Mutational analysis of caspase 1, 4, and 5 genes in common human cancers

Summary

Mounting evidence indicates that deregulation of apoptosis is involved in the mechanisms of cancer development. Mutations of genes encoding caspases, the executioners of apoptosis, have been detected in human cancers, indicating inactivation of apoptosis by the mutations of caspase is an important mechanism in cancer development. The aim of this study was to see whether genes encoding human caspases 1, 4, and 5 are mutated in human cancers. We analyzed the entire coding region and all splice sites of human caspase 1, 4, and 5 genes for the detection of somatic mutations in 337 human cancers, including 103 colorectal, 54 gastric, 60 breast, 60 hepatocellular, and 60 lung carcinomas by a single-strand conformation polymorphism assay. We detected 2 (0.6%) caspase-1, 2 (0.6%) caspase-4, and 15 (4.4%) caspase-5 mutations in the 343 cancers. The mutations were detected in 11 gastric carcinomas (2 caspase-1 and 9 caspase-5 mutations), 6 colorectal carcinomas (2 caspase-4 and 4 caspase-5 mutations), 1 breast carcinoma (1 caspase-5 mutation), and 1 lung carcinoma (1 caspase-5 mutation). The mutations consisted of 11 mutations in exons and 8 mutations in noncoding sequences. The 11 mutations in the exons consisted of 3 missense, 1 silent, and 7 frameshift mutation(s). Of note, most (6/9) of the caspase-5 mutations in the coding sequences were detected in microsatellite instability (MSI)-positive cancers. These data indicate that somatic mutations of caspase-1 and caspase-4 genes are rare in common solid cancers. In addition, the data indicate that caspase-5 gene is commonly mutated in the MSI-positive cancers, and suggest that inactivation of caspase-5 may play a role in the tumorigenesis of MSI-positive cancers.

Introduction

Apoptosis is a cellular suicide mechanism that plays a critical role in development and tissue homeostasis in organisms [1], [2]. The final stage of apoptosis occurs through activation of a family of cysteine proteases which cleave the substrates at aspartate residues, known as caspases [3], [4]. The caspase family contains 13 mammalian isoenzymes, of which 11 human isoenzymes are known currently [1], [3], [4]. Interleukin-1β converting enzyme (ICE; caspase-1) is a prototypical caspase and was initially identified as a protease for the proteolytic maturation of prointerleukin-1β [5]. Caspases 1, 4, and 5 have similar structures and are considered as an ICE subfamily [3], [4], [5], [6], [7]. The ICE subfamily caspases play important roles in both inflammation and apoptosis [8].

Deregulation of apoptosis may be directly involved in several human diseases, including degenerative diseases, cancers, and AIDS [1]. It is well known that clonal expansion and tumor growth are the results of the deregulation of intrinsic proliferation and apoptosis [9]. Failure of apoptosis could allow the survival of transformed cells that are prone to undergo further genetic damage and play an important role in the pathogenesis of neoplasia. Either inactivation of proapoptotic pathway or activation of antiapoptotic pathway results in failure of apoptosis, thereby promoting cancer cell survival. Somatic mutations of the genes encoding proapoptosis proteins, including the death receptor genes and caspase genes, have been reported in human cancers [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. Among the caspase genes, mutations of caspases 3, 5, 6, 7, 8, 9, and 10 have been reported in human cancer tissues [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. The mutated caspases showed reduced apoptosis activities compared with those of wild-type caspases [16], [19], [21], suggesting that inhibition of apoptosis by caspase gene mutations might play an important role in evasion of apoptosis of cancer cells.

Somatic mutation of the caspase-5 gene has been detected in colon carcinomas, gastric carcinomas, lung carcinomas, and acute leukemias, and all of the mutations were detected in a mononucleotide repeat (A)₁₀ in exon 2 [12], [13], [14]. However, somatic mutation of DNA sequences in other coding region of caspase-5 besides the repeat sequences (A)₁₀ has not yet been reported in cancers. In addition, no somatic mutation of caspase-1 or caspase-4 has yet been reported in human cancers. In the present study, to explore the possibility that the alterations of caspase 1, 4, and 5 genes might play roles in development of human cancers, we investigated the presence of the mutations in common human carcinomas.