Showing papers by "Javier Díaz-Nido published in 1993"

Depletion of casein kinase II by antisense oligonucleotide prevents neuritogenesis in neuroblastoma cells.

Abstract: Casein kinase II is a multifunctional protein kinase which has been implicated in the regulation of cell growth and differentiation. This enzyme is much more abundant in neurons than in any other cell type. The treatment of neuroblastoma cells with an antisense oligodeoxyribonucleotide which specifically results in the depletion of casein kinase II catalytic subunits blocks neuritogenesis. Accordingly, this enzyme may perform an essential role during neurite growth in developing neurons. Casein kinase II depletion induced by antisense oligodeoxyribonucleotide is accompanied by a site-specific dephosphorylation of microtubule-associated protein MAP1B (also referred to as MAP5, MAP1.X or MAP1.2), which is paralleled by a release of MAP1B from microtubules. We therefore propose that phosphorylation by casein kinase II may be required for the proper MAP1B functioning in the promotion of the assembly of microtubules which constitute the cytoskeletal scaffolding of growing axon-like neurites.

Heterogeneity in the phosphorylation of microtubule-associated protein MAP1B during rat brain development.

Abstract: The patterns of isoforms and of immunoreactivity of the microtubule-associated protein MAP1 B toward a panel of antibodies to phosphorylation-sensitive epitopes are different in distinct rat brain regions and change during development. This suggests the occurrence of a considerable degree of heterogeneity in the phosphorylation state of rat brain MAP1 B. It appears that MAP1 B can be phosphorylated at multiple sites that may be conventionally classified into at least two modes of phosphorylation. Mode I of phosphorylation induces significant upward shifts in the electrophoretic mobility of the protein, giving rise to “high” MAP1B isoforms, whereas the mode II of MAP1B phosphorylation does not greatly affect the electrophoretic mobility of the protein. These MAP1B phosphorylation modes are differentially regulated throughout development and show some regional specificity. Cytosolic MAP1 B is highly phosphorylated both at mode I and mode II sites in the developing rat brain, as well as in the adult olfactory bulb, where axonal growth takes place. In most adult rat brain regions, cytosolic MAP1B is highly phosphorylated at mode II sites but largely dephosphorylated at certain mode I sites. However, MAP1 B present in the particulate fraction of most rat brain region homogenates may be partially dephosphorylated at certain mode II sites, although it contains some phosphorylated mode I sites. These data are compatible with the view that different protein kinases, possibly including casein kinase II and proline-directed protein kinases, might regulate the state of phosphorylation of MAP1B in distinct localizations along the development of different neuronal populations in the brain.

High External Potassium Induces an Increase in the Phosphorylation of the Cytoskeletal Protein MAP2 in Rat Hippocampal Slices

Abstract: Depolarization induced in rat hippocampal slices by a high concentration of extracellular K+ leads to an increase in the phosphorylation of microtubule-associated protein MAP2. The comparison of the major phosphopeptides derived from in situ and in vitro phosphorylated MAP2 suggests the implication of calcium-dependent protein kinases, including calcium/calmodulin-dependent protein kinase type II and protein kinase C, in the up-phosphorylation of MAP2. In particular, a peptide containing the tubulin-binding domain of the MAP2 molecule may be phosphorylated by protein kinase C. As the association of MAP2 with the cytoskeleton may be regulated by phosphorylation, we suggest that changes in the phosphorylation level of MAP2 might be involved in synaptic remodelling in hippocampal neurons.