Landscape of genomic alterations in cervical carcinomas

Abstract

Cervical cancer is responsible for 10-15% of cancer-related deaths in women worldwide. The aetiological role of infection with high-risk human papilloma viruses (HPVs) in cervical carcinomas is well established. Previous studies have also implicated somatic mutations in PIK3CA, PTEN, TP53, STK11 and KRAS as well as several copy-number alterations in the pathogenesis of cervical carcinomas. Here we report whole-exome sequencing analysis of 115 cervical carcinoma-normal paired samples, transcriptome sequencing of 79 cases and whole-genome sequencing of 14 tumour-normal pairs. Previously unknown somatic mutations in 79 primary squamous cell carcinomas include recurrent E322K substitutions in the MAPK1 gene (8%), inactivating mutations in the HLA-B gene (9%), and mutations in EP300 (16%), FBXW7 (15%), NFE2L2 (4%), TP53 (5%) and ERBB2 (6%). We also observe somatic ELF3 (13%) and CBFB (8%) mutations in 24 adenocarcinomas. Squamous cell carcinomas have higher frequencies of somatic nucleotide substitutions occurring at cytosines preceded by thymines (Tp*C sites) than adenocarcinomas. Gene expression levels at HPV integration sites were statistically significantly higher in tumours with HPV integration compared with expression of the same genes in tumours without viral integration at the same site. These data demonstrate several recurrent genomic alterations in cervical carcinomas that suggest new strategies to combat this disease.

Fig. 1. Relationship of mutational spectrum and rates with clinicopathological characteristics in cervical carcinoma

All panels are aligned with vertical tracks representing 115 individuals. The data is sorted in order by histology (middle panel) and total mutational rate (top panel). The relative frequencies of nucleotide mutations occurring at cytosines preceeded by thymines (Tp*C) or at cytosines followed by guanines (*CpG) sites are depicted in red and orange respectively, on the second panel. The bottom heatmap shows the distribution of mutations in significantly mutated genes (q<0.1) in squamous cell carcinomas and adenocarcinomas in the order listed in Table 1. TP53, ERBB2 and KRAS were significant recurrence (q<0.1) among cancer driver genes reported in COSMIC.

Fig. 2. Novel recurrent somatic mutations in cervical carcinoma

The locations of somatic mutations in novel significantly mutated genes in 115 cervical carcinoma, FBXW7, MAPK1, HLA-B, EP300, NFE2L2 and ELF3 are shown in the context of protein domain models derived from UniProt and Pfam annotations. Numbers refer to amino acid residues. Each filled circle represents an individual mutated tumor sample: missense and silent mutations are represented by filled black and grey circles, respectively while nonsense, frameshift, and splice site mutations are represented by filled red circles and red text. Domains are depicted with various colors with an appropriate key located on the right hand of each domain model.

Fig. 3. Relationships between HPV integration, copy number amplifications and gene expression in cervical carcinoma

Panel (a) shows comparative histograms of true and simulated genomic distances between HPV integration sites and the nearest copy number amplification (log segmean difference >0.5). Panel (b) shows boxplots of gene expression levels across 79 cervical tumors for 41 genes with chimeric human-HPV read pairs. The expression levels for tumors with HPV integration in the respective genes are highlighted in red circles. Panel (c) shows scatter plots comparing copy number alterations and gene expression levels across 79 tumors in selected integration site genes. The red circles represent data for the tumors with HPV integration events involving the respective genes.