AJP - Endocrinology and Metabolism, Vol 263, Issue 6 E1106-E1112, Copyright © 1992 by American Physiological Society
Effects of insulin on total RNA, poly(A)+ RNA, and mRNA in primary cultures of rat hepatocytes
C. J. Hsu, S. R. Kimball, D. A. Antonetti and L. S. Jefferson
Department of Cellular and Molecular Physiology, College of Medicine, Pennsylvania State University, Hershey 17033.
The purpose of this study was to examine mechanisms involved in the
regulation of protein synthesis in primary cultures of rat hepatocytes.
Hepatocytes were maintained in a chemically defined serum-free medium in
the presence or absence of insulin. The rate of protein synthesis in
hepatocytes deprived of insulin between days 2 and 5 of culture was reduced
to 67% of the rate observed in insulin-maintained controls. The decrease in
protein synthetic rate was accompanied by a proportional fall in the
content of both total RNA and poly(A)+RNA, suggesting that the capacity for
protein synthesis was reduced in the absence of insulin. Both total RNA and
poly(A)+ RNA contents and the protein synthetic rate were returned to
control values after 3 days of insulin resupplementation. In addition, the
effect of insulin on the expression of specific mRNAs was assessed by in
vitro translation of total RNA followed by two-dimensional gel analysis of
radiolabeled translation products. Only 13 of the greater than 150 spots
discernible on the two-dimensional gels were altered in response to
insulin. The mRNAs that were altered include examples of repression and
stimulation of expression in response to insulin deprivation. Thus, in
isolated rat hepatocytes, insulin regulates the capacity of both overall
protein synthesis as well as the capacity for the synthesis of specific
proteins.
