Spatial and temporal regulations of MAPKinases ERK1/2 in the somatolactotroph cell line GH4C1
Caroline Zeiller1, Marie-Pierre Blanchard2, Morgane Pertuit1, Sylvie Thirion1, Alain Enjalbert1, Anne Barlier1 & Corinne Gerard1
Somatotroph adenomas are characterized by growth hormone hypersecretion and cell proliferation. We have previously identified crosstalk between the cAMP pathway and the MAPKinases ERK1/2 cascade and shown the central place of the MAPKinases in the control of the pituitary function in GH4C1 somatolactotroph cell line.
The spatio-temporal organization of the signalling partners governs signalling fidelity and encodes the specificity of biological responses. Our aims consisted in dynamic imaging of living GH4C1 cells to explore spatiotemporal dynamic partners involved in the cross-talk between cAMP pathway and the ERK1/2 cascade in GH4C1. Time course, intensity and subcellular localisation of ERK1/2 activation are assessed by FRET imaging of genetically encoded biochemical sensors (EKAR located in nucleus or in cytoplasm, Harvey et al. 2008).
Our first results show that the activation of ERK1/2 biochemical sensors is responsive in cytoplasm and in nucleus to cAMP-coupled neuropeptides. We are investigating the kinetics of this activation in both compartments and their potential alterations induced by overexpression of dominant negative mutants of Ras and Rap1. Indeed, although Ras and Rap1 GTPases are recruited for the activation of ERK1/2, they are involved in opposite effect on hormonal secretion by cAMP coupled neuropeptide. These results showed that physiological response of somatotroph cells is maintained by precise spatio-temporal organization of ERK1/2.