Functional expression of calcium-permeable canonical transient receptor potential 4-containing channels promotes...

The proton sensing ovarian cancer G protein coupled receptor 1 (OGR1, aka GPR68) promotes expression of the canonical transient receptor potential channel subunit TRPC4 in normal and transformed cerebellar granule precursor (DAOY) cells. OGR1 and TRPC4 are prominently expressed in healthy cerebellar tissue throughout postnatal development and in primary cerebellar medulloblastoma tissues. Activation of TRPC4-containing channels in DAOY cells, but not non-transformed granule precursor cells, results in prominent increases in [Ca²⁺ ]_i and promotes cell motility in wound healing and transwell migration assays. Medulloblastoma cells not arising from granule precursor cells show neither prominent rises in [Ca²⁺ ]_i nor enhanced motility in response to TRPC4 activation unless they overexpressTRPC4. Our results suggest that OGR1 enhances expression of TRPC4-containing channels that contribute to enhanced invasion and metastasis of granule precursor-derived human medulloblastoma.

Aberrant intracellular Ca²⁺ signalling contributes to the formation and progression of a range of distinct pathologies including cancers. Rises in intracellular Ca²⁺ concentration occur in response to Ca²⁺ influx through plasma membrane channels and Ca²⁺ release from intracellular Ca²⁺ stores, which can be mobilized in response to activation of cell surface receptors. Ovarian cancer G protein coupled receptor 1 (OGR1, aka GPR68) is a proton-sensing G_q -coupled receptor that is most highly expressed in cerebellum. Medulloblastoma (MB) is the most common paediatric brain tumour that arises from cerebellar precursor cells. We found that nine distinct human MB samples all expressed OGR1. In both normal granule cells and the transformed human cerebellar granule cell line DAOY, OGR1 promoted expression of the proton-potentiated member of the canonical transient receptor potential (TRPC) channel family, TRPC4. Consistent with a role for TRPC4 in MB, we found that all MB samples also expressed TRPC4. In DAOY cells, activation of TRPC4-containing channels resulted in large Ca²⁺ influx and enhanced migration, while in normal cerebellar granule (precursor) cells and MB cells not derived from granule precursors, only small levels of Ca²⁺ influx and no enhanced migration were observed. Our results suggest that OGR1-dependent increases in TRPC4 expression may favour formation of highly Ca²⁺ -permeable TRPC4-containing channels that promote transformed granule cell migration. Increased motility of cancer cells is a prerequisite for cancer invasion and metastasis, and our findings may point towards a key role for TRPC4 in progression of certain types of MB.