B297: Apical SLC9A3R1 links high-grade colorectal cancer morphology to genomic instability
1Centre for Cancer Research and Cell Biology, Queen’s University Belfast, Belfast, UK,2Department of Histopathology, Royal Victoria Hospital, Belfast, UK
High-grade colorectal cancer (CRC) morphology predicts poor clinical outcome but prognostic mechanisms remain unclear. The multifunctional adaptor protein SLC9A3R1 links Ezrin/Radixin/Moesin (ERM) actin-binding proteins to the plasma membrane while SLC9A3R1 membrane recruitment is enhanced by the tumour suppressor PTEN. We have previously shown that apical SLC9A3R1 intensity governs CRC gland morphology in a three-dimensional (3D) organotypic culture model and inversely associates with histological grade in human CRC. Aggressive, high-grade CRCs manifest mitotic defects and genomic instability. We hypothesize that apical SLC9A3R1 intensity provides a mechanistic link between CRC morphology and mitotic integrity.
We used PTEN-expressing and -deficient 3D organotypic Caco-2 cultures as models of CRC gland formation with high or low apical SLC9A3R1 respectively. We assessed mitotic spindle integrity by ?-tubulin, pericentrin and Aurora Kinase (AK) immunofluorescence in 3D cultures. In 35 human CRCs, apical SLC9A3R1 intensity was assessed by semi-quantitative immunohistochemistry and spindle integrity by quantitative AK immunofluorescence. Spindle architecture during mitosis was categorized as normal bipolar or abnormal multipolar, that invokes instability, aneuploidy and tumourigenesis.
High apical SLC9A3R1 intensity in parental, PTEN-expressing 3D cultures associated with normal bipolar mitosis. Conversely, low apical SLC9A3R1 intensity in the PTEN-deficient subclone invoked multipolar mitosis, in up to 18% glandular structures. Upregulation of apical SLC9A3R1 rescued gland morphology and restored bipolar mitosis in PTEN-deficient 3D cultures. In human CRCs, apical SLC9A3R1 intensity inversely associated with multipolar mitosis (r=-0.43; p=0.012) as well as high-grade CRC morphology (frequency of multipolar mitoses 10.8±1.7, 20.7±2.2 and 23.0±1.9 in grade 1, 2 and 3 CRCs respectively; p=0.001).
This study shows that apical SLC9A3R1 intensity provides a novel, drug-targetable mechanistic link between CRC morphology and multipolar mitosis, implicated in chromosome mis-segregation, instability and neoplastic progression.