Assessment of TRPV4-mediated calcium influx induced by receptor activation in MDA-MB-468 breast cancer cells

Introduction: The calcium permeable ion channel TRPV4 is involved in breast cancer cell invasion, migration and metastasis and appears to be associated with poorer patient outcomes. TRPV4 transactivation by G-protein coupled receptors and receptor tyrosine kinases, have been identified as important mechanisms of regulation in other tissues and pathologies. Characterisation of these transactivation pathways present an opportunity to better understand the nature of TRPV4 signalling in breast cancer cells.

Aims: To assess the sensitivity of Ca²⁺ influx elucidated by ATP, trypsin and epidermal growth factor (EGF) to the pharmacological TRPV4 inhibitor HC067047 and the Gαq inhibitor UBO-QIC in MDA-MB-468 breast cancer cells.

Methods: MDA-MB-468 cells were plated at 6 x 103 cells per well into 384 well black plates. For the measurement of free cytosolic Ca²⁺, cells were loaded with 2 μM PBX no-wash calcium indicator dye for 60 min at 37°C, and were subsequently treated with TRPV4 and/or Gαq inhibitors for 15 min at room temperature. Intracellular Ca²⁺ levels associated with ATP, trypsin and epidermal growth factor (EGF) were then assessed using a Fluorescence Imaging Plate Reader (FLIPR).

Results: Ca²⁺ influx induced by the purinergic receptor activator ATP was unaffected by TRPV4 pharmacological inhibition. However, TRPV4 inhibition attenuated Ca²⁺ influx associated with trypsin-mediated activation of protease activated receptor 2 (PAR2) and EGF. Calcium influx induced by trypsin was UBO-QIC sensitive; in the presence of the Gαq inhibitor, TRPV4 inhibition had no effect on Ca²⁺ influx.

Discussion: These experiments suggest that PAR2 activation promotes Ca²⁺ influx in MDA-MB-468 breast cancer cells through a Gαq-dependent mechanism. Further investigation using siRNA silencing of TRPV4 and further assessment of the mechanistic components responsible for TRPV4 activation in breast cancer cells is now required.