Chromatographic Resolution and Characterization of a Nerve Growth Factor‐Dependent Kinase That Phosphorylates Microtubule‐Associated Proteins 1 and 2 in PC12 Cells

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Abstract
When the supernatant fractions from extracts of control and nerve growth factor (NGF)- or dibutyryl cyclic AMP-treated PC12D cells were applied to DEAE-Sepharose columns and proteins were eluted with a gradient of NaCl, three separate peaks of kinase activity that phosphorylated microtubule-associated proteins (MAPs) were recovered. Enhancement of the kinase activity in peak 1 was noted in the case of dibutyryl cyclic AMP-treated cells. In contrast, the kinase activity in the third peak was markedly elevated, in terms of the ability to phosphorylate MAP1 and MAP2, in the case of the extract from NGF-treated cells. This activity was designated previously as NGF-dependent MAP kinase. The apparent molecular mass of the active kinase was 45-50 kDa. The apparent Km value was 35 microM for ATP with either MAP1 or MAP2 as substrate. When the kinase activity in the fractions from the DEAE-Sepharose column was assayed in the presence of Mn2+ instead of Mg2+, another NGF-stimulated kinase activity was detected in the fractions eluted by a lower concentration of NaCl than that which eluted the Mg(2+)-activated kinase. Other growth factors, namely, epidermal growth factor and basic fibroblast growth factor, also stimulated the activity of NGF-dependent MAP kinase. Possible involvement of the kinase in the outgrowth of neurites has been suggested. The NGF-induced activation of NGF-dependent MAP kinase was blocked by the presence of K-252a. In contrast, the activation of NGF-dependent MAP kinase by basic fibroblast growth factor and by epidermal growth factor was not blocked, but actually stimulated by K-252a, a result that correlates well with the analogous actions of the drug on the outgrowth of neurites that is induced by these growth factors. The latter observation strengthens the possibility of a close relationship between the outgrowth of neurites and the activation of NGF-dependent MAP kinase.

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