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[摘要]：Adipose LPL (lipoprotein lipase) plays an important role in regulating plasma triacylglycerols and lipid metabolism. We have previously demonstrated that PKC alpha (protein kinase C alpha) depletion inhibits LPL translation in 3T3-F442A adipocytes. Using in vitro translation experiments, the minimum essential region on the 3'UTR (3'-untranslated region) of LPL mRNA required for the inhibition of translation was identified as the proximal 39 nt. These results were confirmed by RNase protection analysis using cytoplasmic proteins isolated from the adipocytes treated with PKC alpha antisense oligomers and the LPL 3'UTR transcript (LPL 3'UTR nt: 1512-1640). The protein components involved in this RNA-binding interaction from PKCa depletion were passed through an affinity column containing a sequence of the LPL 3'UTR and, after Western blotting, the RNA-binding proteins were identified as the catalytic and the regulatory subunits of PKA (protein kinase A), C alpha and RII beta and AKAP (A-kinase-anchoring protein) 121. This RNA inhibitory complex consisted of the same RNA-binding proteins that have been identified previously as mediators of LPL translational inhibition by PKA activation, suggesting that PKC alpha depletion inhibits LPL translation through PKA activation. In additional experiments, PKC depletion by prolonged PMA treatment or PKC alpha antisense oligomers resulted in an increase in PKA activity in 3T3-F442A adipocytes, comparable with PKA activation with adrenaline (epinephrine) treatment. These results demonstrate that LPL translational inhibition occurs through tin RNA-binding complex involving PKA subunits and AKAP121, and this complex can be activated either through traditional PKA activation methods or through the depletion of PKC alpha. |
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