The Molecular Mechanism Of Fli-1Promotes Development Of Small Cell Lung Cancer Through Regulating TGFβ/smad Signaling Pathway

The molecular mechanism of Fli-1promotes development of smallcell lung cancer through regulating TGFβ/smad signaling pathwaySmall cell lung cancer (SCLC) is regarded as the most malignanttumor in all types of lung cancers, accounts for approximately15%-20%.Small cell lung cancer shared common characteristics of short populationdoubling time, high invasion and recurring, and sensitivity toradiotherapy and chemotherapy. The five-year survival of small cell lungcancer is10%for extended stage and2%for limited stage because manypeople are diagnosed at extended stage, limited stage were found only inabout one-third of patients. In the last two decades, there is littleprogression on treatment of small cell lung cancer. Although patientswith small cell lung cancer are sensitive to initial treatment, most patientsare going to be recurrent or progressive and due to die. It has been amajor research subjects to improve the therapeutic effects of small celllung cancer. Molecular targeting therapy have been successful in manykinds of tumor treatment, but failed in small cell lung cancer because themechanism of disease is unclear. Therefore, the molecular pathogenesisof small cell lung cancer is need to confirm further which should proceedwith analyzing of abnormal expression of oncogene proteins andexploring more appropriate molecular targets, which may bring breakthroughs to treatment of small cell lung cancer.Research background:Fli-1(Friend leukemia virus integration1) is an Ets (E26transformation-specific) transcription factor family member, was firstidentified as a target of proviral integration in F-MuLV-induced mouseerythroleukemia by Ben-david. As a transcription factor, Fli-1couldcombined with many the promoter regions and enhancers of the gene, orregulated transcription through protein-protein interaction. Under thephysiological conditions, Fli-1is mainly expressed on blood stem cellsand endothelial cells and plays an important regulatory role in endothelialcells growth. In the preceding work of our project group, we found Fli-1could promoted cell growgh inhibited and cell death. The study alsorevealed that SHIP-1is a direct target of Fli-1. The overexpression ofFli-1inhibited SHIP-1activities and induced erythroleukemiaprogression. These study show Fli-1play an oncogene role in tumorgeneration and development, may be a good therapeutic target. On solidtumor side, Fli-1was presented in almost90%Ewing sarcoma asEWS/Fli-1fusion gene, which directly contribute to cell transforminginto malignancy, then led to Ewing sarcoma. In recent years, our andothers study results showed Fli-1was high expressed in melanomas,breast cancer, ovarian cancer and colorectal cancer. However, the specificbiological functions of Fli-1in solid tumor and molecular mechanism of Fli-1remains unknown. Studies towards elucidating the mechanisms ofFli-1regulating tumor generation and development depends onidentification of the signaling pathway and target genes, However, weknew very little about it, and pressing need further deeper exploration andresearch.Research objectives:1. Screen the expression pattern of Fli-1in solid tumor.2. Analyze the correlation between the expression level of Fli-1andclinical data.3. Complete assess the function of Fli-1in generation and development ofsmall cell lung cancer.4. Discuss the mechanism of Fli-1promotes cancer, clarify the signalpathway and target genes regulated by Fli-1.Research method:Screen the expression pattern of Fli-1in solid tumor usedimmunohistochemical staining, especially in small cell lung cancer.Analyze the correlation between the expression level of Fli-1and clinicaldata by statistical method. Down-regulation of Fli-1by small interferingRNA (siRNA), MTT, cell count, flow cytometry, Annexin V/PI stain,Transwell and soft gar assay were used to assess the affection of Fli-1incell growth, cell cycle, apoptosis, migrate and ability of colony forming.Establish NCI-H446cell model of stable interference Fli-1with retrovirus to study the impact of Fli-1on tumor formation in nude mice atwhole animal level. CO-IP(Co-Immunoprecipitation), luciferase reporterassay, western blot and RT-PCR methods were used to discuss themechanism.Research result:1. Fli-1was expressed in multiple tumors, and small cell lung cancer isthe most significant. The expression level of Fli-1was correlated withtumor stage.2. Fli-1played a role of promote cell growth, cell cycle, colony formingand inhibit cell apoptosis, illustrated Fli-1have important function intumor initiate, formation and malignant phenotype maintain.3. On the whole animal level, Fli-1could significantly inhibited in vivotumorigenic ability.4. Fli-1interacts with Smad3and could significantly inhibited activity ofSmad3.5. Fli-1could inhibited phosphorylation of Smad3but do not affectbackground level of Smad3.6. Fli-1regulated the transcriptional activity of Smad3target genes andthe TGF-β/smad signal pathway.Research conclusions:This study completed the research on gene function of Fli-1at thecellular level, molecular level and animal level and revealed Fli-1could promote cell proliferation and colony forming ability and inhibitapoptosis as a cancer-promoting gene in small cell lung cancer. Weexplored molecular mechanism and demonstrated that Fli-1interacts withSmad3and inhibited its activity and the transcriptional activity ofdownstream target genes, and then involved regulation of TGFβ cellularsignal transduction pathway. Therefore, this research contributed tofurther understanding the molecular mechanism involved in tumorgeneration and development and provide new powerful clue forthoroughly research of TGF-β/smad signal pathway. Addition, our studyalso provided theoretical and experimental base for molecular targettherapy which specifically target Fli-1in small cell lung cancer.