Emerging roles for multifunctional ion channel auxiliary subunits in cancer

Several superfamilies of plasma membrane channels which regulate transmembrane ion flux have also been shown to regulate a multitude of cellular processes, including proliferation and migration. Ion channels are typically multimeric complexes consisting of conducing subunits and auxiliary, non-conducing subunits. Auxiliary subunits modulate the function of conducing subunits and have putative non-conducing roles, further expanding the repertoire of cellular processes governed by ion channel complexes to processes such as transcellular adhesion and gene transcription. Given this expansive influence of ion channels on cellular behaviour it is perhaps no surprise that aberrant ion channel expression is a common occurrence in cancer. This review will focus on the conducing and non-conducing roles of the auxiliary subunits of various Ca2+, K+, Na+ and Cl- channels and the burgeoning evidence linking such auxiliary subunits to cancer. Several subunits are upregulated (e.g. Ca-v beta, Ca-v gamma) and downregulated (e.g. K-v beta) in cancer, while other subunits have been functionally implicated as oncogenes (e.g. Na-v beta(1), Ca-v alpha(2)delta(1)) and tumour suppressor genes (e.g. CLCA2, KCNE2, BK gamma(1)) based on in vivo studies. The strengthening link between ion channel auxiliary subunits and cancer has exposed these subunits as potential biomarkers and therapeutic targets. However further mechanistic understanding is required into how these subunits contribute to tumour progression before their therapeutic potential can be fully realised.