Multifunctional Ca2+/calmodulin-dependent protein kinase is necessary for nuclear envelope breakdown

Area of Science:

• Cell Biology
• Molecular Biology
• Developmental Biology

Background:

• Nuclear envelope breakdown (NEB) is a critical event in cell division.
• Ca2+/calmodulin-dependent protein kinase (CaM kinase) is known for its roles in neuronal function.
• The specific role of CaM kinase in the cell cycle of non-neuronal cells, like sea urchin eggs, is less understood.

Purpose of the Study:

• To investigate the presence and function of multifunctional CaM kinase in sea urchin eggs.
• To determine if this enzyme is involved in the process of nuclear envelope breakdown (NEB).

Main Methods:

• Biochemical characterization of a 56-kD polypeptide in sea urchin eggs, including autophosphorylation assays.
• Comparison of the sea urchin egg polypeptide with neuronal CaM kinase using homology and antibody cross-reactivity.
• Microinjection of a synthetic peptide inhibitor (CaMK(273-302)) and a specific monoclonal antibody (mAb) into sea urchin eggs to assess their effect on NEB.

Main Results:

• A 56-kD polypeptide in sea urchin eggs was identified, exhibiting Ca2+/calmodulin-dependent autophosphorylation characteristic of multifunctional CaM kinase and showing homology to rat brain CaM kinase alpha subunit.
• A synthetic peptide corresponding to the autoinhibitory domain of neuronal CaM kinase inhibited both autophosphorylation and substrate phosphorylation in vitro, and also inhibited NEB when microinjected into eggs.
• A specific mAb recognizing neuronal CaM kinase immunoprecipitated the 56-kD sea urchin egg polypeptide and also inhibited NEB upon microinjection.

Conclusions:

• Sea urchin eggs contain a multifunctional CaM kinase homologous to its neuronal counterpart.
• This CaM kinase is implicated in the regulation of nuclear envelope breakdown during mitotic division in sea urchin eggs.