Insulin is essential for accumulation of casein mRNA in mouse mammary epithelial cells.
In the presence of cortisol and prolactin, insulin at concentrations as low as 1 ng/ml significantly stimulates casein synthesis in mammary explants from midpregnant mice; maximal synthesis occurs at 10 ng/ml. However, in the absence of insulin, no detectable immunoprecipitable casein is produced. Insulin also supports enhanced accumulation of casein mRNA in the presence of cortisol and prolactin; neither epidermal growth factor nor somatomedin C has this effect. These inductive actions of insulin are not secondary to a general maintenance effect on the mammary epithelial cell; insulin, epidermal growth factor, and somatomedin C can support the accumulation of RNA in rough endoplasmic reticulum equally well. In addition, these effects do not reflect a specific insulin requirement for prolactin sensitivity; epidermal growth factor can support prolactin-induced total RNA synthesis as well as insulin can. The results demonstrate that, although insulin, epidermal growth factor, and somatomedin C can all function as cell maintenance agents, only insulin, together with cortisol and prolactin, can induce casein mRNA accumulation.
D000818:Animals; D002364:Caseins / Q000096:biosynthesis / Q000235:genetics*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I; D008321:Mammary Glands, Animal / Q000502:physiology*; D051379:Mice; D009924:Organ Culture Techniques; D012333:RNA, Messenger / Q000378:metabolism*; D013002:Somatomedins / Q000494:pharmacology
D002364:Caseins; D007328:Insulin; D012333:RNA, Messenger; D013002:Somatomedins; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I