Exposure to Hypoxic Conditions Up-regulates HER2 in Breast Cancer Cell Lines

Tissue specimen quality is becoming increasingly important for basic research and routine clinical results. Warm ischemia time (WIT) affects human epidermal growth factor receptor 2 (HER2) immunohistochemistry (IHC) scores. However, the role of WIT on HER2 modulation remains unclear. We hypothesized that the WIT-mediated increase in HER2 IHC scores was caused by hypoxia. Therefore, this study aimed to determine the mechanism by which WIT mediates the increase in HER2.

HER2 mRNA expression was measured in 4T1, SKBR3, and HCC1954 breast cancer cell lines using real-time PCR following hypoxia exposure. The membrane proteins were isolated and extracted using the Mem-PER™ Plus Membrane Protein Extraction Kit (Thermo Fisher Scientific, Waltham, MA, USA) or evaluated through non-permeabilized immunofluorescent analysis.

Hypoxic conditions up-regulated GLUT1 mRNA expression but not HER2 expression. The HER2 membrane protein fraction increased in response to hypoxic conditions. Nonpermeabilized immunofluorescence analysis showed that membrane-bound HER2 was also promoted under hypoxic conditions.

HER2 is not regulated at the mRNA level; however, the level of membrane-bound HER2 increases in response to hypoxia.