| Summary: | The Human Epidermal Growth Factor Receptor 2 (HER2) is an oncogene expressed in 25-30% of invasive breast cancers. The HER2 gene encodes an 185kDa transmembrane protein with tyrosine kinase activity. Gene amplification or protein expression of HER2 is a predictor of poor prognosis in women with breast cancer, and also indicates a favourable response to Trastuzumab (Herceptin) therapy, or a combinational therapy comprising Herceptin plus chemotherapy. However, resistance to Trastuzumab remains the case in approximately 50% of HER2 amplified/overexpressing tumours. Understanding the molecular mechanisms of Trastuzumab resistance is critical in the treatment of patients whose breast cancers express this aggressive disease phenotype. In this study, it is postulated that the abnormal generation of mRNA splice variants may be responsible for the continued tumour growth and progression. The aim of this study is to investigate the expression of alternative splice variants in invasive breast cancer, and to increase our understanding of the regulation of HER2 and HER2 splice variants in invasive breast cancer. The coding region of HER2 cDNA was PCR amplified in HER2 positive cell lines (SKOV-3, SKBR-3, and MDA-MB-453). The regulation of HER2 expression was investigated by siRNA silencing of the splice factor SRSF1 and its phosphorylating gene SRPK1. The role of hypoxia and the inhibition of SRPK1 via SRPIN340 were also investigated for its effects of HER2 expression in cell lines. Human cancer tissues known to be positive for HER2 were tested for the expression of alternative splice variants of HER2. RT-PCR results reveal new alternative splice variants in invasive breast cancer cells. These new alternative splice variants of HER2 have also been detected in HER2-positive breast cancer samples. Furthermore, the splice factor SRPK1 and SRSF1 have shown regulatory effects on the expression of HER2 in HER2-positive cell line MDA-MB-453. This study identifies for the first time two novel splice variants with deletions in the transmembrane and kinase domains of the HER2 gene, both with very distinct functional and structural differences. These findings conclude that alternative splicing plays a crucial role in the regulation of HER2 expression, and possibly in the response of breast cancer patients to current targeted HER2 therapies.
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