Investigating The Molecular Mechanisms Of Lung Cancer By Using New Genetically Modified Mouse Models

Lung cancer is the most common and one of the most deadly cancers worldwide.Lung adenocarcinoma(ADC)and squamouse cell carcinoma(SCC)are the two prevalent types of lung cancer.The etiology and pathogenesis of lung cancer is complex and has not been fully elucidated.Although the genomic alterations of human lung SCCs have been identified,little is known about the genetic alterations that initiate lung SCCs.Furthermore,the lack of genetically modified mouse models for SCCs severely hinders the understanding of molecular mechanisms and the development of new drugs.In this study,we generated new genetically modified mouse models for SCCs and ADC to explore the functions and molecular mechanisms of TGF-?signaling pathway and EZH2in lung tumorigenesis and progression.TGF-?ligands bind to TGF-?receptors on the membrane and trigger responses via canonical SMAD and non-SMAD signaling pathways.Previous studies have revealed the dysfunction of TGF-?signaling pathway could initiate a wide range of epithelial tumors.Whether TGF-?signaling alterations could act as a driver to initiate lung SCC and contribute to lung SCC progression is not yet clear.Here,we analyzed the human lung SCC data from The Cancer Genome Atlas(TCGA)database,and found that the deletion of TGFBR2 and SMAD4 genes were common in human lung SCC samples,and its low expression was associated with poor prognosis.In a well-established ADC mouse model iuduced by Kras^G12D,Tgfbr2 loss altered the subtype of lung cancer and led to the SCC formation.Of note,metastatic lesions of SCC were observed in the mediastinal lymph nodes,heart atriums and kidneys.In another well-established lung adenocarcinoma mouse model caused by Kras^G12D expression and p53 loss,concurrent Tgfbr2 loss also initiated metastatic lung SCCs.Moreover,the lung SCCs induced by Tgfbr2 loss exhibited the typical molecular alterations implicated in human lung SCCs including activation of Akt,EGFR and STAT3,as well as upregulation of p63,cyclin D1,SPP1 and CD44.Mechanistically,we revealed that SMAD4-dependent classical signaling cooperated with non-classical ERK1/2 to impede the expression of SOX2 and TP63.Collectively,we demonstrated an important role of TGFBR2 in suppressing lung SCC formation and provided two mouse models of metastatic lung SCCs for further exploring the underlying mechanisms and potential therapeutic targets.Ezh2(enhancer zeste homolog 2)represses the transcription of target genes by methylating Lys27 of histone H3(H3K27).A previous study has shown that Ezh2 acts as an oncogene in lung ADC development and its overexpression alone is able to initiate lung ADCs.However,we found that deletion and mutations of EZH2 were also frequently present in human lung ADC samples,with 14%of patients harboring loss-of-function EZH2 alterations.Consistently,Ezh2 loss dramatically promoted Kras-driven ADC formation in the mice.Kras^G12D/+;Ezh2^fl/fl mice exhibited shorter lifespan,more tumor lesions and higher tumor burden than Kras^G12D/+mice,suggesting the tumor-suppressive role of Ezh2 in Kras-driven ADCs.Mechanistically,Ezh2 loss amplified Akt and ERK activation through de-repressing its target insulin-like growth factor 1(Igf-1).Additionally,Ezh2 loss exacerbated the inflammatory response of Kras-driven ADC,thereby promoting the initiation of lung ADCs.Taken together,our findings revealed the tumor suppressive function of Ezh2 in Kras-driven ADCs,underlining the importance of revaluating the application of EZH2 inhibitors in a variety of cancers.