The Expression,Effects And Mechanism Of Sterol Regulatory Element Binding Protein 1 (SREBP1) In Papillary Thyroid Carcinoma

Objective: Abnormal metabolic pathways exist in cancer cell supporting spcecial material and energy metabolism demand for its high need for rapid proliferation.The metabolic research on tumor-related fatty acid metabolism started and extended gradually from 1990 s.Tumor cells synthesis almost 90% of required lipids de novo,while most nomal cells get their fatty acid from circulation.Sterol Regulatory Element Binding Protein(SREBP1)is a key transcription factor regulating the way of fatty acid biosynthesis.SREBP1 acts as a primary regulator of lipogenic genes expression and overexpresses in a variety of malignant tumors,such as breast cancer,hepatocarcinoma and endometrial cancer.However,there is no research invoves in SREPB1 in thyroid cancer.Thyroid cancer is the common malignant endocrine tumor with a prevalence about 1.5% in the population,in which papillary thyroid cancer(PTC)accounts for almost 95%.Therefore,we detect the expression of SREBP1 in PTC and further explore its function and related mechanisms,expecting to provide new ideas for targeting therapy of PTC.Besides,we also carry out a preliminary research to find the expression of ACLY(ATP citrate lyase)and ACCA(Acetyl-Co A carboxylase),the fatty acid synthesis related genes and regulated by SREBP1,in order to enrich the research of SREBP1 in PTC.Methods: Tissue microarray and Immunohistochemical staining were used to detect the expression and cellular localization of SREBP1 in 95 PTC specimens and 28 paracarcinoma tissues;Real-time fluorescent quantitative reverse transcription polymerase chainreaction(RT-PCR)was used to detect the m RNA expression of SREBP1 in 40 pairs PTC and para-carcinoma tissues;Using Western Blot,we detected the expression of SREBP1 in 4 PTC cell lines(K1,IHH4,BCPAP and TPC-1)and 1 normal thyroid cell line(Nthy-ori3-1).Then we transfected specific si RNA(Small interfering RNA)to knockdown SREBP1 in TPC-1 and IHH-4 cell lines.Cell proliferation,cell apotosis,cell migrate and invision expriments were conducted to analyze the influence of si SREBP1 on cell biological behavior;RT-PCR and Western Blot were used to analyze the direct influence of si SREBP1 on the expression of ACLY,ACCA and FASN.Meanwhile,we used OIL RED O staining to detect triglyceride contant as a indirect influence of si SREBP1 on fatty acids synthesis.On the other hand,we treated PTC cell lines with m TOR inhibitor INK-128 to analysis its’ influence on the expression of SREBP1 and SREBP1 transcriptional genes.We also detected the influence of INK-128 on cell biological behavior and triglyceride contant.Moreover,we used RT-PCR,Western Blot and Immunohistochemical staining to detect the expression of ACCA and ACLY in PTC and para-carcinoma tissues.Results:(1)SREBP1 m RNA was highly expressed in PTC tissues compared with matched normal tumor-adjacent tissues(P<0.05);SREBP1 protein located mainly in both cytoplasm and nucleus of PTC tissues,and was upregulated in PTC tissues compared with normal tumor-adjacent tissues(P<0.001).(2)In PTC tissues,clinical association analysis revealed that elevated SREBP1 expression was significantly associated with large tumor size(≥2 cm),lymph node metastasis,advanced tumor stage(tumor-node-metastasis(TNM)stage III + IV)and extrathyroidal invasion(P<0.05).(3)Compared with control group,si SREBP1 reduced cell proliferation,migration,invasion and produces cell apotosis in TPC-1 and IHH-4 cell lines.si SREBP1 also reduced the expression of lipogenesis genes ACLY,ACCA,FASN,and the intracellular content of triglyceride(P<0.05).(4)TPC-1 and IHH-4 cell lines treated with m TOR inhibitor INK-128 can reduce the expression of endonuclear SREBP1 protein(SREBP1(m))and SREBP1 transcriptional proteins ACLY,ACCA and FASN,and reduce the intracellular triglyceride content.We also found reduced cell proliferation,migration and invasion ability in dosing group(P<0.05),but no significant change in cell apotosis(P>0.05).(5)ACCA protein was upregulated in PTC tissues compared with normal tumor-adjacent tissues(P<0.001),while the expression of ACLY protein had no significance between two groups(P>0.05).By analysing the IRS score of ACCA in PTC tissue with clinical features,we found that elevated ACCA expression was positivly associated with large tumor size(≥2 cm),lymph node metastasis,advanced tumor stage(tumor-nodemetastasis(TNM)stage III + IV)and extrathyroidal invasion(P<0.05).(6)By analysing the protein expression of ACCA and SREBP1,we found a positively correlation between their protin expression in PTC tissue(P<0.05).Conclusion:(1)SREBP1 is overexpressed in PTC,and can effect a change on biological characteristics and fatty acids synthesis of cancer cells.In PTC cell lines,m TOR pathway can regulate the expression of SREBP1.(2)ACCA is overexpressed in PTC,and is positive related with the expression of SREBP1 protein.The expression of ACLY is not significant different between PTC tissues and thyroid tissues.