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  • Title: Post-translational regulation of PTEN catalytic function and protein stability in the hibernating 13-lined ground squirrel.
    Author: Wu CW, Bell RA, Storey KB.
    Journal: Biochim Biophys Acta; 2015 Nov; 1850(11):2196-202. PubMed ID: 26189697.
    Abstract:
    BACKGROUND: The insulin signaling pathway functions as a major regulator of many metabolic and cellular functions, and has been shown to be reversibly suppressed in many species during hibernation. This study characterized the regulation of PTEN phosphatase, a negative regulator of the insulin receptor network, over the torpor-arousal cycle of hibernation in the skeletal muscle of Ictidomys tridecemlineatus. METHODS: Western blotting and RT-PCR were used to analyze post-translational and transcriptional regulations of PTEN respectively. Enzymatic activities were determined by the malachite green assay, while protein stability was assessed the using pulse-proteolysis method. RESULTS: During torpor, the ratio of non-phosphorylated PTEN (S380/T382/T383) was significantly elevated by 1.4-fold during late torpor compared with euthermic controls; this was coupled with an increase in substrate affinity for PIP3 (by 56%) in late torpor. Two proteolytic cleavage PEST motifs were identified in the C-terminus that overlapped with the phosphorylation sites of PTEN; pulse-proteolysis analysis of PTEN protein showed a decrease in protein stability during late torpor (Cm of urea decreased by 21%). Furthermore, the increase in PTEN activity observed was correlated with a decrease in PDK-1 phosphorylation by 32%, suggesting a downstream effect of PTEN activation during torpor. Transcriptional analysis showed that mRNA expression of pten and pdk-1 remain unchanged during hibernation, suggesting post-translation modification as the primary regulatory mechanism of PTEN function. CONCLUSION: Phosphorylation plays an important role in the regulation of PTEN enzymatic activity and protein stability. GENERAL SIGNIFICANCE: Activation of PTEN during torpor can regulate insulin signaling during periods of low energy state.
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