BACKGROUND

The Condensin II complex's known function is in chromosomal segregation and assembly. Leiserson et al. demonstrated that Condensin II was enriched for mutations in a pan-cancer sweep, particularly lung cancer; one gene, NCAPH2, had a notable mutation cluster. Venet et al. created metaPCNA, a robust proliferation-based gene expression (GE) signature from 36 tissues, which includes 4 Condensin genes. This suggests that Condensin II expression is correlated with proliferation. We hypothesize that Condensin II influences cancer proliferation in two ways, and demonstrate evidence for the first: 1) rare stabilizing subunit mutations or 2) pairing of high Condensin II expression with a driver mutation that affects pathways controlling Condensin II activity.

METHODS

Using the TCGA lung adenocarcinoma (LUAD) gene expression dataset (n=571), we calculated the Condensin II index (mean expression of 5 genes) and the metaPCNA index (median expression of 131 genes). Pearson correlation between indices was calculated to assess information overlap between gene signatures. For outcome assessments, scores were split into tertile labels (high, middle, low). Linear-by-linear testing was assessed for score agreement. Unsupervised hierarchical clustering of the top 2,500 most variant genes with samples labeled by index tertile inclusion was completed for both indices.

After noting the similarity between indices, we tested Condensin II as a driver of proliferation by running overexpression assays using the rate limiting subunit of the complex, NCAPH2. Plasmids with NCAPH2, both wildtype and engineered to have the R551P mutation identified by Leiserson, were transfected into RPE1 cells, a telomere elongation immortalized cell line with a ‘normal' proliferation profile. We had 3 conditions 1) myc-tagged control, 2) wild-type NCAPH2, and 3) R551P mutated NCAPH2, utilizing Incucyte imaging for 3 days after a 1-day rest to assess the proliferation of cells.

RESULTS

The Condensin II index and metaPCNA index were strongly associated (correlation = 0.85). Cluster analysis by either the metaPCNA or Condensin II index demonstrated that the lowest tertile tends to separate from the middle and highest tertile. Samples had a high overlap of tertile labels between the 2 indices (n labels matched =406, n not matched = 165, z= 18.57, p= <2.2*10-16).

A 72-hour time course of the 3 transfected cell lines demonstrated that overexpression of R551P mutated NCAPH2was associated with an increase in proliferation, while wild-type NCAPH2did not differ significantly from the myc-tagged control.

CONCLUSIONS

Condensin II index is a simple, 5-gene signature strongly associated with a known proliferation signature and tumor expression patterns. A potentially stabilizing mutation to NCAPH2, R551P, increases proliferation potential in cell line experimentation, but overexpression of wild-type NCAPH2does not. Condensin II may be a driver of cancer proliferation.

Citation Format: Ellen L. Nutter, Emily S. Weyburne, Jeffrey Thompson, Jennifer A. Doherty, Giovanni Bosco. Condensin II complex as a potential driver of cancer proliferation [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 4310.