A role for L-α-lysophosphatidylinositol and GPR55 in the modulation of migration, orientation and polarisation of human breast cancer cells

Ruth Ross1, Lesley Ford1, Anke Roelofs1, Sharon Anavi-Goffer1, Michael Rogers1, Andrew Irving2, Ann Rajnicek1. 1University of Aberdeen, Aberdeen, United Kingdom, 2University of Dundee, Dundee, United Kingdom.

Increased circulating levels of lysophospholipid, L-α-lysophosphatidylinositol (LPI) have been found in patients with cancer. LPI has recently been demonstrated to activate the orphan receptor, GPR55. The aim of this study was to investigate the effect of LPI and GPR55 in breast tumour cell migration, orientation and polarisation.

Quantitative PCR analysis revealed that GPR55 was expressed in the highly metastatic MDA-MB-231 cell line, while the low-metastatic MCF7 cell line expressed much lower levels. LPI produced a concentration-related stimulation of [35S]GTPγS binding in membranes from MDA-MB-231 cells, with Emax and pEC50 values of 51 ± 11 % and 6.47 ± 0.45 respectively. In a Boyden chamber transwell chemotaxis assay, pre-incubation of MDA-MB-231 cells with LPI (1 μM) significantly enhanced FBS-induced migration to 131 ± 28 % of vehicle control. Vector-transfected MCF7 cells did not migrate towards FBS and were unaffected by LPI. However, MCF7 cells over-expressing recombinant GPR55 migrated towards FBS. Furthermore, LPI enhanced FBS-induced migration in these cells, in a similar manner to that observed in MDA-MB-231 cells. LPI-mediated enhancement of migration of GPR55 transfected MCF7 cells was completely prevented by co-transfection with siRNA to GPR55. Nanometric grooved surfaces have previously been used to demonstrate that the surface topography influences the ability of cells to elongate (polarize) along the grooves. MDA-MB-231 cells incubated with 0.01% DMSO on nanogrooved slides of 4μm wide, 520 nm depth significantly elongated (polarized) in comparison to cells on flat surfaces. This effect was further enhanced in the presence of LPI (1μM), which caused a robust elongation, both on the grooved and flat surface.

Our findings suggest that effects on the actin cytoskeleton may contribute to the documented pro-tumoral effects of LPI and that GPR55 may play an important role in the modulation of the metastasis of breast tumour cells.