Insulin induces rapid accumulation of insulin receptors and increases tyrosine kinase activity in the nucleus of cultured adipocytes

Abstract

To better understand the mechanism by which insulin exerts effects on events at the cell nucleus, we have studied insulin receptors and tyrosine kinase activity in nuclei isolated by sucrose density gradient centrifugation following insulin treatment of differentiated 3T3-F442A cells. Insulin stimulated nuclear accumulation of insulin receptors by approximately threefold at 5 min. The half-maximal effect was observed with 1-10 nM insulin. Following insulin treatment, phosphotyrosine content associated with the nuclear insulin receptor was also increased by twofold at 5 min with a similar insulin concentration dependency. These nuclear insulin receptors differ from the membrane-associated insulin receptors in that they were not efficiently solubilized with 1% Triton X-100. During the same period of time, insulin stimulated nuclear tyrosine kinase activity toward the exogenous substrate poly Glu4:Tyr1 tenfold in a time-dependent manner reaching a maximum at 30 min. The insulin receptor substrate protein 1 (IRS-1) could not be detected in the nucleus by immunoblotting. However, a nuclear protein with M(r) approximately 220 kDa was tyrosine phosphorylated, and insulin further stimulated this process threefold > 30 mins. Surface labeling was performed to determine if the nuclear insulin receptors would emerge from the plasma membrane fraction. Using 125I-BPA-insulin with intact cells, the intensity of nuclear insulin receptor labeling was negligible and not increased throughout 30 min incubation at 37 degrees C. In contrast, there was an increase in labeled receptors in the microsomal fraction following insulin treatment. Taken together, these results indicate that insulin rapidly increases nuclear insulin receptor appearance and activates nuclear tyrosine kinase activity. The insulin-induced accumulation of nuclear insulin receptors cannot be accounted for by internalization of surface membrane receptors. These effects of insulin may play an important role in action of the hormone at the nuclear level.

Intracellular presence of insulin and its phosphorylated receptor in non‐small cell lung cancer

“…3A) which is in agreement with a previously reported nuclear insulin receptor activity (Kim and Kahn, 1993).…”

Insulin Stimulates Production of Nitric Oxide via ERK in Osteoblast Cells

“…The levels of NO produced by insulin in the UMR-106 cells are in the significantly lower range (approximately 3-6 M) as compared to those found in cytokine-mediated NO generation (over 30 M) (37). Cytokine-induced NO production is known to reduce osteoblast activity (36); however, small increase of NO production by insulin found in the present study had little effect on alkaline phosphatase activity. We think that the relatively small amounts of NO produced by insulin may play a role in osteoblast functions such as collagen synthesis since insulin stimulated collagen levels at similar concentrations which stimulate NO production in UMR-106 cells.…”

“…The fact that NO may play an essential role in bone metabolism prompted us to explore insulin actions on NO system in UMR-106 cell (35) and we show that insulin has significant stimulatory effects on NO system. Insulin (1-100 nM) stimulated NO production in a dose-dependent manner, suggesting that NO production is through the insulin receptor activation since the insulin receptor tyrosine kinase is known to be activated at the insulin concentrations between 1 and 100 nM (36). The levels of NO produced by insulin in the UMR-106 cells are in the significantly lower range (approximately 3-6 M) as compared to those found in cytokine-mediated NO generation (over 30 M) (37).…”

Localization of Janus Kinase 2 to the Nuclei of Mature Oocytes and Early Cleavage Stage Mouse Embryos

“…Growth hormone, prolactin, insulin, and interferon gamma and their corresponding receptors have been reported to undergo internalization or endocytosis followed by translocation into the nucleus [44][45][46][47][48][49][50][51]. However, the downstream substrates of Jak2 are unknown.…”