SPONTANEOUSLY TRANSFORMED RAT-LIVER EPITHELIAL-CELL LINE PRODUCING AUTOCRINE AND PARACRINE GROWTH-FACTORS

A spontaneously transformed rat-liver epithelial-cell line that could proliferate in unsupplemented, serum-free medium and be passaged with trypsinization has been established. At the time of writing, the line has undergone more than 100 passages in serum-free culture. This cell line produced an autocrine growth-stimulatory factor (AGSF) and a paracrine growth-stimulatory factor (PGSF). AGSF had a remarkable growth-stimulatory effect on transformed rat-liver epithelial-cells, but had no such effect on non-transformed rat-liver epithelial-cells that could not proliferate in serum-free medium. AGSF did not show a growth-inhibitory or stimulatory effect on normal rat kidney (NRK) cells in monolayer culture, and did not induce anchorage-independent growth in soft-agar culture even with epidermal growth factor (EGF) or transforming growth factor (TGF)-beta. AGSF was protease-sensitive, but heat- and acid-stable. The molecular weight was about 700 Dalton (Da) on size-exclusion chromatography. PGSF showed a growth-stimulatory effect on NRK cells and induced anchorage-independent growth in soft-agar culture without EGF or TGF-beta. On the other hand, PGSF slightly inhibited the growth of the spontaneously transformed rat-liver epithelial cells. PGSF was heat-, protease- and acid-sensitive. The molecular weight was 30 kDa on size-exclusion chromatography.