Thesis:ifngamma Induces CD47 And PD-L1 Expression And The Function And Mechanism Of PD-L1 LncRNA Splice Isform In The Development Of Lung Cancer

Cancer is one of the major threats to human health worldwide and brings huge social medical costs.The incidence and mortality of lung cancer are on the rise due to the aging of population and the adoption of new unhealthy lifestyle behaviors.At present,in addition to traditional surgical treatment,radiotherapy and chemotherapy,immunotherapy has become the current development trend of tumor treatment with its high specificity and low side effects.Among these intrinsic negative check-points,programmed death protein 1(PD-1)and its ligand 1(PD-L1)are a prominent pair,the blockade of which has proven to be a successful immune-therapeutic strategy to treat cancer.As a new immune checkpoint molecule,CD47 binds to SIRPα on the phagocyte surface and initiates inhibitory signaling to prevent phagocytosis of tumor cells by phagocytes.Exploiting CD47-SIRPα signaling has been proven to be an effective way for cancers to evade immune attack by phagocytes.Although using a blockade of check-point shows great promise in tumor immunotherapy,the immune-checkpoint inhibition strategy is limited for patients with solid tumors.The mechanism and efficacy of such immune-checkpoint inhibition strategies in solid tumors remains unclear.By immunohistochemical staining,we screened more than 275 human LUAD samples and their paired distal non-cancerous tissues samples and we found that the majority of lung cancer samples were PD-L1-negative,with little or no PD-L1 protein expression.To explore the mechanism underlying the varied PD-L1 protein expression in LUADs across various stages,we assessed the PD-L1 m RNA level in PD-L1 protein-positive or PD-L1 protein-negative lung cancer tissues.Interestingly,we found that,in addition to PD-L1 m RNA,the PD-L1 gene in human LUAD can generate a long non-coding RNA(PD-L1-lnc)through alternative splicing.Moreover,in a similar manner to PD-L1 m RNA,PD-L1-lnc in LUAD is markedly upregulated by IFNγ.Once generated,PD-L1-lnc promotes LUAD cell proliferation and invasion but decreases cell apoptosis via directly binding to c-Myc and activating c-Myc transcriptional activity.Taken together,in part one,we identify the PD-L1-lnc-c-Myc axis as a novel mechanism underlying human LUAD progression.In part two,we explored the mechanisms underlying CD47/PD-L1 upregulation and its role in lung adenocarcinoma metastasis.By examining human lung adenocarcinoma samples,some which were metastatic or subjected to chemotherapy,and the paired adjacent normal lung tissue,we explored the correlation between lung adenocarcinoma CD47/PD-L1 levels and cancer metastasis or chemotherapy treatment.We found that human lung adenocarcinoma CD47/PD-L1 levels were markedly increased following cancer metastasis or chemotherapy treatment.CD47/PD-L1 upregulation was induced by IFNγ,the level of which was concurrently elevated in the tumor microenvironment after tumor metastasis or chemotherapy treatment.Supporting this,IFNγ receptor(IFNγR)was expressed in human lung adenocarcinoma tissues regardless of their CD47/PD-L1 protein expression.CD47/PD-L1 expression in various lung cancer cells was markedly increased by IFNγtreatment.Mechanistically,IFNγ promoted CD47/PD-L1 expression by activating interferon regulatory factor-1(IRF1),which bound to an IRF1-binding domain within the CD47/PD-L1 promoter region and subsequently increased CD47 transcription.Functionally,IFNγ-enhanced CD47 expression facilitated human lung cancer cell invasion both in vitro and in vivo,whereas IFNγ-induced CD47 upregulation and cancer metastasis were blocked by mutating the IRF1-binding site within the CD47 promoter.The promotive effects of IFNγ on human lung adenocarcinoma CD47 expression and cancer metastasis were further validated in athymic BALB/c nude mice implanted with human lung cancer cells.In the present study,we reported that the PD-L1 gene can generate a long non-coding RNA through alternative splicing to promote lung adenocarcinoma progression by enhancing c-Myc activity.We also found that CD47 upregulation induced by IFNγ is positively associated with tumor metastasis.Our study identifies an IRF1-binding domain within the CD47 promoter region and shows that IFNγ,whose level in the TME is elevated following tumor metastasis or chemotherapy,can promote CD47 expression by activating IRF1.Our results argue in favor of investigating PD-L1-lnc depletion in combination with PD-L1 blockade in lung cancer therapy;our results reveal that human lung adenocarcinoma can exploit IFNγto upregulate CD47 expression during metastasis and chemotherapy treatment.