Wortmannin inhibits insulin-stimulated activation of protein phosphatase 1 in rat cardiomyocytes

Abstract

A major function of insulin in target tissues is the activation of glycogen synthase. Phosphatidylinositol 3-kinase (PI3K) has been implicated in the insulin-induced activation of glycogen synthase, although the true function of this enzyme remains unclear. Data presented here demonstrate that the PI3K inhibitors wortmannin and LY-294002 block the insulin-stimulated activation of protein phosphatase 1 (PP1) in rat ventricular cardiomyocytes. This loss of phosphatase activation mimics that seen in diabetic cardiomyocytes, in which insulin stimulation fails to activate both PP1 and glycogen synthase. Interestingly, in diabetic cells, insulin stimulated PI3K activity to 300% of that in untreated controls, whereas this activity was increased by only 77% in normal cells. PI3K protein levels, however, were similar in normal and diabetic cells. Our results indicate that PI3K is involved in the stimulation of glycogen synthase activity by insulin through the regulation of PP1. The inability of insulin to stimulate phosphatase activity in diabetic cells, despite a significant increase in PI3K activity, suggests a defect in the insulin signaling pathway that contributes to the pathology of insulin-dependent diabetes.

Interleukin-6 Impairs the Insulin Signaling Pathway, Promoting Production of Nitric Oxide in Human Umbilical Vein Endothelial Cells

“…It is thought that the phosphatase PP1 dephosphorylates Thr 495 , and inhibition of PP1 results in the hyperphosphorylation of Thr 495 , thus blunting eNOS activity. There is also evidence that insulin stimulates PP1 activity via a PI3-kinase-dependent pathway in rat cardiomyocytes (6). Interestingly, we observed that, in HUVECs, insulin stimulated PP1 activity, resulting in an increased dephosphorylation of Thr 495 .…”

“…Treatment with calyculin-A prevented the insulin-induced dephosphorylation of Thr 495 (data not shown). Insulin has been shown to activate PP1 via a PI3-kinase-dependent pathway in rat cardiomyocytes (6). Therefore, we tested whether insulin would also increase PP1 activity in HUVECs and whether IL-6 would affect insulin-stimulated PP1 activation.…”

TNF-α Downregulates Inhibitory Neurotransmission through Protein Phosphatase 1-Dependent Trafficking of GABAAReceptors

“…However, PI3K can also control PP1 activity (Ragolia and Begum, 1998;De Luca et al, 1999), suggesting that it can indirectly lead to receptor dephosphorylation. Using several experimental approaches, we identified PP1 as a mediator of TNF␣-dependent GABA A R trafficking in cultured hippocampal neurons and acute hippocampal slice CA1 pyramidal neurons.…”

Protein Phosphatase 2A Inhibitors, I1PP2A and I2PP2A, Associate with and Modify the Substrate Specificity of Protein Phosphatase 1

“…In cells, PP1 activity appears to be stimulated in response to insulin and other mitogens (45)(46)(47). Some of these physiological stimuli also lower PP2A activity (48 -53), perhaps contributing to the activation of the mitogen-regulated protein kinases cascade and to the promotion of cell proliferation (27).…”