Lack of hippocalcin causes impairment in Ras/extracellular signal-regulated kinase cascade via a Raf-mediated activation process.
Hippocalcin (Hpca) is a member of the neuronal calcium sensor protein family and is highly expressed in hippocampal neurons. Hpca-deficient (Hpca(-/-)) mice display a defect in cAMP response element-binding protein (CREB) activation associated with impaired spatial and associative memory. Here we examine the involvement of Hpca in the extracellular signal-regulated kinase (ERK) cascade leading to CREB activation, because application of PD98059, a broad ERK cascade inhibitor, has resulted in similar levels of CREB activation in Hpca(-/-) hippocampus. N-methyl-D-aspartate (NMDA)- and KCl-induced phosphorylation of ERK was significantly attenuated in Hpca(-/-) hippocampal slices, as was ionomycin-induced phosphorylation of ERK, whereas forskolin and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) stimulation yielded indistinguishable levels of ERK phosphorylation in both wild-type and Hpca(-/-) slices. In an in vitro reconstitution assay system, recombinant Hpca affected neither Raf-1 protein kinase activity with recombinant MEK-1 as a substrate nor MEK-1 kinase activity with ERK2 as a substrate. Activation of Ras by NMDA and KCl stimulation of hippocampal slices showed no obvious changes between the two genotypes; however, phosphorylation of Raf-1 was significantly lower in Hpca(-/-) slices. These results suggest that Hpca plays an important role in the activation of Raf conducted by Ras.
Noguchi
Hajime
H
Department of Physiology, Toho University School of Medicine, Ohta-ku, Tokyo, Japan.
Kobayashi
Masaaki
M
Miwa
Naofumi
N
Takamatsu
Ken
K
D000818:Animals; D000831:Animals, Newborn; D002614:Chelating Agents / Q000494:pharmacology; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D051597:Hippocalcin / Q000172:deficiency*; D006624:Hippocampus / Q000187:drug effects / Q000201:enzymology; D047468:Immunoprecipitation / Q000379:methods; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D016202:N-Methylaspartate / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011189:Potassium Chloride / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology*; D013997:Time Factors; D048490:raf Kinases / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D051597:Hippocalcin; D016202:N-Methylaspartate; D011189:Potassium Chloride; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D018631:ras Proteins