion. The functions of the adrenal gland are regulated by circulating, neural and local factors that ensure proper cell growth and hormone production. Activins and inhibins are among the locally expressed growth factors affecting adrenal cell function. They have been found to influence several aspects of adrenal cell development, adrenocortical steroidogenesis, adrenocortical tumor formation and adrenomedullary cell differentiation. Especially the finding that inhibin α-subunit knockout mice develop adrenocortical carcinomas after gonadectomy has prompted research on the physiological and pathophysiological roles of activin and inhibin in the adrenal cortex. It is now clear that both peptides control adrenocortical physiology and are involved in adrenocortical tumorigenesis at multiple levels, both in murine models as well as in human patients.
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