The tumor suppressor gene 14-3-3 sigma is commonly methylated in normal and malignant lymphoid cells

14-3-3 sigma/Stratifin was first identified as an epithelial cell antigen (HME-1) exclusively expressed in epithelia. However, the functional role of sigma in cell proliferation and apoptosis would suggest that this protein could be relevant to the regulation of growth and differentiation of multiple cell types. Recent evidence demonstrates that sigma acts as a tumor suppressor gene that is inactivated by methylation of its 5' CpG islands in epithelial tumor cells. In normal epithelia, sigma is commonly unmethylated. The objective of this study was to determine the methylation status of sigma in lymphoid cells. We now demonstrate by methylation-specific PCR analysis that sigma is also methylated in normal and malignant lymphocytes. Such methylation, however, fails to completely silence its expression. Compared with the robust expression in epithelial cells, lymphocytes showed basal, but clearly evident, levels of sigma as determined by reverse transcription-PCR and Western blot. The finding of sigma 5' region methylation in lymphocytes has direct implications in the use of body fluids on methylation tests for noninvasive monitoring of occult epithelial tumor cells and suggests that sigma may not be an adequate biomarker for methylation-specific PCR analysis.