DIFFERENTIATING AND PROLIFERATIVE EFFECTS OF HGF IN RENAL PROXIMAL TUBULAR CELLS ARE MEDIATED VIA DIFFERENT SIGNALING PATHWAYS

Background. As a renotropic cytokine, hepatocyte growth factor (HGF) p revents acute renal failure and accelerates renal regeneration. HGF in itiates its biological effects by interaction with specific transmembr ane receptors, the c-Met proto-oncogene, possessing an intracellular t yrosine kinase domain. We tested the hypothesis of whether the complex biological effects of HGF in renal proximal tubular cells are mediate d by different intracellular signalling cascades and/or different rece ptors. Methods. PT-1 cells, a proximal tubular cell line derived from rabbit kidney, were cultured under defined serum-free conditions to ex amine the biological effects of exogenously added HGF. By specific ass ays, we determined HGF binding and its effects on cell proliferation, migration, scattering and tubulogenic differentiation. To investigate whether HGF action could be inhibited by protein tyrosine kinase inhib itors (PTKIs), cells were incubated with HGF and different concentrati ons of herbimycin A, genestein, methyl-2,5-dihydroxycinnamate (MDC) an d geldanamycin. All PTKIs are known inhibitors of pp60(C-STC), a non-r eceptor tyrosine kinase involved in cell growth control. Results. HGF bound with high affinity to cell membrane receptors and displayed mult iple biological effects. Compared with serum-free controls, HGF increa sed the number of microvilli 1.5-fold, enhanced cell proliferation and migration 1.8-fold, and stimulated the formation of tubular structure s 2.3-fold. Consistent with the known tyrosine kinase activity of the c-Met receptor, the mitogenic and motogenic effects of HGF were inhibi ted by PTKIs in a dose-dependent manner with the following order of po tency: geldanamycin >herbimycin A>genestein > MDC. In contrast, howeve r, the HGF-induced tubulogenic cell differentiation was not inhibited specifically by PTKIs. Conclusions. The finding that PTKIs inhibited t he mitogenic response but not the tubulogenic differentiation induced by HGF indicates different intracellular signal transduction pathways. We suggest that pp60(C-STC) plays a key role in mediating the mitogen ic and motogenic action of HGF, whereas tubulogenic cell differentiati on induced by HGF is transduced by a pp60(C-STC)-independent signallin g pathway.