Mechanism Of PTGES/PGE₂ Signaling In Lung Cancer Metastasis

Early metastasis and local recurrence are the major causes of mortality and poor prognosis of non-small cell lung cancer(NSCLC).Generally,tumor metastasis is affected by two factors:the metastatic features of the tumor cells themselves,and the promotion of tumor microenvironment.However,due to lack of a relevant animal model for characterization,the underlying mechanism remains elusive.Lung tumor suppressor gene Gprc5a-knockout(ko)mice are susceptible to lung inflammation,tumorigenesis and metastasis,which resembles the pathological features in human patients.This study used this model to systematically study lung metastasis.In the first part,we showed that PTGES/PGE₂ signaling was highly associated with lung tumorigenesis and metastasis in Gprc5a-ko mice.Dysregulated PTGES was essential for the promotion of tumor migration and metastasis of NSCLC cells.Knockdown of PTGES in lung cancer cells resulted in suppressed cell migration,which was reversed by exogenous PGE₂.Consistent with this,PTGES knockdown also reduced the expression of CSC markers,tumor sphere formation,colony forming activity,tumorigenicity,and lung metastasis in mice model.Dysregulated PTGES is mainly attributed to protein stabilization by USP9X,a deubiquitination enzyme.USP9X physically interacted with PTGES and prevented it from proteasome-directed degradation via deubiquitination.In support,USP9X expression was highly correlated with PTGES expression in NSCLC tumor tissues.In the second part,we aimed to investigate the roles of the PTGES/PGE₂ pathway in lung cancer progression.Interestingly,Ptges-knockout in mouse lung tumor cells,although reduced their stemness and EMT-like features,still formed tumors and lung metastasis in immune-deficient nude mice,but not in immune-competent mice(C57 mice).Suppression of PTGES in lung tumor cells reduced the resistance to T cell-mediated cytotoxicity in vitro.This suggested that PTGES/PGE₂ signaling-mediated anti-T cell action plays a key role in promoting lung cancer metastasis.PGE₂ induced tumor-associated macrophage polarization and inhibits T cell function by inducing cytokines such as G-CSF to recruit bone marrow-derived suppressor cells(MDSCs).Importantly,the Ptges/PGE₂ pathway was significantly increased in the lung tissue of Gprc5a-ko mice,which was closely related to the increased lung metastasis in this model.Inhibitors of PTGES(Cay10526)could reduce tumor metastasis in Gprc5a-ko mice.Mechanistically,PTGES/PGE₂signaling was essential for suppression of innate and adaptive immunity.IHC staining showed that active PTGES was inversely correlated with CD8+T cells infiltration in human NSCLC samples.GPRC5A expression was highly negative correlated with PTGES expression in NSCLC tumor tissues.In summary,this study utilized the Gprc5a-ko mouse model to reveal and explain two important mechanisms of the PTGES/PGE₂ pathway in promoting lung metastasis:1.Tumor cells promoted themselves to metastasize,including enhancing cell stemness and resist T cell-induced cytotoxicity;2.Tumor cells induced immunosuppressive effects in the microenvironment,including recruitment of immunosuppressive cells(MDSC),and induction of macrophage polarization.Therefore,in inflammatory lung tissue,targeting PTGES/PGE₂can re-establish immunity and inhibit lung metastasis.