Effect of human epidermal growth factor receptor 2 signalling on the IFN-γ pathway in luminal B breast cancer

Abstract

Previous studies showed luminal B (Human epidermal growth factor 2 +(HER2+) Estrogen receptor + (ER+) human breast carcinomas, compared to other breast cancer subtypes, are deficient in human leukocyte antigen (HLA) expression. Similarly, representative breast cancer cell line BT-474 (HER2+ER+) exhibited significantly reduced IFN-γ-inducible HLA expression, as compared to MCF-7 (HER2-ER+) and SKBR3 (HER2+ER-). Therefore, we hypothesized hyperactivation of HER2 signalling in ER+ breast cancer may interfere with interferon gamma (IFN-γ) pathway activation. To test this hypothesis, time course studies, targeted inhibition of HER2 (lapatinib or trastuzumab+pertuzumab) and ER (tamoxifen and ICI) and small interfering RNAs (siRNAs) targeting HER2 (ERBB2) and/or ER (ESR1) pathways were performed. Changes in IFN-γ pathway components, HER2, ER and HLA Class I in BT-474 and SKBR3, were assessed by flow cytometry and western blotting. Kinetic studies showed no clear inverse correlation between HER2 levels and surface HLA Class I while HER2 inhibition or knockdown resulted in reduced surface interferon gamma receptor 1 (IFNGR1) and HLA Class I. Neither phosphorylated signal transducer and activator of transcription (pSTAT-

nor interferon regulatory factor 1 (IRF-1) were significantly altered in BT-474 or SKBR3. The results suggest expression levels and/or function of IFN-γ pathway proteins may be dysregulated, likely independent of HER2 overexpression, resulting in weak IFN-γ signalling in BT-474 (HER2+ER+) and subsequent poor HLA Class I upregulation.