Growth and differentiation of keratinocytes : Molecular and histological study

口腔角质形成细胞起源于基底细胞，在迁移到表面的过程中分化，最后脱落。细胞凋亡发生在分化的末期，但终末分化与细胞凋亡之间的确切关系尚不清楚。在本研究中，bcl2原癌基因是已知的细胞凋亡抑制因子；在正常人类复层鳞状上皮中，其表达仅限于基底细胞层。Bclxl表达于基底细胞层和棘细胞层，bax表达于棘细胞层和颗粒细胞层。在培养的角质形成细胞中，在0.1 mM钙离子(低钙)条件下表达，而在1.0 mM钙离子(高钙离子)条件下表达消失，后者诱导角质形成细胞分化。Bax在低钙的角质形成细胞中不表达，在高钙的角质形成细胞中表达。用原位末端标记法和180bp DNA片段法检测高钙的角质形成细胞发生凋亡。为探讨bcl2蛋白在口腔角质形成细胞分化过程中的作用，将bcl2表达载体导入体外正常分化的SCC-25细胞，同时表达角蛋白10/11和外套蛋白等特异性分化标记物。在bcl2基因转染的SCC-25细胞中，这些分化标志物的表达受到明显抑制，bcl2原癌基因可能在对抗口腔角质形成细胞终末分化和凋亡的过程中发挥关键作用。这些结果表明，牙龈上皮细胞的终末分化过程是一条诱导细胞凋亡的途径。

Oral keratinocytes originate from basal cells, differentiate during migration to the surface, and finally are shed. Apoptosis occurs at the end of differentiation, but the precise relationship between terminal differentiation and apoptosis is not clear. In the present study, The bcl-2 proto-oncogene is a known inhibitor of apoptosis ; in normal human stratified squamous epithelium its expression is restricted to the basal cell layr. Bcl-xL was expressed in the basal cell and spinous cell layrs, and Bax was expressed in the spinous cell and granular cell layrs. In cultured keratinocytes, Bcl-xL was expressed under conditions of 0.1 mM calcium (low Ca2+) but disappeared under conditions of 1.0 mM calcium (high Ca2+) ; the latter induces keratinocyte differentiation. Bax was not expressed in keratinocytes with low Ca2+ but was expressed in cells with high Ca2+. And finally keratinocytes with high Ca2+ underwent apoptosis, which was detected by the TUNEL method and by 180-bp DNA fragmentation. To investigate the functional role of bcl-2 protein in the process of differentiation of oral keratinocytes, bcl-2 expression vector was transfected into SCC-25 cells, which normally undergo squamous cell differentiation in vitro while expressing specific differentiation markers, e.g., keratin10/11 and involucrin. In bcl-2 transfected SCC-25 cells, the expression of these differentiation markers was markedly suppressed.The bcl-2 proto-oncogene may play a critical role in opposing the commitment to terminal differentiation and apoptosis of oral keratinocytes. These results suggest that the process of terminal differentiation in gingival epithelium is a pathway to apoptosis.