Oral squamous cell carcinoma is a prominent cancer worldwide, particularly in Taiwan. By integrating omics analyses in 50 matched samples, we uncover in Taiwanese patients a predominant mutation signature associated with cytidine deaminase APOBEC, which correlates with the upregulation of APOBEC3A expression in the APOBEC3 gene cluster at 22q13. APOBEC3A expression is significantly higher in tumors carrying APOBEC3B-deletion allele(s). High-level APOBEC3A expression is associated with better overall survival, especially among patients carrying APOBEC3B-deletion alleles, as examined in a second cohort (n = 188; p = 0.004). The frequency of APOBEC3B-deletion alleles is ~50% in 143 genotyped oral squamous cell carcinoma -Taiwan samples (27A3B−/−:89A3B+/−:27A3B+/+), compared to the 5.8% found in 314 OSCC-TCGA samples. We thus report a frequent APOBEC mutational profile, which relates to a APOBEC3B-deletion germline polymorphism in Taiwanese oral squamous cell carcinoma that impacts expression of APOBEC3A, and is shown to be of clinical prognostic relevance. Our finding might be recapitulated by genomic studies in other cancer types.
Mass Spectrometry Data Sets, Provided Below
The APOBEC-associated mutational signature enriched in the OSCC-Taiwan cohort was investigated to determine if this mutational signature might correlate with tumor-related alterations in APOBEC expression.
Corresponding enrichment of A3A-specific peptides in tumor proteomes was assessed by iTRAQ (isobaric Tags for Relative and Absolute Quantification) mass spectrometry protein quantification methods in 38 normal / tumor paired tissue samples. Peptides were digested, labeled by iTRAQ, and fractionated by on-line 2D-HPLC to 44 fractions. Each dataset (labeled as OSCC-Pxx, example OSCC-P01) contains 44 raw mass spectrometry data files (LTQ-Orbitrap ELITE). The iTRAQ 114 reagent was used to label the digestion products of 30-pairs of OSCC tissues, and iTRAQ 115 and 116 reagents were used to label peptides of non-tumor tissue and tumor tissue, respectively. The APOBEC3A (A3A) coding region is part of a APOBEC3 gene cluster at 22q13.