Insulin Regulation of Nuclear Envelope Functions: Relationship to mRNA Metabolism
Insulin is a major anabolic hormone for most mammalian species. The hormonal potency of insulin results, to a large extent, from its ability to regulate target cells at a variety of cellular sites. The effects of insulin on membrane transport, enzyme activity, and protein synthesis have been studied extensively. Most likely many of these effects result from the direct interaction of insulin with its plasma membrane receptor. Insulin also regulates nuclear functions such as DNA and RNA synthesis, but how insulin influences these processes is unknown. The presence of specific binding sites for insulin on nuclei and nuclear envelopes has been documented and characterized. These binding sites have biochemical characteristics that are different from insulin binding sites on the plasma membrane. Moreover, direct in vitro effects of insulin on messenger RNA (mRNA) metabolism have now been reported. These effects include: (1) stimula- tion of mRNA efflux from intact nuclei; (2) stimulation of nuclear envelope nucleoside triphosphatase (NTPase), the enzyme that regulates mRNA efflux; and (3) inhibition of 32P incorporation into nuclear envelopes. Thus, significant insight is now being gained concerning the actions of insulin on nuclear function.
KeywordsNuclear Envelope Nuclear Membrane Nuclear Pore Complex Insulin Binding Orotic Acid
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