Immunohistochemical characterization of FHIT expression in normal human tissues

Fragile histidine triad is a tumor suppressor gene that is commonly inactivated in human tumors. Interestingly, the normal pattern of FHIT expression is largely unknown. This study is aimed to characterize the expression of FHIT protein in normal human tissues. A total of 119 normal human tissue specimens were analyzed for the FHIT expression using immunohistochemistry technique. The inclusion criteria included: normal/inflammatory tissue with no evidence of cellular atypia. All studied specimens were stained positively with FHIT and showed either nuclear or cytoplasmic expression. Interestingly, the pattern of FHIT staining was similar among different specimens from each organ. FHIT is located predominantly in the nucleus, although cytoplasmic staining is also present in some cell types. Oral squamous epithelium, breast ductal epithelium, squamous and tubal metaplastic epithelium of the uterine cervix, esophageal squamous epithelium, salivary glands, and bronchial epithelia all strongly expressed the nuclear protein. In connective tissue, FHIT has shown strong cytoplasmic expression in histocytes including macrophages and dendritic cells, fibroblasts, and myofibroblasts. Documentation of the pattern of FHIT expression in normal tissues will contribute to our understanding of the normal function of this protein and to interpretation of potentially altered FHIT expression in human tumors.