Predictive and prognostic value of GIRK in breast cancer

Recent findings suggest that G-Protein activated K+ channels (GIRKs) are present in cancer cells and may contribute to the malignancy of breast tumours. Although a positive correlation of GIRK expression with disease progression was found in preliminary studies, a detailed insight on the clinical role of GIRK proteins in promotion, progression and on their potential use as therapeutic or prognostic target, does, at present, not exist. This proposal aims to investigate the impact of GIRK expression on clinical parameters during the course of breast cancer in a study cohort of 1281 patients. The subtype(s) of breast cancer where GIRK overexpression occurs will be identified in a screening.cohort (n=200). A possible correlation the GIRK overexpression with the course of the disease, with different treatment paradigms and with survival rates will be investigated in a validation cohort (n=1081). Several isoforms and splice variants of GIRK protein that are known to occur in breast cancer cells will be differentially analysed in the prevailing retrospective study. The following specific goals will be pursued: Expression levels of GIRK1, splice variants thereof and of GIRK4 will be analysed in primary tumours, lymph nodes and remote metastases of four different breast cancer cohorts (as classified by ER, PR and Her2neu status). GIRK expression patterns will be correlated with histological subtype, axillary lymph node involvement, with disease free survival and overall survival. GIRK expression will be correlated with the response to treatment. GIRK expression patterns will be correlated with the metastatic potential of a given tumour of the breast. We believe that the results may well sustain our efforts to fight cancer, by identifying novel and useful prognostic and predictive factors on which the decisions on treatment paradigms can be based. In addition the outcome of the proposal could lead to the identification of a novel pathophysiological signal transduction cascade that may be used as a therapeutic target towards a more efficient and improved treatment of this deleterious disease, but also of other malignancies.

Breast cancer is the most common cancer among women worldwide. Five thousand five hundred women are diagnosed with breast cancer and approximately 1500 women die of this disease each year despite access to screening programs for early detection, and to modern diagnostic methods as well as state of the art treatment options in Austria. In order to improve patient care and to select the right treatment for each individual patient, it is required to investigate the potential use of other molecules as prognostic or predictive biomarkers for breast cancer. G-protein coupled inward rectifier potassium channels (GIRKs) are downstream effectors of many GPCRs and are involved in the regulation of the electrical transmembrane potential by influencing potassium flow through the plasma membrane. Thereby, they contribute to the regulation of cellular excitability and physiological roles include functions such as the rhythmic control of the heartbeat. Four GIRK subunits (GIRK1-4) exist in humans and they form ion channels within the plasma membrane. We focused on GIRK1 encoded by the KCNJ3 gene and its use as prognostic and/or predictive marker in breast cancer due to recent reports that GIRK1 expression in the primary tumor might be linked to increased metastatic potential and worse clinical outcome in small series of patients with early breast cancer. In this project we could establish, on the one hand, a new methodology to reliably detect GIRK1 by immunohistochemistry and by in-situ hybridization technique (detection of messenger ribonucleic acid with fluorescent dyes) which is now available for the first time not only in cancer research but also for further studies of the biologic role of GIRK1 in physiology, cardiology, neurology or endocrinology. On the other hand, we demonstrated that GRIK1 is (a) overexpressed in breast cancer tissue compared to normal mammary epithelium, (b) is linked to ER positive breast cancer only, and (c) correlated to a significantly worse disease free survival and overall survival in patients with operated ER-positive early breast cancer. In multivariable analysis we could establish GIRK1 expression as an independent prognostic biomarker in early breast cancer. In the future GIRK1 expression may be used as a biomarker to select women with ER- positive early breast cancer having a higher risk for relapse and metastasis as an inclusion criterion of prospective studies to improve outcome with new treatment strategies.