Possible regulation of macromolecular biosynthesis in mammalian cells by a novel dinucleoside polyphosphate (HS3) produced during step-down growth conditions.

Abstract

AbstractShortly after the withdrawal of L‐glutamine from the growth medium of Chinese hamster ovary (CHO) cells, the rate of synthesis of a bizarre dinucleoside polyphosphate, HS3, increased by 5‐ to 6‐fold. This elevated rate of synthesis was maintained for six hours before it gradually declined to basal level 22 hours later. The pool size of HS3 increased and decreased coincidentally with rate changes. Withdrawal of L‐isoleucine did not affect HS3 biosynthesis. A glycine, adenosine, thymidine (GAT−) auxotroph of CHO cells accumulated HS3 when adenosine, not glutamine, was withdrawn. Replenishment of either glutamine (“wild type” cells) or adenosine (GAT− cells) caused an immediate depletion of HS3 intracellularly.When HS3 accumulated in CHO cells, DNA and RNA synthesis decreased and, vice versa. A similar correlation was not seen for protein synthesis. But, inhibition of protein synthesis by either puromycin or cycloheximide, and of RNA biosynthesis by actinomycin D facilitated HS3 depletion in L‐glutamine starved cells.Mutant CHO cells that are deficient in purine salvage metabolism, HGPRT− (hypoxanthine‐guanine phosphoribosyltransferase) failed to deplete their accumulated HS3 when fed with hypoxanthine, whereas the “wild type” CHO cells responded accordingly. The available data suggest that HS3 metabolism is connected with de novo and salvage pathways of nucleotide biosynthesis, and may play a crucial role in regulating nucleic acid metabolism in CHO cells under conditions of nutritional stress.