Enolase is a glycolytic enzyme catalyzing the conversion of 2-phospho-d-glycerate to phosphoenolpyruvate. In mammals (including humans) there are three independent genetic loci, called ENO1, ENO3 and ENO2, encoding three isoforms of enolase, α, β and γ, respectively.(1,2) Isoform switching takes place along with terminal differentiation into neuronal and skeletal muscle cells from α-enolase to γ-and β-enolases, respectively. The γ isoform, known as neuron-specific enolase, is detected mainly in cells of neuronal origin and the β isoform is found mainly in adult skeletal muscle, whereas the α isoform is a major form of enolase present in the early stages of embryonic development, being expressed ubiquitously in different types of tissue.The ENO1 gene is located in chromosomal region 1p36.3-1p36.2. (4,5) This gene encodes an alternatively translated product, in addition to the ENO1 protein, by initiating translation at the Met-97 residue encoded in exon 5.(6) This product is identified as c-myc promoter binding protein 1 (MBP-1). MBP-1 does not have enzymatic enolase activity.(7) The 48-kDa form of ENO1 has enzymatic activity and is localized in the cytoplasm or in both cytoplasm and nuclei, whereas the shorter 37-kDa form (MBP-1) is preferentially localized in cell nuclei.(8) The two proteins are known to function as negative regulators for c-myc expression. (9) Recent findings have shown that α-enolase has several functions besides its innate glycolytic function, and plays an important role in several biological and pathophysiological processes. (10,11) In particular, α-enolase is considered to play potential roles in tumorigenesis. Tumor cells have a higher metabolic rate than surrounding normal tissues, and enolases are considered to be an important factor in cell metabolism. Several lines of evidence suggest that α-enolase may be involved in cancer invasion and metastasis.(12) Furthermore, an autoantigen of α-enolase was identified in non-small cell lung cancer and its overexpression was tightly correlated with poor survival outcomes. (13) Localization of α-enolase in rat oral epithelium by immunofluorescence microscopy has demonstrated the high level of α-enolase in oral epithelium, specifically in the cytoplasm of basal cells. (14) However, detailed observations of α-enolase localization in human oral epithelium and in oral squamous cell carcinoma (SCC) have not been undertaken thus far.In the present study, we investigated the localization of ENO1 gene transcripts detected as proteins with an immunohistochemical method and also as mRNA with an in situ hybridization method on tissue sections of oral epithelium and oral SCC, and demonstrated the differential distribution of the gene transcripts in normal and carcinoma cells.
Materials and MethodsTissue samples and histopathology. Ethical approval for this study was granted by the Institutional Review Board of Kawasaki Medical School, and written informed consent was obtained from all patients. Thirteen oral SCC of well differentiated type (five tongues, thre...
