The active principle of a cytosol extract from weanling rat liver representing a putative liver-specific
growth factor was partially purified and characterized. "
Hepatic stimulator substance" was extracted from the livers of 40- to 60-gm male rats by heat treatment of a homogenate in 35% (w/v)
phosphate-buffered saline and subsequent ultracentrifugation. This "heat supernatant" and fractions derived from the subsequent purification steps were tested for growth stimulatory activity in two rat
hepatoma cell lines. The undifferentiated, fibroblastoid-like HTC
hepatoma cells did not respond to crude
hepatic stimulator substance or any of the partially purified preparations. In contrast, MH1C1 cells, which display some differentiated hepatic functions and epithelial morphology, reacted to
hepatic stimulator substance and the purified fractions with a dose-dependent increase of their growth rate in serum-free culture. Although
insulin,
glucagon and
epidermal growth factor showed only a minor effect on MH1C1 cell growth on their own, they were active as permissive or potentiating factors for the expression of the maximal effect of
hepatic stimulator substance. Similarly, normal adult rat hepatocytes were only sensitive to
hepatic stimulator substance when cultured in the simultaneous presence of
epidermal growth factor. Under such conditions,
hepatic stimulator substance stimulated hepatocyte entry into the S-phase of the cell cycle 3-fold compared to
epidermal growth factor alone.
Hepatic stimulator substance did not affect growth of human skin fibroblasts and of the rat intestinal crypt cell line IEC-6.(ABSTRACT TRUNCATED AT 250 WORDS)