A Yeast Synthetic Lethal Screen Identifies A Conserved Interaction Between Plk1 And Cks1b Affecting Cancer Cell Viability

The CKS1b gene is located on chromosome 1q21 and is frequently amplified in breast, lung and liver cancers. CKS1b codes for a conserved regulatory subunit of cyclin-CDK complexes that functions at multiple stages of cell cycle progression. We used a high throughput screening protocol to mimic cancer-related over-expression in Saccharomyces cerevisiae mutants to identify genes whose functions become essential only when CKS1 is over- expressed, a genetic interaction termed synthetic dosage lethality (SDL). Mutations in genes affecting the mitotic entry checkpoint and genes affecting mitotic exit are evident among the SDL interactions identified. The mitotic entry checkpoint controls the stability of the mitotic inhibitor Swe1 (Human WEE1), resulting in delayed mitosis when cell polarity is disrupted. Swe1 is a tyrosine kinase that inhibits the cyclin-dependent kinase (CDK) complex by phosphorylation of a conserved tyrosine-19 on Cdc28 (Human CDK1). We find that the SDL interaction between Cks1 and the mitotic entry checkpoint requires both Swe1 and the Cdc28 tyrosine-19 residue. The mitotic exit network is a signaling cascade that controls post-anaphase inhibition of CDK activity necessary for progression into G1. Since the polo-like kinase Cdc5 (Human PLK1) functions in both the mitotic entry and mitotic exit pathways, we investigated the effect of targeting PLK1 in breast cancers with varying expression of CKS1b. We analyzed published datasets and found that growth inhibition resulting from PLK1 knockdown was strongly correlated with increased CKS1b expression levels in breast cancer cell lines [Marcotte, R., Brown, K., Suarez, F., u0026 Sayad, A. (2012). Cancer Discovery, 2:172]. We independently confirmed sensitivity to PLK1 knockdown in 8 breast cancer cell lines in which 3 of 4 sensitive lines had high CKS1b expression and 3 of 4 insensitive lines had low CKS1b expression. We modified CKS1b expression in hMEC cells and showed that increased expression enhanced apoptosis upon PLK1 knockdown while decreased CKS1b expression abrogated sensitivity. Thus identification of a yeast synthetic dosage lethal (SDL) interactions identifies a conserved interactions that may be targeted to kill cancer cells. Citation Format: Robert J. Reid, Xing Du, Ivana Sunjevaric, Vinayak Rayannavar, John Dittmar, Matthew Maurer, Rodney Rothstein. A yeast synthetic lethal screen identifies a conserved interaction between PLK1 and CKS1b affecting cancer cell viability. [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 693. doi:10.1158/1538-7445.AM2015-693