RGD peptides released from βig-h3, a TGF-β-induced cell-adhesive molecule, mediate apoptosis

Abstract

big-h3 is a transforming growth factor-b (TGF-b)-induced cell-adhesive molecule and has an RGD sequence at its Cterminus. A previous report suggested that big-h3 normally undergoes carboxy-terminal processing that results in the loss of the RGD sequence. RGD peptides appear to play various roles in cell function. Here we show that the RGD peptides released from big-h3 may facilitate TGF-b-induced apoptosis. We found that carboxy-terminal cleavage of big-h3 occurred after its secretion, and that overexpression of the wild-type big-h3 induced apoptosis, unlike the C-terminal deleted but RGDcontaining mutant big-h3, which is resistant to C-terminal processing. The big-h3-induced apoptosis was abolished by either deletion of the RGD sequence or mutation of RGD to RAE. Synthetic peptides of ERGDEL and GRGDSP derived from big-h3 and fibronectin, respectively, also induced apoptosis, unlike ERGEEL and GRGESP. Culture supernatants of cells overexpressing big-h3 filtered to isolate molecules smaller than 3 kDa also induced apoptosis. A fusion protein composed of the N-terminal 100 amino acids of fibronectin and the RGDcontaining C-terminal part of big-h3 was also subjected to C-terminal cleavage and overexpression resulted in apoptosis. The anti-big-h3 antibody blocks TGF-binduced apoptosis. Thus, big-h3 may be important in regulating cell apoptosis by providing soluble RGD peptides.

Detection of Differentially Expressed Basal Cell Proteins by Mass Spectrometry

“…The full list of the proteins detected from CAL33 and UM-SCC-1 deroofed cells is provided in supplemental Tables S3 and S4, respectively. Western blots of selected proteins that are known to be involved in tumor progression through their roles in regulating cell-cell adhesion (desmoglein 2 and PG) (41,42), cell-matrix interactions (␤ 4 integrin and ␤Ig-h3) (43)(44)(45), motility and invasion (Rac1) (46), and cell growth and death regulation (␤Ig-h3) (47,48) revealed differential expression and corroborated the mass spectrometry findings (Fig. 4B).…”

TGF-βi Promotes Islet β-Cell Function and Regeneration

“…These biological effects of TGF-bi could be explained by triggering of the cell surface integrin signaling pathways. In contrast, a soluble TGF-bi fragment containing its C-terminal RGD domain induces Chinese hamster ovary cell apoptosis (25). In this case, it is likely that the soluble fragment interferes with normal cell-cell interactions between integrins and fibronectin, as the RGD domain could bind to integrins and dampen their association with fibronectins.…”

“…Its RGD domain at the C terminus binds to integrins. Although the types of its interacting integrins have not been pinpointed (25,26), in theory, the RGD domain should be able to interact with a5b1, a8b1, aVb3, aVb5, aVb6, aVb8, and aIIb3 (27). TGF-bi is also known to bind to a1b1, a6b4, a7b1 (28)(29)(30), but domain(s) involved in such associations have not been re-ported.…”

Two novel VHL targets, TGFBI (BIGH3) and its transactivator KLF10, are up-regulated in renal clear cell carcinoma and other tumors

“…Since TGFBI was previously associated with apoptosis [18,39] and apoptosis is linked with cell survival in general and with hypoxia in particular, we asked if TGFBI expression can be induced by stress-related stimuli. To this end, we studied TGFBI expression in 26 cancer cell lines exposed to 26 chemotherapeutic agents (Suppl.…”

“…TGFBI was also reported to stimulate adhesion, spreading, migration and proliferation in renal proximal tubular epithelial cells [17]. The RGD peptide of TGFBI can be released from the protein and induce apoptosis [18]. Although TGFBI was associated with cancers in various studies [19][20][21][22][23][24][25][26], the molecular mechanisms of its transcriptional regulation remained unknown.…”