Expression of B-cell translocation gene 2 protein in normal human tissues.

The antiproliferative B-cell translocation gene 2 (BTG2(TIS21/PC3)) is emerging as an important regulator of cell cycle dynamics. BTG2(TIS21/PC3) expression increases in response to the induction of DNA damage, cell differentiation, cell quiescence, cell contact, and as part of a positive feedback mechanism in response to growth stimulation. The objective of the present study was to provide further insight into the biological function of BTG2(TIS21/PC3) by determining the expression levels and cellular localization of BTG2(TIS21/PC3) in a spectrum of normal human tissues and to determine the proliferative indices (based on Ki-67 staining) and apoptotic indices (based on TUNEL assay) in those cell populations where BTG2(TIS21/PC3) was differentially expressed. Highest levels of BTG2(TIS21/PC3) expression were seen in kidney proximal tubules, lung alveolar bronchial epithelium and in the basal cell layer of prostate acini. BTG2(TIS21/PC3) was expressed at significantly different levels within the different epithelial populations of the kidney (proximal vs distal tubules) and prostate (acinar basal cells vs lumenal cells). Moderate levels of expression were seen in the acinar cells of breast and pancreas and in the mucosal epithelium of the intestine. Low levels of expression were seen in neurons, hepatocyctes, the zona granulosa of the ovary, round spermatids and thyroid follicles. Our results therefore indicate an imperfect correlation between the terminally differentiated phenotype and BTG2(TIS21/PC3) expression, but no correlation between basal cellular proliferative or apoptotic indices and BTG2(TIS21/PC3) expression levels.