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We determined the most commonly mutated genes in five cancer genome atlas (TCGA) datasets. Many of these genes were extraordinarily large, as are many cancer fusion gene partners. And many of these genes had cytoskeletal related functions. We further determined that these genes were distributed into high and low frequency mutation groups largely according to overall rate of gene-occurrence in the high and low mutation frequency groups, as was also the case with common metastasis and tumor suppressor genes. Oncoproteins were selectively mutated in the low mutation frequency groups in colon and lung datasets. Thus, genes that have very large coding regions and may impact the cytoskeleton are more commonly mutated than are common metastasis and tumor suppressor genes in both high and low frequency mutation groups. These analyses raise questions related to cell shape: (i) Are cancer cells often spherical because cytoskeletal-related proteins are large mutagen targets? (ii) Is drug-resistance facilitated by relatively common mutant proteins that lead to round cells, with altered cell physiology or reduced surface to volume ratios that could reduce intra-cellular drug concentrations?

Background Forty years ago the actin cytoskeleton was determined to be disrupted in fibroblasts from persons with DNA repair-defective, hereditary colon cancer, with no clear connection between the cytoskeleton and DNA repair defects at that time. Recently, the large number of sequenced genomes has indicated that mammalian mutagenesis has a large stochastic component. As a result, large coding regions are large mutagen targets. Cytoskeletal protein-related coding regions (CPCRs), including extra-cellular matrix proteins, are among the largest coding regions in the genome and are indeed very commonly mutated in cancer. Methods To determine whether mutagen sensitivity of the actin cytoskeleton could be assessed experimentally, we treated tissue culture cells with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and quantified overall cytoskeleton integrity with rhodamine-phalloidin stains for F-actin. Results The above approach indicated cytoskeletal degradation with increasing mutagen exposure, consistent with increased mutagenesis of CPCRs in TCGA, smoker samples, where overall mutation rates correlate with CPCR mutation rates (R2 = 0.8694; p

Oncoprotein genes are over-represented in statically defined, low mutation-frequency fractions of cancer genome atlas (TCGA) datasets, consistent with a higher driver mutation density.We developed a "continuously variable fraction" (CVF) approach to defining high and low mutation-frequency groups.Using the CVF approach, an oncoprotein set was shown to be associated with a TCGA, low mutation-frequency group in nine distinct cancer types, versus six, for statically defined sets; and a tumor-suppressor set was over-represented in the low mutation-frequency group in seven cancer types, notably including BRCA. The CVF approach identified single-mutation driver candidates, such as BRAF V600E in the thyroid cancer dataset. The CVF approach allowed investigation of cytoskeletal protein-related coding regions (CPCRs), leading to the conclusion that mutation of CPCRs occurs at a statistically significant, higher density in low mutation-frequency groups. Supporting online material for this article can be found at www.universityseminarassociates.com/Supporting_online_material_for_scholarly_pubs.php.