Intracellular dynamics of Smad‐mediated TGFβ signaling

Abstract

The transforming growth factor-beta (TGFbeta) family represents a class of signaling molecules that plays a central role in morphogenesis, growth, and cell differentiation during normal embryonic development. Members of this growth factor family are particularly vital to development of the mammalian secondary palate where they regulate palate mesenchymal cell proliferation and extracellular matrix synthesis. Such regulation is particularly critical since perturbation of either cellular process results in a cleft of the palate. While the cellular and phenotypic effects of TGFbeta on embryonic craniofacial tissue have been extensively catalogued, the specific genes that function as downstream mediators of TGFbeta action in the embryo during palatal ontogenesis are poorly defined. Embryonic palatal tissue in vivo and murine embryonic palate mesenchymal (MEPM) cells in vitro secrete and respond to TGFbeta. In the current study, elements of the Smad component of the TGFbeta intracellular signaling system were identified and characterized in cells of the embryonic palate and functional activation of the Smad pathway by TGFbeta1, TGFbeta2, and TGFbeta3 was demonstrated. TGFbeta-initiated Smad signaling in cells of the embryonic palate was found to result in: (1) phosphorylation of Smad 2; (2) nuclear translocation of the Smads 2, 3, and 4 protein complex; (3) binding of Smads 3 and 4 to a consensus Smad binding element (SBE) oligonucleotide; (4) transactivation of transfected reporter constructs, containing TGFbeta-inducible Smad response elements; and (4) increased expression of gelatinases A and B (endogenous genes containing Smad response elements) whose expression is critical to matrix remodeling during palatal ontogenesis. Collectively, these data point to the presence of a functional Smad-mediated TGFbeta signaling system in cells of the developing murine palate.

The Amyloid-β Peptide Suppresses Transforming Growth Factor-β1-induced Matrix Metalloproteinase-2 Production via Smad7 Expression in Human Monocytic THP-1 Cells

“…Results from the present study clearly demonstrate that transcription of the MMP-2 gene containing the three putative SBEs can be functionally activated by all three TGF-␤ isoforms, thus confirming both the functionality of the Smad-mediated TGF-␤ signaling pathway and the presence of the three TGF-␤ receptors in human monocytic THP-1 cells. This Smad-mediated MMP-2 production, in response to TGF-␤1, is in good agreement with recent studies (47). However, the minimal effect on monocytic MMP-9 activity exhibited by TGF-␤s in this study is not in good agreement with published reports (47)(48)(49)(50) in which contrasting results are reported.…”

“…This Smad-mediated MMP-2 production, in response to TGF-␤1, is in good agreement with recent studies (47). However, the minimal effect on monocytic MMP-9 activity exhibited by TGF-␤s in this study is not in good agreement with published reports (47)(48)(49)(50) in which contrasting results are reported. Treatment with TGF-␤s has been demonstrated to result in either down-regulation or up-regulation of MMP-9 production, possibly due to differences in cell types and/or experimental conditions.…”

“…Furthermore, A␤1-42 consistently suppressed the TGF-␤1-mediated activation of p3TP-Lux, a well characterized TGF-␤-responsive construct, which contains SBEs capable of conferring TGF-␤ responsiveness on a luciferase reporter. This construct has been used extensively to characterize transcriptional responsiveness to both TGF-␤1 and Smads in a variety of primary cells in culture and established cell lines (17,34,47). We observed that Smad7 depletion by the siRNA method significantly ameliorated or reversed the A␤1-42-mediated suppression of both TGF-␤1-inducible luciferase reporter activity and TGF-␤1-mediated MMP-2 induction.…”

Transforming growth factor β1 is not a reliable biomarker for valvular fibrosis but could be a potential serum marker for invasiveness of prolactinomas (pilot study)

“…Drug-induced activation of 5HT 2b receptors in cardiac valves leads to the dissociation of the heterotrimeric G-protein, the Gaq subunit of which activates phospholipase C, protein kinase C cascade, steroid receptor coactivator, and ERKs, resulting in the upregulation of the expression of TGFb1 (39,40). TGFb1 increases the production of collagen by a dual mechanism: activation of the collagen type I gene promoter via second messengers (SMAD proteins) and stimulation of the translation of other profibrotic factors such as connective tissue growth factor and MMPs, especially MMP2, which facilitates the motility and migration of cardiac fibroblasts (41,42,43). A strong negative correlation has been found between the increased local expression of TGFb1 and its serum levels, which have been shown to be significantly lower in subjects with advanced coronary atherosclerosis and degenerative mitral and aortic regurgitation in comparison with healthy controls (44,45,46).…”

Genetic Aspects of Cleft Lip and Palate ? A Review

“…Furthermore role of TGF-β is very interesting in the formation of the palate, especially during elevation of palatal shelves and fusion. TGF-β 1 and 2 seem to accelerate this function whereas TGF-β 3 is found to have inhibitory roles and these growth factors seem to be controlled by the Smad signaling network [18].…”