Co-expression patterns explain how a basic transcriptional role for MYC modulates Wnt and MAPK pathways in colon and lung adenocarcinomas.

A subset of proliferation genes that are associated with origin licensing, firing, and DNA synthesis has been compared to known drivers of colon (COAD) and lung (LUAD) adenocarcinomas using Spearman's rank correlation coefficients. The frequency with which APC, CTNNB1, KRAS, MYC, Braf, TP53, Rb1, EGFR, and cell cycle components have direct or indirect co-expression with the proliferation factors permits identification of their expression relative to the G1-S phase of the cell cycle. Here, adenomatous polyposis coli (APC), a negative regulator of Wnt signaling known to function through MYC, indirectly co-expresses at the same frequency as proliferation genes in both COAD and LUAD, consistent with M phase expression. However, APC is indirectly co-expressed with MYC and is found mutated only in COAD. MYC is thought to function at the interface of transcription and replication, acting through the SWI/SNF chromatin remodeling complex, and increased or decreased expression of MYC can induce or repress tumorigenesis, respectively. These data suggest that transcription of APC during the M phase with low MYC co-expression contributes by an unknown mechanism to APC mutations and Wnt pathway deregulation in COAD and that upper and lower limits of MYC expression, enforced by the cell cycle, may influence cancer differentially. Other Wnt signaling components co-expressed in the low MYC context in COAD also have significantly higher mutation frequencies, supporting the hypothesis. Additionally, Braf is found here to have direct co-expression with multiple proliferation factors in non-EGFR activated LUAD, and EGFR-activated LUAD are completely deregulated with respect to E2F(s) 4/5/6 expression, potentially explaining the low proliferation rates seen in LUAD.Abbreviations: TCGA: The cancer genome atlas; PANCAN: Pan cancer; CDK: Cyclin-dependent kinase; COAD: Colon adenocarcinoma; LUAD: Lung adenocarcinoma; Wnt: Wingless/integrated signaling; MAPK: Mitogen-activated protein kinase; APC: Adenomatous polyposis coli gene; CIN: Chromosomal instability; GS: Genome stabile; MMR: Mismatch repair; mRNA: Messenger RNA; RPKM: Reads per kilobase of transcription per million mapped reads; RSEM: RNA Seq by expectation maximization; FDR: False discovery rate; GTEx: Genotype-Tissue Expression portal; MPF: Maturation-promoting factor; SCF: Skp1-Cul1-F-box; HH: Hedgehog; EMT: Epithelial mesenchymal transition; RB: Retinoblastoma; EGFR: Epidermal growth factor receptor; rs or ρ: Spearman's correlation.