Induction of c-sis mRNA and activity similar to platelet-derived growth factor by transforming growth factor beta: a proposed model for indirect mitogenesis involving autocrine activity.

Abstract

Treatment of quiescent cultures of mouse embryo-derived AKR-2B cells with transforming growth factor (3 resulted in an early induction of c-sis mRNA. The increase in c-sis mRNA was followed by a corresponding increase in protein similar to platelet-derived growth factor (PDGF) in the culture medium. In addition, PDGF-regulated genes (c-fos and c-myc) were stimulated by transforming growth factor 13 with delayed kinetics relative to that seen in other cell systems with direct PDGF stimulation. A model is proposed in which the monolayer mitogenicity of transforming growth factor 13 is mediated by the induction of c-sis and PDGF and the subsequent autocrine stimulation of c-fos, c-myc, and other PDGFinducible genes.The traverse of G, proceeds by an ordered sequence ofevents under growth factor control (1, 2). The cellular responses subsequent to growth factor binding are of great interest. A strategy, or at least an accepted paradigm, has evolved for regulating growth at the level of protooncogene transcription (3, 4). For instance, platelet-derived growth factor (PDGF), the polypeptide believed to be responsible for initiating cell cycle traverse in many mesenchymal cells (5), stimulates a rapid and transient induction of both c-fos and c-myc mRNA in quiescent cells (6)(7)(8). The product of the c-sis protooncogene is the B chain of PDGF while the c-erbB gene product is homologous to the cytoplasmic domain of the epidermal growth factor (EGF) receptor (9-12). Moreover, it has been shown that the receptor for colony stimulating factor 1, a macrophage growth factor, is similar or identical to the product of the c-fms protooncogene (13 MATERIALS AND METHODSCell Culture. Mouse embryo-derived AKR-2B cells (14-16) were grown in McCoys 5A medium as described (16). To prepare cultures for RNA purification, 300,000 cells/100-mm Petri dish were cultured in serum-supplemented McCoys SA medium and allowed to grow to confluence. On day 5 after plating the spent medium was removed and fresh serum-frfe MCDB 402 (Kansas City Biologicals, Lenexa, KS) was added for an additional 2 days to assure quiescence and removal'of residual serum factors (16). Cultures were then stimulated for the indicated period of time with fresh MCDB 402 alone (containing 10 ,g of Pentex bovine serum albumin/ml) (Miles) or supplemented with the indicated reagents (also containing 10 ,ug of bovine serum albumin/ml). TGF-,8 from human platelets was purified by a modification of the method of Assoian et al. (17) as described by Tucker et al. (18). The platelet TGF-,B was shown to be homogenous by silver staining of NaDodSO4/polyacrylamide gels under reducing and nonreducing conditions and autoradiography of gels of reduced and nonreduced 1251-labeled . RNA Isolation. Cytoplasmic poly(A)+-containing RNA was prepared by a modification of published procedures (19). Subsequent to stimulation cultures were scraped with a rubber policeman and collected by centrifugation (235 x g for 5 min). The cell pellet was resuspended in lysing buffer (140 mM NaCl/1...

Expression and autoregulation of transforming growth factor β receptor mRNA in small-cell lung cancer cell lines

“…Four cell lines expressed betaglycan mRNA despite lack of beta-glycan protein expression (Table I). We could conclude that no deletion or translocation of the beta-glycan gene had occurred in these cell lines, since they all expressed a -7.0 kb transcript (Figure 1) Massague, 1985), platelet-derived growth factor (Leof et al, 1986;Win et al, 1993) and fibroblast growth factor (Kikuchi et al, 1992). In addition, TGF-/31 was shown to increase, i.e.…”

Transforming growth factor beta 1-responsive element: closely associated binding sites for USF and CCAAT-binding transcription factor-nuclear factor I in the type 1 plasminogen activator inhibitor gene.

“…In at least some cases, the growth-inhibitory effect of TGF-, is caused by a decrease in transcription of the c-myc gene (36), which is probably mediated by inhibition of phosphorylation of the retinoblastoma susceptibility gene product, pRB (20,21,31,37). In contrast, the growth-stimulatory effect on some connective tissue cells appears to be mediated by the stimulation of an autocrine mechanism involving plateletderived growth factor secretion (2,25).…”

Mitogen crosstalk accompanying urokinase receptor expression in stimulated vascular smooth muscle cells

“…At sites of fracture of atheromatous plaques, platelets accumulate setting the stage for thrombin generation which can initiate and propagate an intravascular thrombus and also act as a mitogen for adjacent cells in the vessel wall. Thrombin in addition to other growth factors may not work separately in the propagation of atheromatous plaque formation but may act cooperatively with other growth factors through additive, synergistic or 'cascade-like' effects [12].…”