Date of Award

10-20-2015

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

Swan, Andrew

Keywords

Apoptosis, Cell cycle, Cyclin A, polyploidy, Skp2

Rights

CC BY-NC-ND 4.0

Abstract

Spontaneous duplications of the genome give rise to polyploid cells and polyploidy can lead to aneuploidy. Aneuploidy is a well-documented phenomenon that could cause cancer. Therefore, a thorough knowledge of how cells maintain diploidy can help us prevent cancer. E3 ubiquitin ligases regulate the cellular levels of a wide variety of oncoproteins. The multi-protein complex, SCF (Skp1-Cullins-F-box) is an E3 ligase that is responsible for ubiquitination-mediated degradation of a large number of proteins involved in cell cycle regulation, transcription and tumor suppression. S‐phase kinaseassociated protein‐2 (Skp2) is the receptor of the SCF complex that promotes the degradation of specific target proteins. The SCFSkp2 targets a wide variety of proteins including tumor suppressor protein p27. Cdc kinase subunit 1 (Cks1) is a small Cyclin – dependent kinase (CDK) interacting protein that is essential for Skp2 mediated degradation of p27. We have generated null alleles of Skp2 and Cks1 (Cks85A) in fruit flies and found that loss of these genes results in polyploidy and abnormal mitosis. These genes are also essential for normal growth of the fruit fly. Skp2 was first identified as a protein that associates with Cyclin A/ Cdk2. We provide the evidence for the first time that Skp2 is required in G2 to protect Cyclin A from premature degradation. Furthermore, our data for the first time suggest a mitotic role of Skp2. We show that Skp2 is required for maintaining the levels of mitotic cyclins and is also required for mitotic entry. Skp2 and Cks85A mutant imaginal discs undergo extensive apoptosis. We provide the first evidence of a stress response pathway that is activated upon the loss of Skp2. Our results suggest that loss of Skp2 results in polyploidy related abnormal mitosis that triggers the spindle assembly checkpoint and the DNA damage response. We also provide evidence of JNK pathway activation and autophagy in the Skp2 null background. Taken together, our finding suggests a novel Skp2 –Cyclin A interaction that plays an important role in maintaining diploidy and thus, genome stability.

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