The role of prolactin receptor in ovarian cancer

Abstract

Ovarian cancer is the most lethal gynaecological malignancy affecting women. Surgery and chemotherapy are the main treatments, but the development of resistance to chemotherapy remains the main obstacle to treatment, necessitating the development of other therapeutic modalities. Prolactin (PRL) is a polypeptide hormone which has various function in vertebrates, including lactation, reproduction, mammary cell growth and differentiation and immune functions. Prolactin receptor (PRLR) and ligands are expressed in many different types of cells, and a link between prolactin and cancer has been suspected for many years. Research studies have demonstrated a role for PRL and PRLR, most importantly in breast and ovarian cancers, but also in a variety of other cancers. This study examines the effect of PRLR knockdown and antagonism on cell viability, apoptosis and responses to chemotherapy in a number of high grade serous carcinoma (HGSC) cell lines, namely SKOV3, COV362, ES-2, PEA-1, PEO-1, PEO-4 and one breast carcinoma cell line MCF-7. Using immunocytochemistry, Western blotting and RTqPCR, the expression of PRLR and its ligands was studied in the cell lines. The results confirmed that all the cell lines that were studied expressed PRLR, and at least one of the ligands at different levels. Using the PRLR antagonist G129R alone and combined with cisplatin had no effect on cell viability or apoptosis in SKOV-3, COV362, ES-2 and MCF-7. The stable knockdown of PRLR in cell lines was established in the ovarian carcinoma cell line PEO-1 and the breast carcinoma cell line MCF-7. The mRNA from cells with stable knockdown of PRLR of PEO1, and MCF-7 cells was sent for RNA sequencing in order to study the changes in gene expression on knocking down PRLR, with the aim of understanding the role of PRLR in tumour cell biology further. Several interesting pathways were affected, including early/late oestrogen response and MYC target V1 pathways. Selected genes from these pathways were explored further. My results showed that all cell lines that were used in this project expressed PRLR and its ligands, but the ligands varied from one cell line to another. G129R antagonist had no effect on cell viability or apoptotic activity in any of the cell lines when used alone and no additive response when it was used along with cisplatin in all cell lines. The RNA-seq that resulted from knocking down PRLR in MCF-7 showed three interesting pathways. Selected genes from early/late oestrogen response, including ESR1, DHRS2, TFAP2C, SLC7A5, XBP1, ADCY9, SULT2B1 and CCND1, were validated by RTqPCR in PEO-1, OVCAR-3 and MCF-7. The expression of ESR1, DHRS2, SLC7A5, ADCY9 and CCND1 was aligned with the results of RNA-seq in siRNA PRLR MCF-7, but TFAP2C, XBP-1 and SULT2B showed no significant changes. However, there was no significant change in the expression in knockdown PEO-1 and OVCAR-3, apart from ADCY9, which was significantly up-regulated in knockdown PEO-1, while SULT2B1 were significantly down-regulated. Different systems and control mechanisms may therefore be applied to study different organs as well as different mechanisms between cell types within the same organ.