Frameshift mutations of vacuolar protein sorting genes in gastric and colorectal cancers with microsatellite instability

Abstract

Vacuolar protein sorting plays crucial roles in the traffic of molecules between cellular organelles. Although involvement of vacuolar protein sorting proteins in cancer is known, genetic alterations of VPS genes have not been reported in cancers. We found that VPS4B, VPS13A, VPS13B, VPS13C, VPS33A, VPS35, VPS37B, VPS37D, VPS41, and VPS54 have mononucleotide repeats in their coding sequences. To see whether these genes are mutated in cancers with microsatellite instability, we analyzed the mononucleotide repeats in 30 gastric cancers with high microsatellite instability, 13 gastric cancers with low microsatellite instability, and 45 gastric cancers with stable microsatellites and 40 colorectal cancers with high microsatellite instability, 14 colorectal cancers with low microsatellite instability, and 45 colorectal cancers with stable microsatellites by single-strand conformation polymorphism. We found mutations of VPS13A, VPS13B, VPS13C, VPS33A, VPS35, VPS37B, VPS41, and VPS54 in 9, 3, 12, 3, 5, 9, 2, and 2 cancers, respectively, all in cancers with high microsatellite instability. The gastric cancers and colorectal cancers with high microsatellite instability harbored one or more mutations of the VPS genes in 53.3% and 50.0%, respectively. Loss of Vps13A expression was observed in 30% of the gastric cancers and 35% of the colorectal cancers, whereas loss of Vps35 was observed in 55% of the gastric cancers and 55% of the colorectal cancers. Our data indicate that frameshift mutations of VPS genes and losses of expression of Vps13A and Vps35 proteins are common in gastric cancers and colorectal cancers with high microsatellite instability and suggest that these alterations might contribute to development of cancers with high microsatellite instability by deregulating vacuolar protein sorting proteins.