Proglucagon gene expression and posttranslational processing in a hamster islet cell line.
Expression of the gene encoding glucagon was studied using a BK virus-induced glucagon-producing hamster islet cell line, InR1-G9 cells. Southern blot analysis of InR1-G9 DNA demonstrated that glucagon gene sequences are not amplified, yet appear to be hypomethylated compared to hamster liver or kidney DNA. Northern blot analysis of RNA from InR1-G9 cells detected a single glucagon mRNA species of 1300 basepairs. Phorbol esters and sodium butyrate, agents that increase glucagon gene transcription in RIN1056A cells, have no effect on glucagon mRNA levels in InR1-G9 cells. Posttranslational processing of proglucagon, as analyzed by gel filtration chromatography and RIA, resulted in the liberation of glucagon, glucagon-like peptide I, and glucagon-like peptide II, partially mimicking the processing of proglucagon in pancreas and intestine, yet differing from that previously observed in RIN1056A cells. Secretion of glucagon and the glucagon-like peptides was stimulated 3-fold after 1-h incubations with phorbol esters. These observations suggest that the determinants of glucagon gene expression and the posttranslational processing of proglucagon are highly cell specific and provide a new model for the study of proglucagon biosynthesis.
Department of Medicine, Toronto General Hospital, University of Toronto, Ontario, Canada.
D J
DJ
Drucker
J
J
Philippe
S
S
Mojsov
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D005796:Genes; D005934:Glucagon / Q000235:genetics*; D007340:Insulinoma; D008745:Methylation; D010190:Pancreatic Neoplasms; D052336:Proglucagon; D011498:Protein Precursors / Q000235:genetics*; D011499:Protein Processing, Post-Translational; D012334:RNA, Neoplasm / Q000235:genetics; D014158:Transcription, Genetic
D011498:Protein Precursors; D012334:RNA, Neoplasm; D052336:Proglucagon; D005934:Glucagon