LPAR5 Promotes Papillary Thyroid Carcinoma Proliferation And Migration By Activating Class Ia PI3K Catalytic Subunit P110β

The incidence of thyroid cancer（TC）,the most common endocrine neoplasia,continues to rise.Today,surgical resection remains the foundation treatment for TC,the prognosis is very good.However,once thyroid cancer with lymph node metastasis,local recurrence or distant metastasis,the prognosis will be poor.In recent years,with the continuous progress of molecular biology and the gradual rise of the cognition of individualized therapy,targeted therapy has gradually become the hot spot of tumor therapy.Molecular targeted therapy has the advantages of high accuracy and less side effects.Searching for effective target genes and accurate individualized therapy has become the research hotspot of medicine.Lysophosphatidic acid receptor 5（LPAR5）,a member of the lysophosphatidic acid receptor family and has been demonstrated in a variety of malignancies.LPAR5,not only abnormally expressed in tumor tissues,is involved in mediating thyroid cancer progression,but the underlying mechanism needs to be further study.In this study,we confirmed that LPAR5 is upregulated in papillary thyroid carcinoma（PTC）especially in BRAF^V600E mutation PTC by analyzing TCGA database and performing immunohistochemistry assay in human thyroid cancer tissues.In order to further analyze its relationship with thyroid cancer proliferation and metastasis,and explore its possible regulatory mechanism.We treated LPAR5-specific antagonist TC LPA5 4 with different concentration gradients,and observed a concentration-dependent change in the proliferation capacity of CGTH-W3,TPC-1,B-CPAP and BHT-101 cells in vitro.According to Transwell assay,TC LPA5 4 can inhibit CGTH-W3and TPC-1 cells migration significantly（P<0.05）.In vivo,TC LPA5 4treatment could delay CGTH-W3 xenograft growth in nude mice.We also found that after the down-regulation of LPAR5,the changes of LPAR5 and downstream Akt proteins were detected by western blotting.It was found that after down-regulating LPAR5,the expression of Akt protein was significantly lower than that of blank control group（P<0.05）.LPAR5specific antagonists TC LPA5 4,PI3K inhibitor Wortmannin or m TOR inhibitor Rapamycin pretreatment abrogated phosphorylation of Akt and p70S6K1 stimulated by LPA in CGTH-W3 and TPC-1 cells,respectively（P<0.05）.Stimulating CGTH-W3 cells transfected with p EGFP-C1-Grp1-PH fusion protein by LPA resulted in the generation of phosphatidylinositol（3,4,5）-triphosphate,which indicates that PI3K was activated by LPA directly.The p110β-si RNA instead of p110α-si RNA transfection abrogated the increase of levels of phosphorylated Akt and S6K1 stimulated by LPA.Furthermore,immunoprecipitation assay confirmed an interaction between LPAR5 and p110β.Overall,in this study,downregulation of LPAR5 decreased the proliferation and migration phenotype via the PI3K/Akt pathway.Inhibition of LPAR5 or PI3K/Akt signal may be the novel therapeutic strategy for treating thyroid cancer.