Pregnancy Hormone Mediated Tumorigenesis in BRCA1 Defective Breast Cancers

Abstract

Background and ObjectiveBRCA1 mutations predispose to breast and ovarian cancers, the exact reason for the tissue specificity is unknown. The role of hormonal factors estrogen/estrogen receptor α (ER‐α) was hypothesized to be a major contributing factor for this tissue specificity. However, tumor progression in BRCA1 defective condition could not be controlled by inhibiting ER‐α as they either lack or exhibit very low expression of ER‐α, progesterone receptor, and human epidermal growth factor receptor. In addition to these hormone receptors, the prominent hormone known to be important for the development and differentiation of breast tissue is the Human Chorionic Gonadotropin (hCG). Thus, we speculated the role of hCG, especially the β‐hCG, to be the key molecule actively contributing to the tumorigenesis in TNBCs.In our previous study, we have identified for the first time that β‐hCG expression is linked to BRCA1 status. β‐hCG overexpression was observed in BRCA1 mutated breast cancer cells and conditional knockout mouse models. ChIP and luciferase assay also demonstrated the transcriptional regulation of BRCA1 over β‐hCG. β‐hCG mediate signaling through TGFβRII and promotes migration and invasion predominantly in BRCA1 mutated breast cancer cells (Sengodan et al., 2017). In accordance with the above findings, the present study aims to analyze the effectiveness of β‐hCG as a potential diagnostic marker for BRCA1 mutated cancers. This involves the analysis of β‐hCG expression in cancer tissues, followed by a detailed investigation of its link with BRCA1 mutation and analysis of its protein level in the serum of BRCA1 defective cancer patients also, to understand the mechanism of transcriptional regulation of BRCA1 over β‐hCG.MethodsImmunohistochemical analysis, ELISA, Cloning, Protein expression and purification, Electrophoretic Mobility shift Assay (EMSA)ResultsImmunohistochemical analysis of β‐hCG in tumor tissue microarray showed a strong positive expression of β‐hCG in BRCA1mutated breast cancer. Significant levels of β‐hCG in serum was not observed in breast cancer patients when compared to age matched normal control group probably because detectable levels of β‐hCG may not be present in blood. This analysis has to be carried out in a larger cohort of patient samples. To understand the transcriptional regulation of BRCA1 over β‐hCG, the DNA binding domains of BRCA1were cloned into pET‐28b vector, expressed in BL21DE3 cells and purified by Ni‐NTA affinity chromatography. Purified proteins were used for electrophoretic mobility shift assay (EMSA). Results of EMSA showed that BRCA1 did not exhibit any specific binding with β‐hCG promoter. These results suggest that BRCA1 regulation could be due to protein‐protein association with additional DNA binding transcription factors which has to be elucidated in future experiments.ConclusionThe present study highlights the significance of the regulation of β‐hCG in BRCA1 mutated cancers, since a very high expression of β‐hCG in BRCA1 mutated breast cancer is observed, further a detailed study on the same will provide more insights into the exact role of this molecule during breast cancer progression.