The IgLON family in ovarian cancer : functional characterisation of LSAMP and NEGR1 in comparison with the tumour suppressor OPCML

• Main Author: Christen, Sarah
• Format: Dissertation
• Language: English
• Published: Imperial College London 2013
• DOI: 10.25560/14612

Out of all gynaecological cancers, epithelial ovarian cancer (EOC), a mainly sporadically occurring disease affecting postmenopausal women, exhibits the highest fatality-to-case ratio. Further research is therefore urgently required to combat the disease. In previous studies, our group identified the IgLON protein OPCML to be an important, frequently epigenetically inactivated (>80%) tumour suppressor in EOC. On the molecular level, OPCML functions by directly interacting with and subsequently endocytotically downregulating a broad repertoire of receptor tyrosine kinases (RTKs). During this PhD project, the aim was to determine if LSAMP and NEGR1, two further IgLON family members, function in a similar manner. Bioinformatic approaches as well as in vitro experiments were used to address issues such as sequence similarity, colocalisation or interaction; furthermore, overexpression and knockdown clones were generated to determine the impact of IgLON presence/absence on cellular characteristics such as RTK expression, proliferation or migration. While LSAMP was found to potentially function in a similar manner as OPCML in the ovarian cancer cell line SKOV3 by reducing RTK expression, proliferation and colony formation, its functions in the ovarian epithelial surface cell line OSE-C2 were less clear and require further validation. For NEGR1, a striking downregulation of RTKs, including those which had been unaffected by OPCML in previous experiments – such as EGFR, HER3 or FGFR2 – was observed in transfected SKOV3 cells. Downregulation seemed to occur both via lysosomal and proteasomal pathways, and resulted in substantial reduction of cell proliferation and colony formation. Overall, these results suggest that the IgLON family could function as a broad regulator of RTK expression and function. Since IgLONs are extracellular proteins, they represent excellent subjects for drug development as no intracellular delivery or gene therapy is necessary. To our knowledge, this is the first report investigating the functional properties of LSAMP and NEGR1 in epithelial ovarian cancer.