Abstract 1074: A novel functional relationship between Aurora A kinase and LIM kinase1: a synergistic role in the mitotic process

Abstract

Aurora A kinase (AurKA), a serine/threonine kinase, plays an essential role in centrosome separation and mitotic spindle assembly. During late G2, the LIM domain containing protein, Ajuba, binds to AurKA allowing for its activation through autophosphorylation. Activated AurKA then phosphorylates key proteins in the centrosomes leading to centrosome maturation. Our earlier studies indicated a possible role of a LIM domain containing serine/threonine and tyrosine kinase, LIM kinase 1 (LIMK1), in the mitotic process. LIMK1 becomes catalytically active through phosphorylation at T508 by PAK and ROCK. Phosphorylated LIMK1 modulates actin and microtubule (MT) dynamics through inactivation of ADF family protein cofilin and MT-binding protein p25/Tpppα, and colocalizes with γ-tubulin to the centrosomes during early stages of mitosis. In this study, we present a novel functional association between AurKA and LIMK1 in prostate cancer cells. Ectopic expression of phospho-mimic mutant of LIMK1 showed a positive correlation with expression of AurKA in benign prostatic hyperplasia (BPH-1) cells. Immunofluorescence analysis showed colocalization of phosphorylated LIMK1 with AurKA to the centrosomes in PC3 prostate cancer cells, which endogenously overexpress LIMK1 compared to BPH-1 cells. shRNA mediated knockdown of LIMK1 decreased the level of phosphorylated AurKA when compared to the non-targeting shRNA control. Microscopic analysis of cells with knocked down LIMK1 showed disorganized spindle morphology with phosphorylated AurKA localized to multiple spindle poles. No abnormalities in localization of phosphorylated AurKA to the spindle poles were noted in cells transfected with non-targeting shRNA. LIMK1 physically associates with AurKA in immunoprecipitable complexes in extracts from PC3, transfected BPH-1 and RWPE1 (normal prostate cell line) cells expressing phospho-mimic mutant of LIMK1. Further analysis of expression of truncated LIMK1 showed that AurKA binds to LIMK1 through its LIM domains. LIMK1 acts as a substrate of AurKA as recombinant AurKA phosphorylated catalytically inactive LIMK1 in kinase assays. This data suggests that the functions of AurKA in mitotic cells may be mediated in part by activation of LIMK1 as both proteins are targeted to the centrosomes in early mitotic phases; and LIMK1 may play a role in regulation of AurKA functions. Our study indicates for the first time that AurKA and LIMK1 are functionally cooperating in the mitotic events in prostate cancer cells. Overexpression of AurKA has been noted in a variety of cancers including prostate cancer and currently, small molecule inhibitors targeting Aurora A are undergoing clinical trials as possible cancer therapeutics. This study suggests that targeted inhibition of LIMK1 may have the added benefit of inhibition of Aurora A kinase in cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1074.