HER2 reduces breast cancer radiosensitivity by activating focal adhesion kinase in vitro and in vivo

Abstract

Growing evidence has demonstrated that human epidermal growth factor receptor 2 (HER2) is involved in the radiation response to breast cancer. However, the underlying mechanism remains elusive. Therefore, we investigated if HER2 overexpression is associated with radiosensitivity of breast cancer. We constructed breast cancer cell lines differing in HER2 expression by transducing HER2 cDNA or short hairpin RNA against HER2. We then assessed the radiosensitivity and investigated the potential mechanism by using cell proliferation assay, cell adhesion assays, anoikis assays, colony formation assays, and western blotting analyses. We found that HER2 introduction in breast cancer cell lines MCF-7 (low HER2 expression) and MDA-MB-231 (HER2 is not expressed) promoted cell proliferation and invasion and enhanced cell adhesion and resistance to anoikis. Moreover, HER2 reduced radiosensitivity in these two cells compared with the corresponding control. The opposite results were observed when HER2 was silenced in breast cancer cell lines ZR-7530 and SK-BR-3 (both cells with high expression of HER2) using HER2 shRNA. In addition, animal experiment results showed HER2 could enhance the radioresistance of xenograft tumors. Further studies showed HER2 promoted the phosphorylation of focal adhesion kinase (Fak) and thereby up-regulated the expression of proteins associated with the epithelial-to-mesenchymal transition such as Claudin-1, ZO-1, and ZEB-1. The inhibition of Fak activity using the Fak inhibitor (PF-562281) restored the radiosensitivity in HER2-overexpressing cells. In conclusion, HER2 reduces the radiosensitivity of breast cancer by activating Fak in vitro and in vivo. Fak might be a potential target for the radiosensitization of HER2-overexpressed breast cancer.

PI3K isoform inhibition associated with anti Bcr-Abl drugs shows in vitro increased anti-leukemic activity in Philadelphia chromosome-positive B-acute lymphoblastic leukemia cell lines

“…Lysate was purified by centrifugation for 10 min at 4°C and 20–50 μg of solubilized proteins were resolved on 10% or 12% SDS-PAGE [56]. …”

Association between breast cancer cell migration and radiosensitivity in�vitro

“…5A and B). Our previous study demonstrated that Fak-associated genes were important in HER2-mediated radio-resistance (13). Therefore, the expression of Fak was determined.…”

“…Migration assays. The migration assay was performed as previously described (13,14). Briefly, a total of 2x10 4 of MDA-MB-231 or ZR-75-30 were placed in the upper chamber of a Transwell chamber (BD Biosciences) with an 8-µm pore filter between the chambers.…”

“…E-cadherin participates in the regulation of cell adhesion, which serves a critical role in cancer cell invasion and metastasis (12). Our previous study indicated that human epidermal growth factor receptor 2 (HER2) decreased breast cancer cell radiosensitivity by activating focal adhesion kinase in vitro and in vivo (13). Therefore, cell adhesion processes, and invasion and metastatic processes may be associated with the response to radiotherapy.…”

Radiosensitivity in the breast cancer management scenario: another step forward?

“…In vitro and in vivo experiences confirmed that HER2 silenced BC cell lines had increased RSI, and that HER2 xenograft tumors had enhanced radioresistance if compared to corresponding controls. These effects on RSI seemed to be related to HER2 mediated up-regulation of phosphorylation of focal adhesion kinase (FAK); as a counterproof, RSI was restored using a FAK inhibitor (11).…”