Assuntos
Tumor Desmoplásico de Pequenas Células Redondas , Neoplasias , Humanos , Tumor Desmoplásico de Pequenas Células Redondas/genética , Tumor Desmoplásico de Pequenas Células Redondas/terapia , Tumor Desmoplásico de Pequenas Células Redondas/patologia , Peritônio/patologia , Fusão Gênica , Proteínas de Fusão Oncogênica/genética , Proteínas WT1/genéticaRESUMO
Based on the principle of nonsense-mediated mRNA decay, we sought to identify MLH1 or MSH2-deficient colorectal tumours through relative quantification of mRNA expression with real-time PCR (RT-PCR) analysis. MLH1 and MSH2 mRNAs were almost equally expressed as defined by MLH1 to MSH2 transcript ratio (mean 1.41) in microsatellite stable, mismatch repair (MMR) proficient tumours (n = 16). A close correlation between loss of protein expression and MMR-mRNA levels was found in highly microsatellite instable (MSI-H) tumours deficient of MLH1 or MSH2. MLH1/MSH2 ratio was low in 11 sporadic and nine hereditary MLH1-deficient carcinomas (mean 0.51), whereas the ratio was high in 17 MSH2-deficient hereditary non-polyposis colorectal cancer (HNPCC) associated carcinomas (mean 6.8). Notably, in the normal tissues of HNPCC patients with MSH2 mutations, the MLH1/MSH2 transcript ratios were significantly elevated (ratio > 2.0) as compared to the ratios of normal mucosa in patients with MMR-proficient tumours (27 of 32 ratio < 2.0; p = 0.00113). Analysis of B-lymphocytes of HNPCC patients with proven MMR gene mutation confirmed these findings. In conclusion, RT-PCR allows relative quantification of MMR gene mRNA expression in formalin-fixed and paraffin-embedded tissue. Furthermore, this approach enables quantification of haploinsufficiency due to nonsense-mediated mRNA decay in normal tissue and B-lymphocytes from patients carrying MSH2 germline mutations and may be useful for identification of asymptomatic carriers of pathogenic germline mutations.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/deficiência , Adenoma/metabolismo , Neoplasias Colorretais Hereditárias sem Polipose/metabolismo , Neoplasias Colorretais/metabolismo , Mutação em Linhagem Germinativa/genética , Proteína 2 Homóloga a MutS/deficiência , Proteínas Nucleares/deficiência , RNA Mensageiro/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Adenoma/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Linfócitos B/metabolismo , Estudos de Casos e Controles , Neoplasias Colorretais/genética , Neoplasias Colorretais Hereditárias sem Polipose/genética , Regulação Neoplásica da Expressão Gênica , Predisposição Genética para Doença/genética , Testes Genéticos , Humanos , Mucosa Intestinal/metabolismo , Pessoa de Meia-Idade , Proteína 1 Homóloga a MutL , Proteína 2 Homóloga a MutS/genética , Proteínas Nucleares/genética , RNA Mensageiro/genética , RNA Neoplásico/metabolismoRESUMO
CONTEXT: Patients with hyperplastic polyposis coli syndrome are thought to harbor precursor lesions of a proposed hyperplasia-carcinoma pathway in colorectal cancer, but morphologic recognition of such lesions remains difficult. Hypermethylation of the secreted Frizzled receptor protein 1 gene on chromosome 8p12 is one of the earliest molecular alterations in colorectal carcinogenesis, potentially disrupting the Wnt signaling cascade of cellular growth control. OBJECTIVE: To determine if hyperplastic polyps from patients with hyperplastic polyposis coli syndrome show a distinct immunohistochemical expression pattern for mismatch repair proteins and secreted Frizzled receptor protein 1 compared to their sporadic counterparts. DESIGN: Immunohistochemical studies (secreted Frizzled receptor protein 1, 3 mismatch repair proteins, and p53) were performed on 23 hyperplastic polyps, 6 synchronous colon cancers, and normal colonic mucosa from 6 patients with hyperplastic polyposis coli syndrome and were compared with studies of sporadic hyperplastic polyps obtained from 13 matched control subjects. RESULTS: The staining pattern for the mismatch repair proteins MLH-1, MSH-2, and MSH-6 did not differ between sporadic and syndromic hyperplastic polyps. In contrast, 52% of syndromic hyperplastic polyps showed a reproducible and distinct staining pattern for secreted Frizzled receptor protein 1 that was not seen in control specimens and that was associated with larger polyp size (P =.002) and location in the proximal colon (P =.01). CONCLUSIONS: Some hyperplastic polyps from patients with hyperplastic polyposis coli syndrome show a secreted Frizzled receptor protein 1 immunophenotype that could indicate alterations of cellular growth control. These findings may help identify precursor lesions in the proposed hyperplasia-carcinoma pathway of colorectal carcinogenesis.