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Title: Activation of mitogen-activated protein (MAP) kinase by the luteinising hormone-releasing hormone (LHRH) receptor
Author: Sim, Pauline J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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The ability of the luteinising hormone-releasing hormone (LHRH) receptor to activate multiple signal transduction pathways (additional to its conventional activation of phospholipase C, PLC) was investigated. In particular the potential activation of the mitogen-activated protein (MAP) kinases was explored using an in vitro kinase activity assay, establishing that LHRH induces a marked and sustained increase in MAP kinase activity. Experiments with the Ca2+ ionophore, ionomycin and the phorbol ester, phorbol 12, 13-dibutyrate (PDBu) were performed to assess whether the consequences of phosphoinositide hydrolysis evoked by the LHRH receptor such as Ca2+ mobilisation or PCK activation could mimic the LHRH-induced activation. This effect could be partially mimicked by PDBu, but not by ionomycin. The role of PKC in LHRH-induced MAP kinase activation was further examined. The PKC inhibitors GF109203X, rRo-31 8220 and H7 or the downregulation of phorbol ester-sensitive PKC isoforms prevented the LHRH- and PDBu-induced responses. The LHRH- induced response was relatively resistant to H7, consistent with the possibility that the LHRH receptor may differentially activate one or more PKC species in gonadotrophs. The LHRH-induced response was additionally prevented by the tyrosine kinase inhibitors genistein and MDC or was partially mimicked by the tyrosine phosphatase inhibitor pervanadate. In order to confirm these results with an independent technique, the phosphorylation-induced gel mobility shift in immunoreactive p42 and p44 MAP kinases was determined. Both p42 and (to a lesser extent) p44 species displayed a reduced electrophoretic mobility after a 10-60 min stimulation with LHRH in a concentration-dependent manner. Pertussis toxin (PTx) also prevented the majority of the LHRH-induced MAP kinase activation (or gel mobility shift), providing the first indication of Gαi/o -mediated signal transduction by the LHRH-receptor. Mastoparan (which activates Gαi/o proteins) partially mimicked the effect of LHRH in a manner which was also sensitive to PTx.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available