UCH-L1 involved in regulating the degradation of EGFR and promoting malignant properties in drug-resistant breast cancer.

Ubiquitin carboxy terminal hydrolase-L1 (UCHL1) belongs to the UCH proteases family that deubiquitinates ubiquitin-protein conjugates in the ubiquitin-proteasome system. Our previous research showed that UCH-L1 and EGFR could regulate the expression of P-gp, CD147 and MMPs in multi-drug resistance (MDR) breast cancer cells, respectively. But it is still unclear whether direct regulation exists between the UCH-L1 and EGFR in MDR breast cancer. In order to clarify this, MDR human breast carcinoma cell line MCF7/Adr, that expresses relatively high UCH-L1, and its parental cell line MCF7, that expresses relatively low UCH-L1, were chosen for this study. We added ubiquitin proteasome inhibitor MG-132 into the culture of MCF7/Adr cells and transfected pIRES2-UCH-L1-EGFP plasmid into MCF7 cells, respectively. Using quantitative real-time polymerase chain reaction and western blot analyses, we found accompanying over-expression of UCH-L1, EGFR was up-regulated in both MCF7/ADR and MCF7 cells. Preliminary results indicated the degradation of EGFR might be regulated by ubiquitin level. So we speculated that up-regulated UCH-L1 could promote expression level of EGFR, thereby enhance the invasion and metastasis abilities of tumor cells. Moreover, to further explore the role of UCH-L1 and EGFR, we investigated the expression of UCH-L1, EGFR and P-gp in 65 local advanced breast cancer cases by immunohistochemistry assay. The result showed that the patients not responding to chemotherapy had higher UCH-L1, EGFR and P-gp expression levels and more lymph nodes metastasis. The Kaplan-Meier survival analysis showed that the patients with elevated UCH-L1 expression after chemotherapy presented shorter overall survival and disease free survival times than those with down-regulated or unchanged expression of UCH-L1. Our findings suggest that UCH-L1 may be an indicator of chemotherapy-response and poor-survival in breast cancer. UCH-L1 might be an appropriate target for improving chemo-resistant breast cancer therapy.