CONCOMITANT EXPRESSION OF HEPATOCYTE GROWTH-FACTOR SCATTER FACTOR ANDTHE RECEPTOR C-MET IN HUMAN MYELOMA CELL-LINES

Myeloma cell line supernatants were screened for their ability to inhi bit the activity of transforming growth factor-beta (TGF beta) in the mink lung cell (Mv-1-Lu) bioassay. Supernatant from the human myeloma cell line JJN-3 contained potent TGF beta antagonistic activity. This activity was isolated and found to be associated with a 72-78-kDa glyc oprotein. Specific polyclonal and monoclonal antibodies were generated toward the 72-78-kDa protein, and these antibodies precipitated the T GF beta inhibitory activity from JJN-3 supernatant. Upon amino acid se quencing the protein appeared to be identical to hepatocyte growth fac tor (HGF), and some of the generated antibodies directly blocked the a ction of recombinant HGF in various assays. By HGF-specific polymerase chain reaction we demonstrated that HGF mRNA was expressed in five ou t of five tested myeloma cell lines. The level of HGF protein in super natants showed great variation from >500 ng/ml in JJN-3 supernatant to a few ng/ml in the supernatants from other myeloma cell lines. The sa me five cell lines were also screened for expression the HGF receptor c-MET. Four of them expressed the receptor as shown by reverse transcr iptase-polymerase chain reaction and Western blot. The receptor was sh own to be constitutively phosphorylated in the human myeloma cell line JJN-3. This receptor could be dephosphorylated by anti-HGF antibodies , indicating the existence of an autocrine HGF loop in this cell line. We propose that HGF/c-MET may play a role in multiple myeloma.