Background and purpose:  Increased circulating levels of L‐α‐lysophosphatidylinositol (LPI) are associated with cancer and LPI is a potent, ligand for the G‐protein‐coupled receptor GPR55. Here we have assessed the modulation of breast cancer cell migration, orientation and polarization by LPI and GPR55.

Experimental approach:  Quantitative RT‐PCR was used to measure GPR55 expression in breast cancer cell lines. Cell migration and invasion were measured using a Boyden chamber chemotaxis assay and Cultrex^® invasion assay, respectively. Cell polarization and orientation in response to the microenvironment were measured using slides containing nanometric grooves.

Key results:  GPR55 expression was detected in the highly metastatic MDA‐MB‐231 breast cancer cell line. In these cells, LPI stimulated binding of [³⁵S]GTPγS to cell membranes (pEC₅₀ 6.47 ± 0.45) and significantly enhanced cell chemotaxis towards serum. MCF‐7 cells expressed low levels of GPR55 and did not migrate or invade towards serum factors. When GPR55 was over‐expressed in MCF‐7 cells, serum induced a robust migratory and invasive response, which was further enhanced by LPI and prevented by siRNA to GPR55. The physical microenvironment has been identified as a key factor in determining breast tumour cell metastatic fate. LPI endowed MDA‐MB‐231 cells with the capacity to detect shallow (40 nm deep) grooved slides and induced marked cancer cell polarization on both flat and grooved surfaces.

Conclusions and implications:  LPI and GPR55 play a role in the modulation of migration, orientation and polarization of breast cancer cells in response to the tumour microenvironment.

This article is part of a themed issue on Cannabinoids. To view the editorial for this themed issue visit http://dx.doi.org/10.1111/j.1476‐5381.2010.00831.x