Study of miR-21 and miR-221 Expression in Breast Cancer FFPE Tissue Sections by Real Time PCR and Chromogenic in situ Hybridization

MicroRNA (miRNA) is 20 to 22nt RNA which regulates gene expression by repressing the translation of the target mRNA. It is estimated that about 30% of the expression of human genes are regulated by miRNA. Previous research has demonstrated that miRNA is highly associated with oncogenesis, cell migration and metastasis of cancer. In this study, the expression of miR-21 and miR-221 in cultured cells and clinical breast cancer (BC) FFPE samples was analyzed. Real time PCR was used to quantify the expression level of miRNA and chromogenic in situ hybridization (CISH) method was used to investigate the cellular compartments for altered miRNA expression. An increased level of miR-21 was detected in cancer cell lines MCF-7, MB-231, AGS and HeLa, and the expression of miR-221 was found to be significantly higher in BC basal subtype cell line MB-231 than luminal subtype cell line MCF-7. The increased expression of miR-21 was present in high grade, stage I and basal subtype BC samples, but was not statistically significant. There were no significant differences in miR-221 expression across BC samples from different grades, stages and subtypes. CISH results demonstrated that miR-21 and miR-221 were expressed mainly in the cytoplasm of epithelial tumor cells in BC. The expressions of miR-21 and miR-221 were undetectable in the benign tissue sections. The miR-21 and miR-221 expression was detected in almost all tumors cells in high grade BC. The high level of miR-221 expression was detected in high grades and late stages of BC. The expression of miR-21 and miR-221 is higher in infiltrating ductal carcinoma compared to infiltrating lobular carcinoma. It was also noticed that increased expressions of miR-21 and miR-221 were found in atypical hyperplasia cases.