Understanding ovarian cancer and chemoresistance through chromosome spatial organisation and nuclear motors

Abstract

20% of patients diagnosed with ovarian cancer (OC) cannot receive treatment at all due to the severity of the disease when discovered. The 80% of patients that receive treatment, as much as, 90% relapse in less than six months and, by the end of two years fail to respond to treatment as a result of multi-drug resistance. As genetic studies fail to provide a complete picture in the biology of disease, epigenetics including spatial and radial organisation of the genome has become a well established that provides a greater understanding beyond the sequence. Chromosomes are non randomly organised within interphase nuclei, which can vary slightly from cell type to cell type, their proliferation and disease status. The functional organisation within interphase nuclei is kept in place and regulated by a plethora of structural and mechanical proteins such as lamins and nuclear myosins (NMs), and along with many other proteins are known together as the nucleoskeleton. Irregularities in these proteins have been implicated in many diseases, including metastatic cancers and their chemoresistant counterparts. NM1 role in spatial chromosome organisation has been established, and with the emergence of NM6 role in nuclear organisation, both their overexpression in OC and involvement transcription presents them as an attractive co-study. This research investigates the disease-related chromosome territory (CT) positionings of OC through four key chromosomes in a panel of OC cells; SKOV-3 PEO-1 PEO-4 MDAH-2774, in addition to a control control cell line HOSEpi. Internally located CT were observed for chromosomes 1, 13 and 17 and a peripheral localisation was observed chromosome X. Chromosomes were subsequently assessed for location post-NM1/6 knockdown revealing that chromosome territories relocalised closer to the localisations of the control cell line, and following the acquisition of platinum-resistance of MDAH-2774, all four chromosomes predominated centrally in nuclei. The analysis also revealed that chromosome X might play a more fundamental role in ovarian tissue and cancer that than previously thought and the initial aim of its use as a control was challenged. Distribution discrepancies in the OC cells were found in the nuclear lamins and myosins with further investigations revealing significant elevations of NM1 and NM6. The elevations also displayed a different stoichiometry ratio in the platinum-resistant cell line PEO-4 which led to the creation of a novel lab-grade platinum-resistant cell line MDAH-2774CR from the naïve line MDAH-2774 to investigate further resistant-specific NM1/NM6 stoichiometry and spatial CT organisation in OC. Moreover, combination assays with MDAH-2774CR and NM1 knockdown resulted in cell death that surpassed its sensitive counterpart, that has future clinical potential to treat chemoresistant OC. In this research, we aim to broaden the comprehension of the many mechanisms involved in the development and progression of an aggressive cancer. The analysis of the CT positioning of 4 out of 23 chromosomes was able to reveal characteristics within OC nuclei at key milestones of the disease, making this level of investigation, and information, important in understanding OC and its successful treatment.