Induction of DNA synthesis by cholera toxin in the temperature-sensitive cell-cycle mutants of rat 3Y1 fibroblasts at a restrictive temperature

Four temperature-sensitive mutants of rat 3Y1 fibroblasts representing separate complementation groups (3Y1tsD123, 3Y1tsF121, 3Y1tsG125 and 3Y1tsH203) are arrested at a restrictive temperature of 39.8 degrees C mainly with a G1-phase DNA content (temperature arrest). Cholera toxin (CT) (3 micrograms ml-1) induced DNA synthesis at 39.8 degrees C in the temperature-arrested cultures of two mutants (3Y1tsD123 and 3Y1tsG125). This effect of CT was not mimicked by other agents known to elevate the cellular level of cyclic AMP, such as dibutyryl-cyclic AMP, prostaglandin E1 and forskolin, suggesting that the elevation of cellular cyclic AMP level per se is not responsible for the induction of DNA synthesis by CT. Addition of the B subunit of CT to the temperature-arrested cultures of 3Y1tsD123 and 3Y1tsG125 did not induce DNA synthesis at 39.8 degrees C, indicating that the binding of CT to the cell surface alone is insufficient for the induction. The CT-treated cell membrane fraction prepared from temperature-arrested 3Y1tsG125 cells had similar activity for [32P]ADP-ribosylation of the 45 X 10(3) Mr protein to that prepared from cells proliferating at a permissive temperature of 33.8 degrees C. All these results suggest that 3Y1tsG125 cells utilize a CT-responsive signal transduction pathway, different from adenylate cyclase cascade, for preparation for entry into S phase in the temperature-arrested 3Y1tsG125.(ABSTRACT TRUNCATED AT 250 WORDS)