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末期，但分化末期与细胞凋亡之间的确切关系尚不清楚。在目前的研究中，bcl-2原癌基因是一种已知的细胞凋亡抑制剂；在正常人的层状鳞状上皮中，其表达仅限于基底细胞层。Bcl-xL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。在培养的角化细胞中，Bcl-xL在0.1 mM钙（低Ca2+）条件下表达，但在1.0 mM钙（高Ca2+）条件下消失；后者诱导角质细胞分化。Bax在低Ca2+的角质形成细胞中不表达，但在高Ca2+的细胞中表达。最后，高Ca2+的角化细胞凋亡，通过TUNEL法和180 bp DNA片段检测。为了研究bcl-2蛋白在口腔角质形成细胞分化过程中的功能作用，我们将bcl-2表达载体转染到SCC-25细胞中，SCC-25细胞在体外正常进行鳞状细胞分化，同时表达特异性分化标志物，如角质蛋白10/11和天花素。在bcl-2转染的SCC-25细胞中，这些分化标志物的表达明显受到抑制。bcl-2原癌基因可能在反对口腔角化细胞向终末分化和凋亡的承诺中起关键作用。提示牙龈上皮终末分化过程是细胞凋亡的一个途径。

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.