Adhesion-related kinase repression of gonadotropin-releasing hormone gene expression requires Rac activation of the extracellular signal-regulated kinase pathway.
Recent studies suggest that adhesion-related kinase (Ark) plays a role in gonadotropin-releasing hormone (GnRH) neuronal physiology. Ark promotes migration of GnRH neurons via Rac GTPase and concomitantly suppresses GnRH gene expression via homeodomain and myocyte enhancer factor-2 (MEF2) transcription factors. Here, we investigated the signaling cascade required for Ark inhibition of the GnRH promoter in GT1-7 GnRH neuronal cells. Ark repression was blocked by the MEK/ERK pathway inhibitor, PD98059, and dominant negative MEK1 but was unaffected by dominant negative Ras. Inhibitors of the Rho family GTPases, Clostridium difficile toxin B (Rho/Rac/Cdc42 inhibitor) and Clostridium sordellii lethal toxin (Rac/Cdc42 inhibitor), blocked Ark inhibition of GnRH transcription. Moreover, dominant negative Rac blunted both Ark activation of ERK and repression of the GnRH promoter, demonstrating an essential role for Rac in coupling Ark to ERK activation. Like Ark, a constitutively active mutant of Rac suppressed GnRH transcription in an ERK-dependent manner. Finally, Ark-mediated repression was significantly attenuated by a dominant negative MEF2C, whereas repression induced by constitutively active Rac was unaffected, indicating that MEF2 proteins are not targets of the Ark --> Rac --> MEK --> ERK cascade. The data suggest that Ark suppresses GnRH gene expression via the coordinated activation of a Rac --> ERK signaling pathway and a distinct MEF2- dependent mechanism.
Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
Melissa P
MP
Allen
Mei
M
Xu
Daniel A
DA
Linseman
John E
JE
Pawlowski
Gary M
GM
Bokoch
Kim A
KA
Heidenreich
Margaret E
ME
Wierman
D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000378:metabolism; D005419:Flavonoids / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics* / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000502:physiology; D015513:Oncogene Proteins; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020703:ras GTPase-Activating Proteins / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D000094963:Axl Receptor Tyrosine Kinase
D004791:Enzyme Inhibitors; D005419:Flavonoids; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D020703:ras GTPase-Activating Proteins; D007987:Gonadotropin-Releasing Hormone; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000094963:Axl Receptor Tyrosine Kinase