The coding region of the Bloom syndrome BLM gene and of the CBL proto-oncogene is mutated in genetically unstable sporadic gastrointestinal tumors.
Microsatellite instability (MSI) characterizes the hereditary nonpolyposis colorectal cancer syndrome but is also found in sporadic tumors. Frameshifts in microsatellites found in the coding regions (CDRs) of the TGFbeta1-RII, IGFIIR, hMSH3, hMSH6, and BAX genes indicate that MSI is involved in tumorigenesis by targeting genes that are directly implicated in the tumorigenic process. To identify additional genes targeted for MSI, we performed an analysis of the GenBank database that revealed 21 microsatellite repeats located in the CDR of 18 genes (12% of the analyzed sequences) whose function could be potentially associated with the tumorigenic process. Mutational studies of 57 sporadic gastrointestinal tumor DNAs revealed the presence of length variations in three of them: (a) BLM; (b) CBL; and (c) HOXA1. In the BLM gene, we found a frameshift mutation in a polyadenine repeat, whereas in the CBL proto-oncogene, an expansion of a trinucleotide repeat was detected with no translation shift. These alterations were present in 18 and 9%, respectively, of the genetically unstable sporadic gastrointestinal tumors analyzed, but in none of the cancers without the mutator phenotype. These changes were present in the DNA from the tumor but not in that from normal cells of the same patient. The HOXA1 retraction of a trinucleotide repeat was as frequent in both types of cancers and was also found in some normal paired tissues, therefore behaving as a neutral polymorphism. Our data extend the spectrum of unstable microsatellites located in gene CDRs and suggest that BLM and possibly CBL are involved in gastrointestinal tumorigenesis. Based on its proposed function, the BLM gene could represent a link between MSI and chromosomal instability pathways, because MSI targeting of the BLM gene could generate hypermutability and/or chromosomal instability.
Calin
G
G
Department of Experimental and Diagnostic Medicine, University of Ferrara, Italy.
Herlea
V
V
Barbanti-Brodano
G
G
Negrini
M
M
D000251:Adenosine Triphosphatases / Q000235:genetics*; D001816:Bloom Syndrome / Q000235:genetics*; D004265:DNA Helicases / Q000235:genetics*; D005770:Gastrointestinal Neoplasms / Q000235:genetics*; D006801:Humans; D018895:Microsatellite Repeats; D009154:Mutation; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D050721:Proto-Oncogene Proteins c-cbl; D011519:Proto-Oncogenes; D053484:RecQ Helicases; D044767:Ubiquitin-Protein Ligases
C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases; C067419:CBL protein, human