TRANSFORMING GROWTH-FACTOR-BETA INDUCES ANCHORAGE-INDEPENDENT GROWTH OF NRK FIBROBLASTS VIA A CONNECTIVE-TISSUE GROWTH FACTOR-DEPENDENT SIGNALING PATHWAY

Connective tissue growth factor (CTGF) is a M(r) 38,000 cysteine-rich peptide, the synthesis and secretion of which are selectively induced by transforming growth factor beta (TGF-beta). The relationship of CTG F to TGF-beta action on fibroblastic cells is not well understood, TGF -beta has the unique ability to stimulate the growth of normal fibrobl asts in soft agar, a property of transformed cells, We have investigat ed whether CTGF can substitute for TGF-beta or whether CTGF action is essential for TGF-beta to stimulate anchorage-independent growth (AIG) of NRK fibroblasts. Our studies demonstrate that CTGF cannot induce A IG of NRK fibroblasts. However, CTGF synthesis and action are essentia l for the TGF-beta-induced AIG of NRK fibroblasts. Anti-CTGF antibodie s specifically block TGF-beta-induced AIG but have no effect on platel et-derived growth factor or epidermal growth factor-induced growth in monolayer cultures and do not cross-react with platelet-derived growth factor or TGF-beta, Clones of NRK fibroblasts that express an antisen se CTGF gene (NRK-ASCTGF), which blocks the expression of the endogeno us CTGF gene, do not respond to TGF-beta in the AIG assay, The growth and morphology of the cells (NRK-ASCTGF) in monolayer culture are unal tered from the parent NRK cell line, The addition of recombinant CTGF to the NRK-ASCTGF clones in the presence of TGF-beta restores the AIG response of the cells, These studies demonstrate that the TGF-beta sti mulation of NRK fibroblast AIG is dependent on events induced via the synergistic action of CTGF-dependent and CTGF-independent signaling pa thways.