RNA and protein synthesis and kinetics of processing and release of insulin in cultures of mouse pancreatic beta cells.
Monolayer cultures of mouse pancreatic beta cells were used to study protein composition, the extent and nature of RNA and protein synthesis, and the kinetics of insulin precursors synthesis, precursor processing, and the release of nascent insulin. The cells synthesized both RNA and proteins actively, but the amounts synthesized declined with the age of the culture. The size and spectrum of proteins synthesized in cells soon after isolation and after maintenance in culture were very similar. At least 15 proteins (mol. wt. 66,000 to less than 14,000) were synthesized, including insulin precursors and insulin. Radioactive labeling and chase experiments revealed the synthesis of insulin precursors and insulin continuously. Radioactivity present in the precursors decreased rapidly during the early times of chase. This reduction in radioactivity was partly due to the processing of insulin precursors into insulin and partly due to the release of proinsulin into the medium along with newly synthesized insulin. The residual labeled precursors turned over at a slower rate. It appears that the processing of insulin precursors is two-phase-initially rapid and then slow and prolonged, which could have resulted from two populations of precursors with different half-lives.
D000818:Animals; D002478:Cells, Cultured; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051379:Mice; D011384:Proinsulin / Q000378:metabolism; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis*
D007328:Insulin; D011498:Protein Precursors; D012313:RNA; D011384:Proinsulin