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Insulin‐like growth factor I regulation of transcription and replicating enzyme induction necessary for DNA synthesis
Author(s) -
Yang Henry C.,
Pardee Arthur B.
Publication year - 1986
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041270309
Subject(s) - thymidylate synthase , cycloheximide , dna synthesis , biology , microbiology and biotechnology , thymidine kinase , transcription (linguistics) , transcription factor , biochemistry , dna , protein biosynthesis , genetics , gene , fluorouracil , virus , linguistics , philosophy , chemotherapy , herpes simplex virus
Insulin‐like growth factor I (IGF‐I) regulation of the sequence of transcriptional, translational, and postranslational events during G 1 that are necessary for DNA synthesis, and the induction of thymidine kinase and in vivo thymidylate synthase activities was studied in synchronized confluent BALB/c 3T3 mouse fibroblasts. IGF‐I was the only growth factor necessary from 6 to 2½ hours before S phase for onset of DNA synthesis. 5,6 dichlororibofuranosylbenzimidazole (DRB), an inhibitor of transcription, was ineffective in blocking DNA synthesis and increase of both enzyme activities during an interval of about 2½ hours before S phase. Cycloheximide, an inhibitor of translation, was ineffective in blocking DNA synthesis and the increase of in vivo thymidylate synthase activity during an interval of about 1½ hours before S phase but was effective in blocking the increase of thymidine kinase activity up to the G 1 /S boundary. The results demonstrate that IGF‐I is dispensable beyond the R‐point (2–3 hours before S phase), the time when serum factors are no longer necessary for the initiation of DNA synthesis, and that IGF‐I regulates transcriptional events necessary for both DNA synthesis and the induction of thymidine kinase and in vivo thymidylate synthase. The results also demonstrate a posttranslational interval for in vivo thymidylate synthase, suggesting posttranslational modification of this enzyme.