The Gene Lass2 Inhibit Tumor Metastasis

The low extracellular pH(pHe)can enhance tumor metastasis through inducing the increase of the secretion of proteases and enhancing the activation of the relevant proteases either in intracellular vesicles or in extracellular environment.It has been described that proton pump V-ATPases(vacuolar H⁺-ATPase)have an important role in regulating the pHe and intracellular pH(pHi)of tumor cells and maintaining the acidic-microenvironment of cancer cells.As the subunit of V-ATPase complex, ATP6L(c subunit)plays a key role for activity of V-ATPase because of ATP6L providing proton hydrophilic transmembrane path.We previously identified the full-length cDNA Of LASS2(Homo sapiens longevity assurance homologue 2 of yeast LAG1,GenBank acc.no.NM₀22075) and found that LASS2 interacted with ATP6L through yeast two-hybrid screening and GST-pull down assay.LASS2 is also designated as TMSG-1(Tumor metastasis-suppressor,GenBank acc.no.AF189062).The LASS2/TMSG-1 expression was low in highly metastatic cancer cells by RT-PCR analysis.In this study,northern analysis further validated that the level of LASS2 mRNA was lower in a human hepatocellular carcinoma cell line with highly metastatic potential(HCCLM3)than that in the HCCLM3 parent cell line with lowly metastatic potential(MHCC97-L),and lower in clinical hepatocellular carcinoma group with metastasis than that in clinical hepatocellular carcinoma group without metastasis.Meantime,the migration,the adhesion and invasion of HCCLM3 cells were suppressed in vitro when LASS2 was overexpressed in HCCLM3 cells. Moreover,we also precisely confirmed that LASS2 interacted with ATP6L by co-immunoprecipitation(co-IP),protein subcellular colocatlization and fluorescence resonance energy transfer(FRET)assay.The result of fluorescence recovery after photobleaching(FRAP)analysis also indicated that LASS2 could inhibit ATP6L moving.After LASS2 was overexpressed in HCCLM3 cells,the secretion and activation of MMP-2 and the phi recovery from NH₄Cl-prepulsed acidification were inhibited.It is interesting,through acridine orange staining,we observed that lysosomes' moving under acidic microenvironment stress was inhibited when LASS2 was overexpressed in HCCLM3 cells.The impressive effect of LASS2 overexpression was remarkable inhibition of the highly metastatic ability of HCCLM3 cells in vivo.In conclusion,our data suggest that LASS2 is involved in the control of cancer metastasis via interacting with ATP6L,a subunit of proton pump V-ATPase.