Protean agonism of the lysophosphatidic acid receptor‐1 with Ki16425 reduces nerve growth factor‐induced neurite outgrowth in pheochromocytoma 12 cells

We report here a novel role for the constitutively active lysophosphatidic acid receptor‐1 (LPA 1 ) receptor in providing Gβγ subunits for use by the Trk A receptor. This enhances the ability of nerve growth factor (NGF) to promote signalling and cell response. These conclusions were based on three lines of evidence. Firstly, the LPA 1 receptor was co‐immunoprecipitated with the Trk A receptor from lysates, suggesting that these proteins form a complex. Secondly, Ki16425, a selective protean agonist of the LPA 1 receptor, decreased constitutive basal and LPA‐induced LPA 1 receptor‐stimulated GTPγS binding. Ki16425 reduced the LPA‐induced activation of p42/p44 mitogen activated protein kinase (MAPK), while acting as a weak stimulator of p42/p44 MAPK on its own, properties typical of a protean agonist. Significantly, Ki16425 also reduced the NGF‐induced stimulation of p42/p44 MAPK and inhibited NGF‐stimulated neurite outgrowth. Thirdly, the over‐expression of the C‐terminal GRK‐2 peptide, which sequesters Gβγ subunits, reduced the NGF‐induced activation of p42/p44 MAPK. In contrast, the stimulation of PC12 cells with LPA leads to a predominant G i α2‐mediated Trk A‐independent activation of p42/p44 MAPK, where Gβγ subunits play a diminished role. These findings suggest a novel role for the constitutively active LPA 1 receptor in regulating NGF‐induced neuronal differentiation.