Transforming Growth Factor β1 (TGF-β1) Promotes Endothelial Cell Survival during In Vitro Angiogenesis via an Autocrine Mechanism Implicating TGF-α Signaling

Abstract

Mouse capillary endothelial cells (1G11 cell line) embedded in type I collagen gels undergo in vitro angiogenesis. Cells rapidly reorganize and form capillary-like structures when stimulated with serum. Transforming growth factor ␤1 (TGF-␤1) alone can substitute for serum and induce cell survival and tubular network formation. This TGF-␤1-mediated angiogenic activity depends on phosphatidylinositol 3-kinase (PI3K) and p42/p44 mitogen-activated protein kinase (MAPK) signaling. We showed that specific inhibitors of either pathway (wortmannin, LY-294002, and PD-98059) all suppressed TGF-␤1-induced angiogenesis mainly by compromising cell survival. We established that TGF-␤1 stimulated the expression of TGF-␣ mRNA and protein, the tyrosine phosphorylation of a 170-kDa membrane protein representing the epidermal growth factor (EGF) receptor, and the delayed activation of PI3K/Akt and p42/p44 MAPK. Moreover, we showed that all these TGF-␤1-mediated signaling events, including tubular network formation, were suppressed by incubating TGF-␤1-stimulated endothelial cells with a soluble form of an EGF receptor (ErbB-1) or tyrphostin AG1478, a specific blocker of EGF receptor tyrosine kinase. Finally, addition of TGF-␣ alone poorly stimulated angiogenesis; however, by reducing cell death, it strongly potentiated the action of TGF-␤1. We therefore propose that TGF-␤1 promotes angiogenesis at least in part via the autocrine secretion of TGF-␣, a cell survival growth factor, activating PI3K/Akt and p42/p44 MAPK.

Cyclooxygenase-2 overexpression abrogates the antiproliferative effects of TGF-β

“…This may be changed dramatically in hyperproliferating cells as in adenomas or less differentiated cells, which may lose polarity (Huang et al, 1995). On the other hand, TGF-b has been shown to induce TGF-a expression with the consequence of EGF-receptor activation (Vinals and Pouyssegur, 2001) and an increase in c-myc oncogene expression (Skouteris and McMenamin, 1992), as we could demonstrate in the transfected cells here (Supplementary Figure 4). Although direct prostaglandin effects via exogenous receptor activation are a good explanation, endogenously produced lipid mediators may also mediate effects.…”

Transforming growth factor β1 induction of vascular endothelial growth factor receptor 1: Mechanism of pericyte-induced vascular survival in vivo

“…In vitro studies implicate a role for TGF-␤ in vascular cell maturation and inhibition of proliferation, perhaps through suppression of VEGFR-2 (25,26). Cocultures of pericytes and endothelial cells activate TGF-␤ (12,14), which inhibits proliferation and causes differentiation of vascular cells (13,15,27,28). However, work in vivo has been more limited, except for genetic alterations in mice.…”

“…In vitro, pericyte͞endothelial cell cocultures are associated with transforming growth factor (TGF)-␤ expression and activation (12)(13)(14), which in turn promote vascular cell differentiation and suppress proliferation (13,15). Thus, we examined whether TGF-␤1 was also involved in vessel survival in vivo.…”

Requirement of BMP-2-induced Phosphatidylinositol 3-Kinase and Akt Serine/Threonine Kinase in Osteoblast Differentiation and Smad-dependent BMP-2 Gene Transcription

“…Recently a role of PI 3-kinase has been shown in TGF-␤-induced epithelial and endothelial cell survival and epithelial to mesenchymal transition (19,44,45) indicating that activation of serine/threonine kinase receptor utilizes this central lipid kinase as one of the signaling mechanisms similar to receptor tyrosine kinases. Recently PI 3-kinase has been implicated in myogenic differentiation (13,46,47).…”