A biochemical investigation of the adenovirus‐induced G1 to S phase progression: Thymidine kinase, ornithine decarboxylase, and inhibitors of polyamine biosynthesis

Abstract

Biochemical events were investigated in the G1 to S phase progression induced in quiescent rodent cells by human adenovirus type 5 (Ad5) and by serum. Thymidine kinase activity increased after infection of cells with Ad5 or addition of 10% serum. These stimulations were additive. An early viral gene was responsible for induction by Ad5, but the early mutants ts36, ts37, and ts125 induced thymidine kinase at the permissive and nonpermissive temperatures. Several differences were found between cells stimulated by serum compared with Ad5. Induction of thymidine kinase was delayed in Ad5-infected cells, insensitive to 0.01 microgram/ml actinomycin D and relatively resistant to reduced Ca2+ compared with induction by serum. Ornithine decarboxylase was induced by serum, but not by Ad5, alpha-Methylornithine had little effect on the induction of thymidine kinase by Ad5, but reduced the induction of thymidine kinase by serum, suggesting that Ad5-induced entry into S phase is uncoupled from polyamine biosynthesis. Methylglyoxal bis(guanylhydrazone), however, prevented the induction of thymidine kinase by both serum and Ad5. Adenovirus infection appears to induce cellular DNA synthesis and thymidine kinase in G1-arrested cells by a mechanism different from serum, and bypasses events in the normal G1 to S phase progression.

Adenovirus type 2 activates cell cycle-dependent genes that are a subset of those activated by serum.

“…Histone gene expression has only been studied in permissive cells (24). ODC activity was found not to increase in Ad2-infected cells (15,16). Our data show that the RNA levels do increase.…”

“…First of all, it bypasses the temperature-sensitive block in G1 (63), a property it shares with simian virus 40 (25), whereas serum or retroviral oncogenes completely fail to do so (3,25,33,63). Second, the stimulation of cellular DNA synthesis is not accompanied by the increase (actually the doubling) in cellular RNA that regularly accompanies serum stimulation (58; present paper) or ODC activity (15,16). Third, the adenovirusinfected cells synthesize an irregular amount of DNA and do not divide (10,11).…”

“…TK activity has been reported to be increased in some cells after adenovirus infection (15,40), but this is the first time that an increase in TK RNA levels is reported. Other viruses, of course, are known to increase TK activity in cultured cells, for instance, simian virus 40 (36,58), polyomavirus (7), and cytomegalovirus (23).…”

“…ODC activity is also increased after a variety of mitogenic stimulations (15,26,30,67), although there are exceptions (53,55 (21), and this could be another instance. c-ras and 2A9 have also been shown to be expressed in a cell cycle-dependent manner (13,27,28,31) in rat liver and cells in culture.…”

“…At any rate, the effect of adenovirus infection on gene expression in permissive cells has been already discussed in several papers (15,16,23,36,40). The rest of the discussion is therefore limited (unless otherwise noted) to what happens in nonpermissive or semipermissive cells.…”