Epigenetic silencing contributes to frequent loss of the fragile histidine triad tumour suppressor in basal cell carcinomas

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Abstract
Extensive exposure to ultraviolet radiation is associated with genetic alterations in basal cell carcinomas (BCCs), which represent some 75% of skin cancers. As recent data suggested the fragile histidine triad (FHIT) gene product to participate in DNA damage responses we wished to address whether functional deletion of this tumour suppressor participates in the development of BCC. Our study focused on epigenetic inactivation of the FHIT gene. Paraffin-embedded specimens from 17 patients with BCC were available for methylation-specific polymerase chain reaction (MSP), combined bisulphite-dependent restriction analysis (COBRA) of the FHIT gene and immunohistochemistry of its product. We report for the first time that 100% of BCCs are negative for FHIT by immunostaining. Aberrant methylation of the FHIT promoter occurred in a significant portion of BCCs. MSP detected hypermethylation of the FHIT/FRA3B locus in nine of nine (100%) periocular BCCs and in six of eight (75%) BCCs from other body regions. COBRA yielded similar results, confirming that some 88% of the 17 BCCs analysed harbour epigenetic silencing of the FHIT gene. Loss of FHIT protein was demonstrated immunohistochemically, confirming that promoter hypermethylation correlated with loss of gene expression. We have identified epigenetic silencing of the FHIT tumour suppressor gene as a frequent inactivation mechanism which is likely to contribute to functional deficiencies in DNA damage response of BCCs.

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