HeLa细胞中激酶NUAK1调控Tuberiun的磷酸化

NUAK1是LKB1的下游激酶之一,可被LKB1磷酸化而激活,但对其在LKB1相关信号通路中的功能仍缺乏了解.本研究发现在HeLa细胞中重建LKB1表达后NUAK1与tuberin蛋白免疫共沉淀,提示在野生型LKB1存在时NUAK1与tuberin可能存在直接相互作用.进一步的激酶活性测定和in vivo蛋白磷酸化实验表明:在HeLa细胞中葡萄糖匾乏条件下,野生型LKB1可显著激活NUAK1的激酶活性；而被激活的NUAK1可明显提高tuberin 的磷酸化水平,使用NUAK1 siRNA pool干扰NUAK1的表达则几乎将tuberin的磷酸化水平降低为零.上述结果表明NUAK1可能介导了LKB1对tuberin磷酸化的调节,进而下调mTOR通路,抑制蛋白质合成与细胞生长增殖.

Kinase NUAK1 Regulating the Phosphorylation of Tuberin in HeLa Cells

As one of the downstream kinases of LKB1,NUAK1 is activated by the master kinase LKB1,yet the functions of NUAK1 in LKB1-related signaling have remained unclear.In the present study,NUAK1 co-immunoprecipitated with tuberin upon the restoration of LKB1 expression in LKB1-null HeLa cells suggesting a direct interaction between NUAK1 and tuberin in the presence of wild-type LKB1.In the following kinase activity and in vivo phosphorylation assays,a significant activation of NUAK1 kinase activity was observed in HeLa cells expressing wild-type LKB1 under glucose deprivation,and the activated NUAK1 kinase consequently enhanced the phosphorylation of tuberin by more than 3 folds;whereas the phosphorylation of tuberin was almost completely depleted by the interference of NUAK1 expression with siRNA pool.The above results suggested that LKB1 might regulate the phosphorylation of tuberin via the NUAK1 kinase,which is followed by the down-regulation of mTOR pathway and inhibition of protein syntheses and cell growth.