Investigating the Role of the Planar Cell Polarity (PCP) Protein CELSR1 in Breast Cancer

Planar cell polarity (PCP) is essential for generating highly organized tissue structures and for directional cell movement/migration. The role of PCP in embryogenesis is well-documented, however its role in adult pathologies, such as cancer, is a relatively new field of research. A growing number of publications imply a significant role for PCP proteins in cancer progression and metastasis. PCP is governed by several cytosolic proteins and transmembrane receptors including the G-protein coupled receptor CELSR1. Research studies have raised the hypothesis that CELSR1 acts as a tumour suppressor in breast cancer. Our research aim was to characterise an in-vitro model to understand the molecular/cellular basis of the role of CELSR1 in breast cancer. Computational biology was used to assess CELSR1 expression in breast cancer sub-types and its impact on patient survival. Characterisation of breast cancer cell lines representing increasingly invasive breast cancer was performed through qPCR and western blot analysis to investigate CELSR1 expression and immunocytochemistry to investigate CELSR1 protein distribution. RT-PCR and Sanger sequencing were used to assess differential splicing of the C-terminus of CELSR1. Gain and loss-of-function assays were conducted to test the tumour suppressive functions of CELSR1. Bioinformatics analysis has revealed that CELSR1 expression is increased in the less invasive Luminal A subtype of breast cancer, and that higher expression of CELSR1 has positive impact on overall patient survival. In vitro studies of common breast cancer cell lines revealed that CELSR1 is more highly expressed in less invasive luminal type cell lines, but its expression is reduced in more invasive type cell lines. Furthermore, whilst less invasive breast cancer cell lines exhibit cortical enrichment of CELSR1, CELSR1 becomes localised in intracellular punctate structures adjacent to the nucleus within the highly invasive breast cancer cells. Finally, we find that overexpression of Celsr1 in highly invasive breast cancer cell lines reduces their migratory ability and proliferation. Taken together, our study is consistent with a role for CELSR1 as a tumour suppressor in breast cancer. Future studies will aim to decipher its mechanism of action.