The investigation of mir-221-3P and pak1 gene expressions in breast cancer cell lines

The most common malignancy in women is breast cancer. Drug resistance in the treatment of cancer still remains a major clinical concern because of an insufficiency of understanding of the pathways by which cancer drugs interact with the mechanisms underlying cellular behaviour and cancerpathogenesis. Therefore, defining whether risk factor associations for breast cancer diverge by morphological and molecular features of the tumors shows an important query. Resistance to tamoxifen is seen in half of the recurrences in breast cancer. The anti-estrogen tamoxifen gains agonistic property by transactivating ERα. PAK1- mediated phosphorylation of serine 305 (S305) of ERα leads to resistance to tamoxifen. In our study, PAK1- induced suggestive tamoxifen resistance was designed. According to our hypothesis, phosphorylation of ERα-S305 by PAK1 may be reversed by PAK1 transcriptional inhibition by miR-221-3p due to miR-221-3p targeting the 3'UTR of PAK1. For this purpose, we used Real-Time PCR (qRT-PCR) to measure the expression level of miR-221-3p in ER-positive breast cancer cell lines (CRL-1500, MCF7) and breast epithelial cell line, hTERT-HME1, as control in the laboratory in our department. Increase in the expression of PAK1 depending on miR-221-3p may be related to ZR-75-1 cell line which has invasive characteristic but other two ER+ cancer cell lines, MCF7 and HCC1500, have milder cancer severity. miR-221-3p may have a role on regulation of PAK1 expression because the miR-221-3p expression level decreases while PAK1 expression level increases in SKBR3 cell line. miR-221-3p and PAK1 expression in MDA-MB-231 cell line are higher than that of hTERT-HME1 cell line may be interpreted like that miR-221-3p has no regulatory effect on of PAK1 expression in this cell line. According to these results, miR-221-3p may give crucial information about the molecular mechanism of the disease upon PAK1 activity or different mechanisms with respect to histopathology and severity of breast cancer. Key Words: miR-221-3p, PAK1, breast cancer, qRT-PCR, RT-PCR