Roles Of LOXL4 In Hepatocellular Carcinoma And Reserch On Its Molecular Mechanisms

Tumor cells are regulated by tumor microenvironment,which is composed of stromal cells and extracellular matrix(ECM).Extracellular matrix is the main component of tumor microenvironment and plays a vital role in tumor metastasis.The extracellular matrix proteins are important components of the tumor microenvironment and play important roles in the initiation and progression of tumors.Lysyl oxidases(LOXs)belong to ECM protein,and it has been showed that LOXs can promote tumor invasion,metastasis and proliferation.LOXs promote tumor invasion and metastasis mainly though activation of FAK/Src pathway and epithelial-mesenchymal transition(EMT).Lysyl oxidase-like 4(LOXL4)belongs to the lysyl oxidase family of secreted enzymes involved in ECM crosslinking.Overexpression of LOXL4 gene is associated with a variety of human malignancies.However,its biological functions and clinical significance in hepatocellular carcinoma(HCC)remain unknown.First of all,we demonstrated that LOXL4 was significantly up-regulated in HCC tissues and its expression level was closely correlated with cancer metastasis and patient prognosis.Overexpression of LOXL4 dramatically promoted HCC cell migration and invasion in vitro and intrahepatic metastasis in vivo.Knockdown of LOXL4 dramatically suppressed HCC cell migration and invasion in vitro.However,LOXL4 has no obvious effects on HCC cell proliferation.Then we examined the role of LOXL4 in regulation of FAK/Src signaling pathway,and found that LOXL4 can activate the FAK/Src signal pathway to enhance cell-matrix adhesion,which promoted migration and invasion of HCC cells.LOXL4 appears in exosome,which plays an important role in cell communication.We wondered whether exosome-mediated secretion of LOXL4 has effects on HCC cells and other target cells.We used exosomes derived from HCC cells to treat HCC cells and human umbilical vein endothelial cells(HUVEC),and found that LOXL4 could promote migration of HCC cells and angiogenesis in the form of exosome.Only the members that contain SRCR domain appear in exosome among the LOX family,thus we hypothesized that the appearance of LOXL4 in exosome may be associated with the SRCR domain.In order to confirm this hypothesis,we constructed the LOXL4 and deletion mutants and examined them in the corresponding exosomes.The results showed that SRCR domain deletion mutants can not enter exosome,just as another LOX subfamily without SRCR domain.In order to find the proteins that may interact with the SRCR domain in the procession that LOXL4 enters into exosome,we used immunoprecipitation(IP)to find out the proteins,followed by mass spectrometric analysis and co-immunoprecipitation(Co IP).The work is ongoing and need to be further studied.Taken together,these data provide substantial new evidence that LOXL4 is involved in cancer cell invasion and indicate that LOXL4 may serve as a novel prognostic marker and therapeutic target for HCC.