A preformed signaling complex mediates GnRH-activated ERK phosphorylation of paxillin and FAK at focal adhesions in L beta T2 gonadotrope cells.
Most receptor tyrosine kinases and G protein-coupled receptors (GPCRs) operate via a limited number of MAPK cascades but still exert diverse functions, and therefore signal specificity remains an enigma. Also, most GPCR ligands utilize families of receptors for mediation of diverse biological actions; however, the mammalian type I GnRH receptor (GnRHR) seems to be the sole receptor mediating GnRH-induced gonadotropin synthesis and release. Signaling complexes associated with GPCRs may thus provide the means for signal specificity. Here we describe a signaling complex associated with the GnRHR, which is a unique GPCR lacking a C-terminal tail. Unlike other GPCRs, this signaling complex is preformed, and exposure of L beta T2 gonadotropes to GnRH induces its dynamic rearrangement. The signaling complex includes c-Src, protein kinase C delta, -epsilon, and -alpha, Ras, MAPK kinase 1/2, ERK1/2, tubulin, focal adhesion kinase (FAK), paxillin, vinculin, caveolin-1, kinase suppressor of Ras-1, and the GnRHR. Exposure to GnRH (5 min) causes MAPK kinase 1/2, ERK1/2, tubulin, vinculin, and the GnRHR to detach from c-Src, but they reassociate within 30 min. On the other hand, FAK, paxillin, the protein kinase Cs, and caveolin-1 stay bound to c-Src, whereas kinase suppressor of Ras-1 appears in the complex only 30 min after GnRH stimulation. GnRH was found to activate ERK1/2 in the complex in a c-Src-dependent manner, and the activated ERK1/2 subsequently phosphorylates FAK and paxillin. In parallel, caveolin-1, FAK, vinculin, and paxillin are phosphorylated on Tyr residues apparently by GnRH-activated c-Src. Receptor tyrosine kinases and GPCRs translocate ERK1/2 to the nucleus to phosphorylate and activate transcription factors. We therefore propose that the role of the multiprotein signaling complex is to sequester a cytosolic pool of activated ERK1/2 to phosphorylate FAK and paxillin at focal adhesions.
Dobkin-Bekman
Masha
M
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel-Aviv 69978, Israel.
Naidich
Michal
M
Rahamim
Liat
L
Przedecki
Fiorenza
F
Almog
Tal
T
Lim
Stefan
S
Melamed
Philippa
P
Liu
Ping
P
Wohland
Thorsten
T
Yao
Zhong
Z
Seger
Rony
R
Naor
Zvi
Z
D000595:Amino Acid Sequence; D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D022001:Focal Adhesions / Q000378:metabolism*; D005786:Gene Expression Regulation; D052681:Gonadotrophs / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D051419:Paxillin / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction; D016596:Vinculin / Q000737:chemistry; D019061:src-Family Kinases
D051419:Paxillin; D016596:Vinculin; D007987:Gonadotropin-Releasing Hormone; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases