Growth factor(s) produced during infection with an adenovirus variant stimulates proliferation of nonestablished epithelial cells.

Infection of primary baby rat kidney cells with an adenovirus variant that encodes only the 12S gene of the E1A region, adenovirus type 5 (Ad5) 12S, results in the production of a growth factor that stimulates primary epithelial cells to proliferate. Increased epithelial cell DNA synthesis and proliferation is detectable between 24 and 36 hr after the addition of conditioned medium from Ad5 12S infected cells and not from cells infected with an E1A deletion mutant virus, Ad5 dl312. This mitogenic factor(s) is effective in the absence of serum and can override the inhibitory effect of serum on primary epithelial cells. Furthermore, there is a requirement for the continued presence of the growth factor(s) in the Ad5 12S conditioned medium to maintain epithelial cell proliferation, and the conditioned medium can maintain these cells in a proliferative state for at least 6 wk. The stimulatory activity in Ad5 12S conditioned medium is associated with large molecular weight complexes, from which it can be released by 4 M NaCl. Several characteristics of the growth factor(s) indicate that it is a unique mitogen for epithelial cells.