RESUMO
Bone morphogenic proteins (BMPs) are members of the TGFB growth factor superfamily with well-described functions in bone formation. Although disrupted BMP signalling in tumor development has more recently been investigated, a role for BMP3 in colorectal cancer (CRC) has remained largely unexplored. The aim of this study was to investigate BMP3 disruption in CRCs in relation to both the traditional and serrated pathways of tumor progression. BMP3 was down-regulated as assessed by real-time PCR in 50 of 56 primary tumors (89%). Bisulfite sequencing of the putative promoter revealed extensive hypermethylation in the cell line HT29, in which expression could be restored by treatment with a methyltransferase inhibitor. Aberrant hypermethylation was observed in 33/60 (55%) tumors and was highly correlated with microsatellite instability (P < 0.01), the CpG Island Methylator Phenotype (P < 0.01), BRAF oncogene mutation (P < 0.01), and proximal location (P < 0.001). Methylation was also frequently observed in serrated and traditional adenomatous polyps (22/29, 76%). Re-introduction of BMP3 into cell lines revealed marked growth suppression supporting the functional relevance of this alteration in colorectal tumor development. This study provides molecular and functional data supporting the importance of BMP3 silencing as an early and frequent event in colorectal tumors progressing via the serrated and traditional pathways.
Assuntos
Adenocarcinoma/genética , Proteínas Morfogenéticas Ósseas/fisiologia , Transformação Celular Neoplásica/genética , Neoplasias Colorretais/genética , Metilação de DNA , Genes Supressores de Tumor , Proteínas Adaptadoras de Transdução de Sinal/genética , Adenocarcinoma/metabolismo , Adenoma/genética , Adenoma/metabolismo , Proteína Morfogenética Óssea 3 , Linhagem Celular Tumoral , Estudos de Coortes , Pólipos do Colo/genética , Pólipos do Colo/metabolismo , Neoplasias Colorretais/metabolismo , Neoplasias Colorretais Hereditárias sem Polipose/genética , Neoplasias Colorretais Hereditárias sem Polipose/metabolismo , Ilhas de CpG , Progressão da Doença , Humanos , Mucosa Intestinal/metabolismo , Perda de Heterozigosidade , Instabilidade de Microssatélites , Proteína 1 Homóloga a MutL , Proteínas Nucleares/genética , Lesões Pré-Cancerosas/genética , Lesões Pré-Cancerosas/metabolismo , Regiões Promotoras Genéticas/genética , Técnica de Subtração , Ensaio Tumoral de Célula-TroncoRESUMO
BACKGROUND: SnoN is an important regulator of the transforming growth factor beta (TGFbeta) signalling pathway and has been shown to exhibit both tumour promotion and suppression activity. METHODS: To further explore the role of this complex molecule in colorectal tumorigenesis, we examined 52 paired normal and tumour colorectal specimens stratified by level of microsatellite instability; 18 with high-level microsatellite instability (MSI-H) and 34 microsatellite stable (MSS). SnoN transcript expression was quantitated by real-time PCR and analysed with respect to clinical indicators of prognosis. RESULTS: Within the MSI-H subgroup, SnoN was commonly either up-regulated (6/18, 33%) or down-regulated (7/18, 39%). A significantly different distribution of SnoN expression was observed in MSS cancers compared with MSI-H (P < or = 0.001). Whilst 17/34 (50%) of MSS tumours demonstrated up-regulation, none showed down-regulated expression. Within the MSI-H subgroup, up-regulation was significantly correlated with lack of repeat tract mutation in the TGFbetaRII gene (P < or = 0.025), suggesting that SnoN is more frequently up-regulated in the presence of functional TGFbeta signalling. CONCLUSION: Together these data support the notion that SnoN has both oncogenic and tumour suppressive properties depending on other genetic changes within the tumour, and that the MSI-H pathway of colorectal tumorigenesis presents an excellent model for the study of these opposing functions.