Major vault protein is a substrate of endogenous protein kinases in CHO and PC12 cells

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Major vault protein (MVP) is a key component of cytosolic vault particles.
• Previous research indicated MVP phosphorylation by protein kinase C and tyrosine kinase.

Purpose of the Study:

• To investigate MVP phosphorylation by endogenous protein kinases in mammalian cell lines.
• To compare phosphorylation patterns between electric organ and mammalian MVP.
• To elucidate the role of cell-specific phosphorylation in vault function.

Main Methods:

• Cell-free phosphorylation assays using mammalian cell lines (CHO and PC12).
• Analysis of kinase activity dependence on Mg2+ and inhibition by EDTA.
• Assessment of casein kinase II involvement using inhibitors and recombinant enzyme.
• Copurification of kinase activity with vault particles.
• Investigation of vault autophosphorylation using purified vaults.

Main Results:

• Mammalian MVP (CHO, PC12) undergoes significant phosphorylation by endogenous kinases in cell-free systems.
• Phosphorylation susceptibility differs from electric organ-derived MVP.
• Phosphorylation requires Mg2+ and is sensitive to EDTA.
• Casein kinase II activity influences MVP phosphorylation, with differential effects in CHO and PC12 cells.
• Endogenous kinase activity is particulate and associated with vaults, but vaults do not exhibit autophosphorylation.

Conclusions:

• MVP phosphorylation is cell-specific and mediated by associated kinases, not intrinsic to the vault particle.
• These findings highlight the potential importance of cell-specific MVP phosphorylation in regulating vault function.