Risek B, Pozzi A, Gilula N B
Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
J Cell Sci. 1998 May;111 ( Pt 10):1395-404. doi: 10.1242/jcs.111.10.1395.
Retinoids and phorbol esters have profound effects on proliferation and differentiation of epidermal keratinocytes when applied topically on rodent skin. Since both agents also modulate gap junction (GJ)-mediated cell-cell communication, we have examined the effects of all-trans retinoic acid (RA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) on the expression of alpha1 (Cx43) and beta2 (Cx26) connexins, the two major gap junction gene products in mature rat epidermis. In fully differentiated, mature epidermis, alpha1 is expressed in the lower, less differentiated portion, while beta2 is localized in upper, more differentiated layers. Dorsal skin of 21-day old rats was treated topically with a single dose of RA, TPA or vehicle alone and used for histological and molecular analyses at different time points. Keratinocytes in interfollicular epidermis were examined for proliferation and differentiation using specific antibodies for keratins (K10, K14) and proliferating cell nuclear antigen (PCNA). An increase in epidermal thickness was noticed within 4 hours after the application of RA or TPA. This increase, however, appeared to be primarily due to hypertrophy, since no substantial changes were observed in the proliferative index of epidermal keratinocytes. PCNA immunoreactivity significantly increased after 8 hours treatment of RA or TPA, suggesting a hyperproliferative growth response. Epidermal hyperplasia was confirmed by monitoring the expression patterns of K10 and K14 in RA- or TPA-treated skin. RA-induced hyperplasia lasted longer as compared to TPA induction. Changes in keratin phenotypes were paralleled by an increase in alpha1 and beta2 connexin expression as well as their colocalization in same epidermal layers. Differences in hyperplastic growth response kinetics were also confirmed at the connexin level, with beta2 antigen sustained for longer and at higher levels in suprabasal layers of RA-treated skin. Overall, this type of connexin expression resembled that observed in the non-differentiated rat epidermis during embryonic development. An increase in alpha1 and beta2 connexin abundance was also observed at the protein and RNA levels. At 96 hours after RA or TPA treatment, expression of both connexins was similar to that of the control epidermis. Taken together, these findings suggest that a higher level of GJ-mediated cell-cell communication, is required for the maintenance of homeostasis during periods of rapid epidermal growth and differentiation.
视黄酸和佛波酯局部应用于啮齿动物皮肤时，对表皮角质形成细胞的增殖和分化有深远影响。由于这两种物质也调节间隙连接（GJ）介导的细胞间通讯，我们研究了全反式维甲酸（RA）和12-O-十四烷酰佛波醇-13-乙酸酯（TPA）对α1（Cx43）和β2（Cx26）连接蛋白表达的影响，这两种蛋白是成熟大鼠表皮中两种主要的间隙连接基因产物。在完全分化的成熟表皮中，α1在较低、分化程度较低的部分表达，而β2定位于上部、分化程度较高的层。对21日龄大鼠的背部皮肤局部给予单剂量的RA、TPA或单独使用赋形剂，并在不同时间点进行组织学和分子分析。使用针对角蛋白（K10、K14）和增殖细胞核抗原（PCNA）的特异性抗体，检测毛囊间表皮中的角质形成细胞的增殖和分化情况。在应用RA或TPA后4小时内，观察到表皮厚度增加。然而，这种增加似乎主要是由于肥大，因为在表皮角质形成细胞的增殖指数中未观察到实质性变化。在RA或TPA处理8小时后，PCNA免疫反应性显著增加，表明有过度增殖性生长反应。通过监测RA或TPA处理皮肤中K10和K14的表达模式，证实了表皮增生。与TPA诱导相比，RA诱导的增生持续时间更长。角蛋白表型的变化与α1和β2连接蛋白表达的增加及其在同一表皮层中的共定位平行。在连接蛋白水平也证实了增生性生长反应动力学的差异，在RA处理皮肤的基底层以上，β2抗原持续时间更长且水平更高。总体而言，这种类型的连接蛋白表达类似于胚胎发育期间在未分化大鼠表皮中观察到的情况。在蛋白质和RNA水平上也观察到α1和β2连接蛋白丰度的增加。在RA或TPA处理96小时后，两种连接蛋白的表达与对照表皮相似。综上所述，这些发现表明，在表皮快速生长和分化期间，维持体内平衡需要更高水平的GJ介导的细胞间通讯。
