Variation in mutation rate and direction between tetranucleotide STR loci in human colorectal carcinomas

Area of Science:

• Genetics
• Cancer Research
• Molecular Biology

Background:

• Replication error (RER) involves mutation events within repetitive DNA segments.
• Understanding RER is crucial for cancer research, particularly in colorectal adenocarcinomas.
• Investigating differences in mutation outcomes across various short tandem repeat (STR) loci is essential.

Purpose of the Study:

• To investigate the somatic mutation rate and new tumor allele size distribution in four tetranucleotide STRs.
• To reveal differences in mutation outcomes between distinct STR loci.
• To analyze RER in a large cohort of unselected colorectal adenocarcinomas.

Main Methods:

• DNA extraction from blood and tumor samples of 217 colorectal adenocarcinoma patients.
• Analysis of four tetranucleotide STR loci: HUMTHO1, HUMFES/FPS, HUMVWA31/A, and HUMF13A1.
• Comparison of mutation rates and allele size distributions between blood and tumor DNA.

Main Results:

• Mutations were detected at all four analyzed STR loci.
• Substantial differences in mutation rates and directions (expansion vs. contraction) were observed between STR loci.
• The majority of RER events involved the gain or loss of a single repeat unit.
• New tumor alleles predominantly corresponded to known population alleles, composed of integer repeat units.
• No statistically significant size bias was found in mutating alleles compared to population allele distribution.

Conclusions:

• Significant locus-specific variations exist in somatic mutation rates and outcomes for STRs during colorectal carcinogenesis.
• RER in colorectal adenocarcinomas primarily results in minor alterations (single repeat changes) at STR loci.
• The observed RER patterns do not introduce significant size bias in tumor alleles relative to the general population.