By screening a fetal liver cDNA library at reduced stringency for v-raf-related sequences, Mark et al. (1986) found a
sequence in addition to the expected RAF1 . This sequence, which they called PKS (presumably for 'protein
kinase sequence'), showed 71% nucleotide homology to RAF1.
General function
Comment
Cellular localization
Comment
Ovarian function
Luteolysis
Comment
Chen DB, et al reported that prostaglandin F2alpha stimulates the
Raf/MEK1/mitogen-activated protein kinase signaling cascade in
bovine luteal cells.
Three isoforms of the Raf family of oncoprotein kinases (A-Raf, B-Raf, and Raf-1
or c-Raf) were detected in bovine luteal cells. Raf-1 and B-Raf, but not A-Raf,
were activated by PGF2alpha (1 microM) and the pharmacological PKC activator
phorbol myristate acetate (PMA, 20 nM). Kinetic analysis revealed that
PGF2alpha rapidly and transiently activated Raf-1.
In vitro protein kinase assays
demonstrated that activation of Raf-1 and B-Raf resulted in the phosphorylation
and activation of MAPK kinase (MEK1), which subsequently phosphorylated p42mapk. As determined by hyperphosphorylation, tyrosine phosphorylation, and
enzymatic activity, p42mapk and p44mapk were rapidly and transiently activated
by both PGF2alpha (1 microM) and PMA (20 nM). Additionally, both PGF2alpha
(1 microM) and PMA (20 nM) stimulated phosphorylation of Raf-1, MEK1, and
p42mapk in 32P-labeled cells. The data demonstrate that PGF2alpha activates the
Raf/MEK1/p42/44mapk signaling cascade in bovine luteal cells and that the
actions of PGF2alpha are mimicked by the PKC activator PMA. Activation of the
Raf/MEK1/MAPK signaling cascade by PGF2alpha in luteal cells provides a
mechanism to transduce signals initiated by PGF2alpha receptors on the cell
surface into the nucleus.
Expression regulated by
Eicosanoids
Comment
Ovarian localization
Granulosa, Luteal cells
Comment
Adenosine 5'-Triphosphate Activates Nuclear Translocation of Mitogen-Activated Protein Kinases Leading to the Induction of Early Growth Response 1 and Raf Expression in Human Granulosa-Luteal Cells.
Tai CJ, et al .
With the stimulation of many types of cell surface receptors, MAPKs are activated. We have previously demonstrated an effect of extracellular ATP on ERKs and gonadotropin- induced progesterone secretion, implicating the significance of ATP in the regulation of ovarian function. However, little is known about the specific role of ATP in the subsequent MAPK-induced signaling cascade in human granulosa-luteal cells (hGLCs). The present study was designed to examine the effect of ATP on the activation of the MAPK signaling pathway, including nuclear translocation and the expression of the immediate early genes in hGLCs. Western blot analysis, using a monoclonal antibody, which detected the total and phosphorylated forms of ERK1 and ERK2 (p42(mapk) and p44 (mapk), respectively), demonstrated that exogenous ATP evoked ERKs in a dose- and time-dependent manner. In contrast, p38 and JNK were not significantly activated after ATP treatment. To examine the translocation of activated ERKs, fluorescein isothiocyanate-conjugated secondary antibody was used to detect the distribution of total and phosphorylated ERKs. Immunofluorescent staining revealed that phosphorylated ERKs were translocated from cytoplasm into nucleus subsequent to 10 弮m ATP treatment. To study the gene(s) induced by exogenous ATP, mRNA was extracted from hGLCs in the presence or absence of 10 弮m ATP. Gene array for 23 genes associated with members of the mitogenic pathway cascade and immediate early genes revealed that the expression of early growth response 1 and c-raf-1 was increased. To our knowledge, this is the first demonstration of the ATP-induced nuclear translocation of MAPKs in the human ovary. These results suggest that the MAPK signaling pathway plays a role in mediating ATP actions in the human ovary.