TRPC1 in the regulation of pathways involved in breast cancer metastasis

Introduction: Transient receptor potential (TRP) ion channels are non-selective cation channels with diverse roles as versatile sensors to environmental cues. TRPV1 and TRPM8 are heat and cold responsive channels respectively, TRPM2 is an oxidative stress sensitive channel, and TRPC5 is important in neuronal development and is also associated with the acquisition of multidrug resistance in breast cancer cells. Although TRPC1 was the first TRP ion channel identified in mammals, its physiological function as a channel remains mysterious. The TRPC1 knockout animal has been described as having not “dramatic” phenotypes1. TRPC1 has been also described as a store-operated Ca²⁺ entry (SOCE) channel often in association with Orai and STIM proteins.

Aims: To assess the role of TRPC1 in hypoxia-mediated cellular events in PTEN-deficient breast cancer cells.

Methods: Cytosolic free Ca²⁺ ([Ca²⁺]CYT) levels were assessed using a Fluorescent Imaging Plate Reader (FLIPR). Quantitative real-time RT-PCR and immunoblotting were used to evaluate changes in mRNA and protein levels respectively. SiRNA- mediated silencing was used to block channel expression. Gene ontology analysis was performed to define genes and pathways associated with TRPC1 expression.

Results: This study identified TRPC1 as an integral player in the regulation of hypoxia-mediated events including specific regulation of the induction of specific epithelial to mesenchymal transition (EMT) markers, and activation of EGFR and STAT3 signalling. TRPC1 was also identified as a regulator of basal (constitutive) levels of HIF1α via an Akt-dependent pathway. Gene ontology analysis revealed a close association between TRPC1 and genes associated with EMT and metastasis in breast tumours. These studies represent TRPC1 as a potential therapeutic target for the control of breast cancer metastasis.