Investigation of role that LKB1 Ser431 phosphorylation and Cys433 farnesylation play by mouse knock-in analysis reveals an unexpected role of prenylation in regulating AMPK activity

The LKB1 tumour suppressor protein kinase functions to activate two isoforms of AMP-activated protein kinase (AMPK) and 12 members of the AMPK-related family of protein kinase. The highly conserved C-terminal residues of LKB1 are phosphorylated (Ser431) by PKA and RSK and farnesylated (Cys433) within a CAAX motif. To better define the role that these posttranslational modifications play, we created homozygous LKB1S431A/S431A and LKB1C433S/C433S knock-in mice. These animals were viable, fertile and displayed no overt phenotypes. Employing a farnesylation-specific monoclonal antibody that we generated, we establish by immunoprecipitation that the vast majority, if not all, of the endogenous LKB1 is prenylated. Levels of LKB1 localised at the membrane of LKB1C433S/C433S liver and fibroblasts were substantially reduced compared to wild type mice, confirming that farnesylation plays a role in mediating membrane association. Whilst AMPK was activated normally in the LKB1S431A/S431A animals, we unexpectedly observed in all tissues and cells derived from in LKB1C433S/C433S mice examined that basal as well as AMPK activation induced by the AMP-mimetic AICAR, phenformin as well as muscle contraction was significantly blunted. This resulted in reduced ability of AICAR to inhibit lipid synthesis in primary hepatocytes isolated from LKB1C433S/C433S mice. Activity of several AMPK-related kinases analysed (BRSK1, BRSK2, NUAK1 SIK3 and MARK4) was not affected in tissues derived from LKB1S431...
Source: BJ Signal - Category: Biochemistry Authors: Tags: BJ Signal Source Type: research