Properties of a microtubule-associated cofactor-independent protein kinase from pig brain

Abstract

A protein kinase activity was identified in pig brain that co-purified with microtubules through repeated cycles of temperature-dependent assembly and disassembly. The microtubule-associated protein kinase (MTAK) phosphorylated histone HI; this activity was not stimulated by cyclic nucleotides, Ca2" plus calmodulin, phospholipids or polyamines. MTAK did not phosphorylate synthetic peptides which are substrates for cyclic AMP-dependent protein kinase, cyclic GMP-dependent protein kinase, Ca2"/ calmodulin-dependent protein kinase II, protein kinase C or casein kinase II. MTAK activity was inhibited by trifluoperazine [IC50 (median inhibitory concn.) = 600 fLM] in a Ca2"-independent fashion. Ca2" alone was inhibitory (IC50 = 4 mM). MTAK was not inhibited by heparin, a potent inhibitor of casein kinase II, nor a synthetic peptide inhibitor of cyclic AMP-dependent protein kinase. MTAK demonstrated a broad pH maximum (7.5-8.5) and an apparent Km, for ATP of 45 /tM. Mg2" was required for enzyme activity and could not be replaced by Mn2". MTAK phosphorylated serine and threonine residues on histone HI. MTAK is a unique cofactor-independent protein kinase -that binds to microtubule structures.

Osmoregulation of Neutral Amino Acid Transport

“…The activation of system A by microtubule disruption required new protein synthesis and was not additive with the stimulation of system A by addition of serum (56). It has been suggested that a protein kinase may be associated with microtubules (57,58), and microtubule disruption may activate DNA synthesis (59) and specific gene expression (60). It is possible that a similar process may account for activation of system A by microtubule disruption in A10 cells.…”

Contraction due to microtubule disruption is associated with increased phosphorylation of myosin regulatory light chain.

“…For example, disruption of microtubules can enhance transduction of signals mediated by GTP-binding proteins (14) or activate cellular protein kinases (15). In addition, some protein kinases physically associate with microtubules (16)(17)(18). Thus, microtubule disruption might initiate biochemical signals which activate the force-generating components of the cytoskeleton.…”

Phosphorylation of type III ?-tubulin in PC 12 cell neurites during NGF-induced process outgrowth

“…Thus, the phosphorylation is elevated at least fivefold. Several microtubule-associated protein kinases derived from the brain (Scott et al, 1989;Goldenring et al, 1984), neuroblastoma (Serrano…”