Regulation of ploidy and senescence by the AMPK-related kinase NUAK1

Abstract

Senescence is an irreversible cell-cycle arrest that is elicited by a wide range of factors, including replicative exhaustion. Emerging evidences suggest that cellular senescence contributes to ageing and acts as a tumour suppressor mechanism. To identify novel genes regulating senescence, we performed a loss-of-function screen on normal human diploid fibroblasts. We show that downregulation of the AMPK-related protein kinase 5 (ARK5 or NUAK1) results in extension of the cellular replicative lifespan. Interestingly, the levels of NUAK1 are upregulated during senescence whereas its ectopic expression triggers a premature senescence. Cells that constitutively express NUAK1 suffer gross aneuploidies and show diminished expression of the genomic stability regulator LATS1, whereas depletion of NUAK1 with shRNA exerts opposite effects. Interestingly, a dominant-negative form of LATS1 phenocopies NUAK1 effects. Moreover, we show that NUAK1 phosphorylates LATS1 at S464 and this has a role in controlling its stability. In summary, our work highlights a novel role for NUAK1 in the control of cellular senescence and cellular ploidy.

A new role of NUAK1: directly phosphorylating p53 and regulating cell proliferation

“…To compare the phosphorylation of p53 between NUAK1-expressing and kinase-dead mutantexpressing cells, A549 cells stably transfected with LKB1 (WT) or vector control were transiently transfected with NUAK1, T211A or kinase-dead mutant and treated under glucose starvation for 2 h. In the presence of LKB1 (WT), transfection of WT NUAK1 significantly upregulated phosphorylation of p53 at Ser15 and Ser 392, but no upregulation was observed when cells were transfected with kinase-dead mutant K84A (Figure 3b). Moreover, compared with vector control or T211A mutant, p53 phosphorylation was clearly decreased by kinase-dead mutant, which is consistent with the report that K84A mutant acts as a dominant-negative form of NUAK1 (Humbert et al, 2010).…”

“…However, NUAK1 was also reported to be phosphorylated and activated by major tumor suppressor LKB1 (Lizcano et al, 2004). Little research has been done on the role of this kinase under the regulation of LKB1, until it was recently demonstrated that NUAK1 regulated cell senescence and ploidy in the presence of LKB1, which suggests that NUAK1 has a novel tumor suppressive function in LKB1-related signaling (Humbert et al, 2010).…”

“…In normal human diploid fibroblast WI-38 cells, NUAK1 is suggested to regulate senescence by a mechanism that does not involve p53 (Humbert et al, 2010), which is not consistent with our findings for p53 and p21/WAF1 in A549 or G361 cells and also conflicts with earlier reports that have suggested that the p53 pathway is involved in regulation of senescence in normal human cells (Gil et al, 2004;Herbig et al, 2004). Results from Humbert et al (2010) also have shown that, depending on the cell type, the aneuploidy induced by NUAK1 might have different consequences: senescence or cell death.…”

“…These results lead to an apparent paradox that, although NUAK1 is phosphorylated and activated by the major tumor suppressor LKB1, the role it plays is mainly in tumor cell survival and progression. A very recent study has elucidated a novel function of NUAK1 in the control of cellular senescence and ploidy, which suggests that NUAK1 also possesses tumor suppressive properties (Humbert et al, 2010).…”

The SCN9A channel and plasma membrane depolarization promote cellular senescence through Rb pathway

“…Nevertheless, a growing body of evidence supports the involvement of other pathways in the regulation of senescence, and in particular, in that of oncogene‐induced senescence (OIS) (Bianchi‐Smiraglia & Nikiforov, 2012; Christoffersen et al., 2010; Cipriano et al., 2011; Humbert et al., 2010; Lin et al., 2010; Scurr et al., 2010). …”