Relationship Between Special Tubular Localization And Function Of MAP4K3 Protein

MAP4K3(mitogen-activated protein kinase kinase kinase kinase kinase 3)is a member of the Ste20 family of serine/threonine kinases.It is very conservative in evolution and has very high similarity with MAP4K2 protein.It has been shown that MAP4K3 plays an important role in cell growth,autophagy,cancer cell migration and associates with poor prognosis of cancer.In a recent study,we found that MAP4K3 protein shows tubular localization in some cells,while mainly cytoplasmic in other cells.And this difference in localization may be affected by LKB1.Therefore,we propose that the difference in MAP4K3 localization may be related to its function.We first confirmed the tubular localization of MAP4K3 in Hela cells and showed that ectopic expression of LKB1 in Hela cells can cause MAP4K3 localization change.At the same time,we observed in our experiments that overexpression of MAP4K3 in cells may have a negative impact on cell survival.By overexpressing MAP4K3 kinase dead mutant(MAP4K3-KD)and WT-MAP4K3 in cells,we found that under the same condition,the expression of MAP4K3-KD was higher,while the expression of WT-MAP4K3 was limited.Through further fluorescence detection,we found that MAP4K3-KD showed different localization pattern than WT-MAP4K3.Therefore,we speculated that there was a correlation between the specific localization of MAP4K3 and the kinase function.In order to further test whether the differential localization of MAP4K3 affects its protein function,we selected Hela cells with special MAP4K3 tubular localization and 293A cells without MAP4K3 protein tubular localization as models to verify whether the different localization of MAP4K3 affects its function in the amino acid activated mTOR signal pathway.However,contrary to predictions,we found that MAP4K3 does not affect the response of mTORC 1 to amino acids in either Hela or reported 293A cells.We further explored the role of MAP4K3 in autophagy and found that cells with tubular localization of MAP4K3 caused by LKB1 deficiency were less sensitive to amino acid starvation.When LKB1 expression was restored in Hela,the sensitivity to amino acid starvation also returned to a level comparable to that of cells without LKB1 deficiency.At the same time,we observed that both the deletion and overexpression of MAP4K3 promoted an increase in autophagic flux of cells.In general,the different localization forms of MPA4K3 correlats with their function in autophagy.It is of great significance to explore MAP4K3 related molecular pathways.