title: Control of microtubule assembly-disassembly by calcium-dependent regulator protein.
abstract: The Ca2+-dependent regulator (CDR) protein of cyclic nucleotide phosphodiesterase is a low molecular weight, acidic, Ca2+-binding protein which has been implicated in a number of Ca2+-dependent enzymatic functions. Indirect immunofluorescence has revealed that CDR is specifically associated with the chromosome-to-pole region of the mitotic apparatus during metaphase-anaphase in a pattern distinctly different from that of similar cultured cells stained with antitubulin. This characteristic localization in the mitotic half-spindle suggested a role for CDR in the control of microtubule assembly-disassembly during mitosis. Thus, CDR was examined for its effects on microtubule polymerization in vitro. It was determined that stoichiometric concentrations of CDR and a homologous Ca2+-binding protein, skeletal muscle troponin C, both inhibited and reversed microtubule assembly in a Ca2+-dependent manner. CDR-dependent inhibition of in vitro microtubule assembly occurred at physiological Ca2+ concentrations (approximately 10 micron) that, in the absence of CDR, caused only a slight reduction in polymerization. At Ca2+ concentrations in the low physiological range (less than 1 micron), no inhibition was observed. These biochemical results, together with the immunofluorescent localization of CDR in the mitotic half-spindle, provide evidence that Ca2+ is an endogenous regulator of microtubule disassembly through the activity of CDR.
mesh_terms: D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology*; D002352:Carrier Proteins / Q000494:pharmacology*; D066298:In Vitro Techniques; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D010320:Parvalbumins / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D051381:Rats; D014336:Troponin / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D002352:Carrier Proteins; D010320:Parvalbumins; D014336:Troponin; D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases; D010727:Phosphoric Diester Hydrolases; D002118:Calcium