A novel centrosome protein involved in regulation of microtubule formation

Abstract

KIAA0092 is a former hypothetical protein possessing two coiled-coil segments. Upon over-expression in mammalian cells, KIAA0092 localizes and stabilizes microtubules (MTs) forming a remarkably stable ‘basket-like’ structure. Its C-terminal-half mutant retains the ability to stabilize MTs, whereas, the N-terminal-half localizes to centrosomes and appears to be involved in homo-multimerization. No basket structure but random aggregation was observed in cells pre-treated by nocodazole, implying that KIAA0092 hinders MT dynamics through inhibition of depolymerization. In in vitro tubulin polymerization studies, 1.25 uM recombinant KIAA0092 initiates polymerization of tubulin [12.5 uM] resulting in remarkably stable MTs, which tolerate prolonged storage at room temperature. In addition to MT formation, excess KIAA0092 leads to a 2-6 fold increase in OD350 as compared to MTs alone. Electron microscopy revealed that this increase is caused by aggregation of MTs mediated by KIAA0092. Localization of endogenous KIAA0092 at centrosomes was detected by two newly generated antibodies. Low-level expression of exogenous KIAA0092, insufficient to produce the basket structure and localized only to centrosomes, decreased the presence of mitotic cells, perhaps due to hindrance of endogenous protein function. Centrosomes have been shown to play a crucial role in MT regulation during mitosis. Knowing that KIAA0092 nucleates and enhances MT formation and that endogenous KIAA0092 is located at centrosomes, we propose that KIAA0092 plays a significant role in regulation of MT dynamics and mitosis during the cell cycle. (Supported by NIH PO1 HL 48807)