Abstract 3453: PAK6 localizes to centrosome and modulates centrosome homeostasis
Authors: Jia Houjun , Chapagai Danda , Mallow John , Perttunen Michael D. , Iragavarapu Vijaya , Wei Jianning , Lu Michael L. 
Published: August 2018

Centrosome abnormalities are linked to genomic instability and are considered one possible cause of cancer progression. In prostate and breast cancer, centrosome over-duplication is correlated with lymph node and distant metastasis. In prostate cancers, centrosome amplification is a useful predictor of tumor recurrence, highlighting its potential role in promoting advanced disease. PAK6 was identified as an androgen receptor (AR) interacting protein. It has been determined that activated PAK6 plays an active role in promoting hormone-regulated prostate cancer metastatic phenotypes such as upregulating cell motility and invasiveness. Several lines of evidence indicate that PAK6 is overexpressed in advanced cancers including prostate, colon and liver cancers. The up-regulated expression of PAK6 in advanced diseases underscores its potential role in disease progression.

Using a novel anti-PAK6 antibody readily recognizes the native PAK6 protein, we determined that PAK6 localizes at centrosome and in some cell types also at plasma membrane. This observation revised our previous view of PAK6 as a soluble cytoplasmic protein. Ectopically expression of PAK6 leads to hyperploidy in LNCap cells. We hypothesized that aberrant PAK6 expression plays a critical role in the development of hyperploidy. In current study, we characterized the role of PAK6 in the dysregulation of centrosome-triggered hyperploidy in cancer cells. PAK6 centrosome localization was determined by co-staining of PAK6 with centrosome marker γ-tubulin using immunofluorescence microscopy of a pair of mouse embryo fibroblasts (MEF) derived either from WT mice (MEF-WT) or from PAK6-null mice (MEF-KO). PAK6-centrosome association was also confirmed biochemically by co-fractionation of PAK6 with γ-tubulin in centrosomal subcellular-fractions using a sucrose gradient. Down-regulation of PAK6 expression by lentivirus mediated shRNA promotes centrosome amplification with increased centrosome size in LNCap and MCF7 cells. Accelerated microtubule aster regrowth following nocodazole-induced depolarization was observed in MEF KO cells in as compared to MEF WT cells. Reciprocally, the inhibitory effects of PAK6 overexpression on aster growth was demonstrated in tetracycline inducible U2OS cells.

Our results indicate that PAK6 on one hand promotes aneuploidy, but on the other hand its expression suppresses centrosome amplification and microtubule dynamics. These apparent incompatible results suggest that PAK6 functions at multiple levels that in one hand it regulates centrosome amplification and microtubule dynamics, and on the other hand it may be involved in regulating the chromosome segregation and cytokinesis. The net effects of PAK6 expression may be context dependent.

Citation Format: Houjun Jia, Danda Chapagai, John Mallow, Michael D. Perttunen, Vijaya Iragavarapu, Jianning Wei, Michael L. Lu. PAK6 localizes to centrosome and modulates centrosome homeostasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3453.