Abstract 3024: Lack of CK1δ increases DNA damage and genomic instability due to defects in DNA repair and mitotic checkpoints

Abstract

Abstract Casein kinase 1 delta (CK1δ) is a conserved serine/threonine protein kinase that regulates diverse cellular processes including vesicle trafficking and circadian rhythm. We previously reported that CK1δ is a mediator of Wnt-3a-dependent neurite outgrowth (Greer and Rubin, JCB, 2011) and ciliogenesis (Greer et al. MBoC, 2014). Mice that lack Csnk1d exhibit a perinatal lethal phenotype and typically weigh 30-50% less than their wild type littermates, however, the exact causes of death and small size are unknown. We hypothesized that the absence of CK1δ contributes to cellular stresses that adversely affect cell survival. Mouse embryonic fibroblasts (MEFs) were collected from mice homozygous for a Csnk1d floxed allele, and MEFCsnk1d null cells were generated by infection with adenovirus (Ad) expressing Cre. As control, MEFCtl. cells were produced by infection with Ad-GFP. In addition, MEFCtl cells were treated with CK1δ siRNA reagents to transiently suppress endogenous expression. Cells were analyzed by confocal microscopy, western blotting and flow cytometry. At early passage (P2), many MEFCsnk1d null cells had detached from the culture dish, raising the possibility of cell death. Subsequent MTS assay confirmed a significantly lower cell viability of MEFCsnk1d null cells compared to MEFCtl cells. MEFCsnk1d null cells (P3) exhibited a larger sub-Go fraction (64%) than MEFCtl cells (34%) in flow cytometric analysis. γ-H2AX staining and comet assay confirmed significant DNA damage in MEFCsnk1d null cells. MEFCsnk1d null cells exhibited micronuclei, a characteristic of genomic instability. Similarly, abrogation of CK1δ expression in MEFCtl cells induced micronuclei formation in response to DNA damage triggered by doxorubicin, suggesting that the absence of CK1δ increases susceptibility to genotoxic exposure. Chk1, a kinase with a major role in DNA damage response, and its downstream substrate, Cdc2/CDK1 kinase, were inhibited in MEFCsnk1d null cells as well as in MEFCtl cells transfected with CK1δ siRNA, suggesting that CK1δ is required for the G2/M mitotic checkpoint. Hydroxyurea-induced Chk1 activation was also impaired in cells lacking CK1δ, and re-expression of CK1δ rescued the phenotype. Together, the data indicate that CK1δ is required for efficient repair of DNA damage and the proper functioning of mitotic checkpoints. The mechanism(s) responsible for these activities are currently under investigation. Citation Format: Yoshimi E. Greer, Bo Gao, Yingzi Yang, Stanley Lipkowitz, Jeff S. Rubin. Lack of CK1δ increases DNA damage and genomic instability due to defects in DNA repair and mitotic checkpoints. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3024. doi:10.1158/1538-7445.AM2015-3024