Study the regulatory mechanism of Sp1 on T-cell lymphoma Invasion and Metastasis 2 (TIAM2) expression in Hepatocellular Carcinoma

Abstract

T-cell lymphoma invasion and metastasis 2 (TIAM2) is the homologue of TIAM1 which is known as guanine nucleotide exchange factor (GEF) TIAM1 is associated with many types of malignancies Our previous study showed that TIAM2S one of the TIAM2 isoforms is normally expressed only in the human brain but found aberrant expressed in hepatocellular carcinoma (HCC) Although results from clinical specimen cellular and animal models showed that TIAM2S functions as an oncogene in the tumorigenesis of liver cancer the regulatory mechanisms of TIAM2S and its pathological function remains largely unknown TIAM2S was predicted as a TATA-less gene which containing a GC-box (GGGGCGGGG) located in TIAM2S promoter region Sp1 is a transcription factor that binds to GC-rich motifs and involved in a wide range of cellular processes as well as tumorigenesis in many types of cancers We hypothesized that Sp1 may bind to TIAM2S promoter and regulate TIAM2S expression in HCC cells The aim of this study is to examine whether ectopic expression of TIAM2S in liver cancer cells is mediated by Sp1 Here we have performed EMSA and chromatin immunoprecipitation assay (ChIP) to confirm that Sp1 specifically binds to TIAM2S prompter region To investigate whether Sp1 regulates TIAM2S gene expression TIAM2S prompter assay were conducted Indeed TIAM2S core promoter was activated in HCC cell lines and the effect was more significant under Sp1 overexpression Moreover Endogenous TIAM2S expression correlates closely with levels of Sp1 Overexpression and knockdown of Sp1 in different HCC cell lines resulted in changing the TIAM2S mRNA levels thus reflected that Sp1 specifically regulates human TIAM2S transcription Recent studies showed that phosphorylation of Sp1 at T379 increase its transcriptional activity and is involved in tumorigenesis Thus we also examine whether phosphorylation of Sp1 at T379 affects TIAM2S expression in liver cancer cells The results showed that TIAM2S mRNA level is not significantly changed between wild type and mutant T379 of Sp1 protein Moreover 70% (42/60) of HCC biopsies showed increases in the Sp1 level in the tumors and the pattern is correlated with TIAM2S In this study we have illustrated the important role of Sp1-mediated TIAM2S expression in HCC cells and it will help to develop new therapeutic strategy for the treatment of HCC

Date of Award	2014 Aug 28
Original language	English
Supervisor	Hsiao-Fang Sun (Supervisor)