Preliminary Reseach On ERK/MAPK Signal Transduction Mediated By GABA_B Receptor Homo-or Hetero-dimeric In HEK293 Cells

γ-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). GABAB receptors are the metabotropic GABA receptors and belong to G protein-coupled receptors family C. They are widely expressed in the presynaptic and postsynaptic of neuron. GABAB receptors have significant physiological functions such as the generation of learning and memory, synapse signal conduction. These receptors have been extremely precise regulated, they will result in nervous indiscriminate disease because of excessive activation or inhibition. The mechanism of the ERK/MAPK signal pathway mediated by GABAB receptors is not clear at present. ERK/MAPK signal pathway is an important passer which transduce the extracellular signal into the cell nucleus, it regulate processes such as cell differentiation, proliferation, immigration, apoptosis, anti- apoptosis.GABAB receptors are found in the forms of GBR1/GBR2 heterodimer, GBR1/GBR1 or GBR2/GBR2 homodimer in cells. The VFT domain of GB1 is responsible for ligand binding, while the intracellular second and third loops of GB2 take part in the combination to the Gi/o protein, followed by the activation of Gi/o protein and the mediation of downstream signal transduction.In this study, we focus on the ERK/MAPKs signal pathway induced by GABAB receptor in HEK293 cells (human embryonic kidney 293 cells). HEK293 cells were transiently co-transfected with GB1-HA and GB2-Flag, after 24 hours, the cells were incubated with GABA, the result indicated that the activation of GABAB receptor stimulate ERK1/2 activation. The activation of ERK1/2 which were mediated by GABA and CGP7930 which is the agonist of GB2 were blocked by pretreatment with the inhibitor of Gi/o protein PTX. We co-transfected GB1-HA, GB2-Flag and CD8-?ARK into cells and found that CD8-?ARK inhibited the activation of ERK1/2 which were activated by GABA and CGP7930. We transfected GB2-Flag into HEK293 cells alone and stimulated with CGP7930, the result demonstrated that CGP7930 activated ERK1/2 and PTX blocked this activation. HEK293 cells were transfected with GB1-ASA alone and treated with PTX and Baclofen which is the specific agonist of GABAB receptor. The result indicated that the activation of the GB1-ASA homodimers transiently activated EKR1/2, and this activation was sensitive to PTX.In a brief, our research demonstrated that the GABAB receptor heterodimers can activate ERK1/2 through the activation of the Gi/o protein. Moreover, theβγsubunits of Gi/o protein play an important role in this activation process. GB2 homodimers can also activate ERK1/2 and this activation was dependent on Gi/o protein. The ERK1/2 activation induced by GB1-ASA homodimers was sensitive to PTX. This research made a foundation for the further investigation in the signal pathway mechanism and function of MAPKs which mediated by GABAB receptor heterodimers and homodimers.