Activin A Mediates Growth Inhibition and Cell Cycle Arrest through Smads in Human Breast Cancer Cells

Abstract

The transforming growth factor-B (TGF-B) superfamily of growth factors is responsible for a variety of physiologic actions, including cell cycle regulation. Activin is a member of the TGF-B superfamily that inhibits the proliferation of breast cancer cells. Activin functions by interacting with its type I and type II receptors to induce phosphorylation of intracellular signaling molecules known as Smads. Smads regulate transcription of many genes in a cell-and tissue-specific manner. In this study, the role of activin A in growth regulation of breast cancer cells was investigated. Activin stimulated the Smad-responsive promoter, p3TP, 2-fold over control in T47D breast cancer cells. Activin inhibited cellular proliferation of T47D breast cancer cells after 72 hours, an effect that could be abrogated by incubation with the activin type I receptor inhibitor, SB431542. Activin arrested T47D cells in the G 0 -G 1 cell cycle phase. Smad2 and Smad3 were phosphorylated in response to activin and accumulated in the nucleus of treated T47D cells. Infection of T47D cells with adenoviral Smad3 resulted in cell cycle arrest and activation of p3TP-luciferase, whereas a adenoviral dominant-negative Smad3 blocked activin-mediated cell cycle arrest and gene transcription. Activin maintained expression of p21 and p27 cyclin-dependent kinase inhibitors involved in cell cycle control, enhanced expression of p15, reduced cyclin A expression, and reduced phosphorylation of the retinoblastoma (Rb) protein. Smad3 overexpression recapitulated activininduced p15 expression and repression of cyclin A and Rb phosphorylation. These data indicate that activin A inhibits breast cancer cellular proliferation and activates Smads responsible for initiating cell cycle arrest. (Cancer Res 2005; 65(17): 7968-75)

Expression of SMAD proteins, TGF-beta/activin signaling mediators, in human thyroid tissues

“…As illustrated in figure 2, SMAD4 and pSMAD2/3 as well as inhibitory SMAD7 are expressed in all of tumoral stages of thyroid from benign to malignant lesions, whereas these proteins are rarely detected in normal thyroid tissue. SMAD proteins mediate antiproliferative effects by inducing the expression of the CDK inhibitors, p15 and p21, and by inhibiting c-MYC expression in several epithelial cell lines responsive to TGF-β or activin (22,(28)(29)(30). The loss of TGF-β/activin responsiveness caused by inactivation of the signaling pathway's components, such as deletions or mutations in either TGF-β or activin receptors and SMADs, has been identified in the development and progression of a variety of cancers, conferring a potential tumor suppressive role for the SMADs pathway (2,31,32).…”

Activin Type 2 Receptor Restoration in MSI-H Colon Cancer Suppresses Growth and Enhances Migration With Activin

“…Activin signaling induces growth inhibition in T47D human breast cancer cells 3,7 and LNCaP prostate cancer cells 4 and induces apoptosis in hematopoietic and myeloid leukemia cells. 8,9 Cell adhesion proteins are up-regulated through activin signaling in chicken limb buds, suggesting a role in cell anchoring.…”

Activin and estrogen crosstalk regulates transcription in human breast cancer cells

“…Overexpression of ERa in the absence of exogenous estrogen significantly reduced p3TP induction to 50% when compared with cells not overexpressing the receptor. The reduction in baseline expression was predicted based on the high levels of activin A secreted by T47D cells that could be repressed by overexpression of ERa (Burdette et al 2005). The addition of estradiol in combination with overexpressed ERa also significantly inhibited p3TP-induced activation when compared with estrogen treatment alone.…”

“…Only Smad3 was transiently transfected into T47D cells to study its role in estrogen-induced repression of the p3TP promoter due to the fact that p3TP is more responsive to Smad3 expression when compared with Smad2 (Dennler et al 1998). Smad3 transfection results in a ligand-independent activation of the promoter resulting in a 30% increase when compared with control (Dennler et al 1998, Burdette et al 2005. Estrogen alone had no alteration on this activation, while activin further stimulated luciferase production.…”

“…Unfortunately, activin bA knockout mice do not provide information regarding control of mammary cells because palette malformations result in death before the mammary gland develops (Matzuk et al 1995). Activin A in vitro inhibits cell growth by stimulating the phosphorylation of Smad3 and this causes a redistribution of the cell cycle into G 0 /G 1 arrest (Liu et al 1996, Ying & Zhang 1996, Cocolakis et al 2001, Burdette et al 2005. Activins A and B reduce proliferation of cultured rat acini isolated during different stages of mammary gland morphogenesis and differentiation (Bussmann et al 2004).…”