Effects Of Plasmid-Based SiRNA-Stat3and GRIM-19on Human Thyroid Carcinoma Cell Growth

Thyroid cancer is the most common malignant tumors of the endocrine system.Although the majority of the patients can be cured with surgery, radioiodine, Thyroxinetherapy, about15%of patients can not be cured because of poorly differentiated andinfiltrating tumor growth.Medullary, undifferentiated and squamous cell carcinomas of thethyroid are often found distant metastases,and not sensitive to radiotherapy andchemotherapy. In addition, reoperation of recurred tumors will increased surgical difficultyand the possibility of complications. Therefore,it is necessary to explore a new treatmentto improve prognosis.Stat3is an important member of JAK-Stat3signaling pathway,which has been found toplay a key role in promoting differentiation,antiapoptosis, proliferation and cell cycleprogression. Persistent activation of Stat3and its abnormal expression have been detected inmany kinds of human tumors, and have been shown to be associated with thyroid cancerprogression. Thus,Stat3may be a potential molecular target for RNA intervention onthyroid cancer. However,in mammalian cells,RNAi can not completely suppress geneoverexpression, owing to the idiosyncrasies associated with shRNAs and their target genes.In order to seek a better therapeutic regimen,we have developed a plasmid co-expressedsiRNA-Stat3and GRIM-19.Objective: To investigate the effects of co-expressed plasmids containing siRNA-Stat3and GRIM-19on human thyroid carcinoma growth in vitro.Methods: The thyroid carcinoma cell line,SW579,were transfected withplasmids:psi-Scramble、psi-Stat3、pGRIM-19and pGRIM-19-si-Stat3. mRNA and proteinlevels of Stat3、GRIM-19、Bcl-2and MMP9were detected by RT-PCR and Western blot.MTT assay was used to determine the proliferation inhibition of cells. Wound-healing assaysand Transwell test were applied to detect migration and invasion.Results: The psi-Stat3、pGRIM-19,and pGS groups show that the total Stat3、Bcl-2and MMP9expression levels were obviously reduced, and the expression of GRIM-19wassignificantly increased. MTT assay demonstrated that the pGS group showed remarkableproliferation inhibition compared to pSi-Stat3and pGRIM-19groups. The results of Wound-healing assays and Transwell test indicated a synergistic effect with respect tosuppression of migration and invasion.Conclusion: Co-expression plasmid pGS could prevent the proliferation andmigration,promote apoptosis,compared to pSi-Stat3or pGRIM-19. The mechanism ofsuppression may be that siRNA-Stat3inhibited Stat3gene expression, and then Stat3proteinwas reduced; In addition, GRIM-19of high expression directly interacts withSTAT3,inhibiting its gene stimulatory function.In brief,a combined-gene therapy withco-expression of SiRNA-Stat3and GRIM-19showed a synergistic effect with respect tosuppression of tumors in vitro.