MRE11 expression is impaired in gastric cancer with microsatellite instability.
Gastric carcinomas (GCs) with high-level microsatellite instability (MSI-H) are characterized by widespread mutations at coding and non-coding mononucleotide repeats. Deletions at coding mononucleotide tracts are predicted to cause frameshift mutations and alter normal protein functions. Mutations affecting non-coding mononucleotide repeats may lead to functional consequences if they occur in gene regulatory regions. To investigate whether mutations in non-coding polypyrimidine tracts within cancer-related genes may contribute to the phenotype of MSI-H GCs, we analysed the poly(T)11 tract constituting an accessory splicing signal within the intron 4 of the MRE11 gene. Mutations at the intronic MRE11 poly(T)11 were evaluated by PCR-based assay in 27 MSI-H, 22 MSI-low and 29 MSI-negative GCs derived from a well-characterized series of GCs identified in a high-risk area in Tuscany, Central Italy. Deletion of 2 and 1 bp at the MRE11poly(T)11 were identified in 33 and 48% MSI-H GCs, respectively. Biallelic mutations were frequently observed (77%) in GCs harbouring 2 bp deletions. The presence of MRE11poly(T)11 2 bp deletion was associated with a totally absent or strongly reduced MRE11 immunostaining (P < 0.001) and with a positive GC family history (P = 0.046). Immunoblotting assays confirmed the absence of MRE11 expression in GCs with a 2 bp deletion. The relatively high frequency of the MRE11poly(T)11 mutations, the occurrence of biallelic mutations and the evidence of loss of protein expression indicate MRE11 as novel mutational target in MSI-H GC. Overall, our results indicate that MSI-associated mutations occurring in non-coding repeats may affect protein expression in MSI-H GC.
Department of Experimental Medicine and Pathology, University La Sapienza, 00161 Rome, Italy. ottini@yahoo.com
Laura
L
Ottini
Mario
M
Falchetti
Calogero
C
Saieva
Manola
M
De Marco
Giovanna
G
Masala
Ines
I
Zanna
Milena
M
Paglierani
Giuseppe
G
Giannini
Alberto
A
Gulino
Gabriella
G
Nesi
Renato
R
Mariani Costantini
Domenico
D
Palli
D000368:Aged; D016022:Case-Control Studies; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins / Q000235:genetics*; D005260:Female; D016368:Frameshift Mutation / Q000235:genetics*; D017353:Gene Deletion; D042822:Genomic Instability; D006801:Humans; D015151:Immunoblotting; D007438:Introns / Q000235:genetics*; D000076228:MRE11 Homologue Protein; D008297:Male; D018895:Microsatellite Repeats; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011743:Pyrimidines; D012326:RNA Splicing; D012091:Repetitive Sequences, Nucleic Acid; D013274:Stomach Neoplasms / Q000235:genetics* / Q000473:pathology; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; D011743:Pyrimidines; D000076228:MRE11 Homologue Protein