Evaluating the impact of diminished SKP2 expression on chromosome instability and colorectal cancer pathogenesis

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Neudorf, Nicole M.
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Colorectal cancer (CRC) remains the third most commonly diagnosed and second most lethal cancer in Canada. Therefore, gaining a greater understanding of the mechanisms driving cancer initiation and progression is essential before novel treatment strategies can be developed to address the high morbidity and mortality rates associated with CRC. Chromosome instability (CIN), or ongoing changes in chromosome complements, occurs in ~85% of CRCs and is a proposed driver of cancer development. Despite these associations, the aberrant genes underlying CIN remain elusive. Preliminary screens of potential CIN genes identified S-phase Kinase-associated Protein 2 (SKP2) as a strong candidate CIN gene warranting further investigation. SKP2 encodes an F-box protein, a subunit of the SCF complex of ubiquitylation proteins that selectively targets key protein substrates for ubiquitylation and degradation by the 26S proteasome. The impact reduced SKP2 expression has on CIN, cellular transformation and oncogenesis remains unknown. Accordingly, the current study seeks to investigate the impact reduced SKP2 expression has on CIN in a CRC context. I hypothesize that decreased SKP2 expression induces CIN that promotes cellular transformation that contributes to CRC development. I addressed this hypothesis through the execution of two experimental research aims evaluating the short- and long-term impact diminished SKP2 expression has in malignant and non-malignant colonic epithelial cell contexts. Specifically, short-interfering RNA (siRNA) and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR Associated Protein 9 (Cas9) approaches were coupled with single-cell quantitative imaging microscopy (scQuantIM) to assess changes in CIN-associated phenotypes. Analyses of SKP2 silenced cells revealed significant increases in nuclear areas, micronucleus formation and the abundance of cells with aberrant karyotypes relative to silencing controls. Moreover, all SKP2 clones exhibited significant and dynamic changes in nuclear area distributions and micronucleus formation over a 10-week timeframe. Finally, chromosome enumeration data showed that SKP2 clones displayed ongoing changes in chromosome complements over time (i.e., CIN) that enabled the acquisition of cellular transformation phenotypes including increased proliferation, clonogenic growth, and anchorage-independent growth. Collectively, these data identify SKP2 as a novel CIN gene in clinically relevant models and highlight its potential pathogenic implications in CRC development.
Chromosome Instability