Kam E, Nirunsuksiri W, Hager B, Fleckman P, Dale B A
Department of Oral Biology, University of Washington, Seattle 98195-7132, USA.
Br J Dermatol. 1997 Dec;137(6):874-82.
We investigated serine/threonine protein phosphatase (PP) activity and the expression of PP2A during growth and differentiation of epidermal keratinocytes in culture. Keratinocyte PP activity was strongly inhibited by calyculin A and okadaic acid, indicating that the activity was mainly due to PP2A and PP1. The phosphatase activity decreased to about 20% of the initial (day 1) level by the time of confluence and to about 10% at day 7 postconfluence. In contrast to activity, the level of expression of the PP2A catalytic subunit protein and the mRNA for the two isoforms increased slightly over the period of growth. Keratinocyte differentiation was shown by a significant increase in profilaggrin expression after confluence. Keratinocytes were also cultured from individuals affected with harlequin ichthyosis. This severe hyperkeratotic skin disorder has abnormal lipid structures and is blocked in the PP2A-dependent conversion of phosphorylated profilggrin to the non-phosphorylated filaggrin. The PP activity in harlequin cultures was lower than in normal cultures (about 20% of the subconfluent normal control value) and decreased even further in confluent cultures. In contrast, the level of expression of the PP2A catalytic subunit protein and mRNA for the two isoforms was similar to that of normal keratinocytes and increased with confluence. These results suggest that PP activity in keratinocytes is regulated in a post-translational manner; they also support the possibility of impaired or reduced function of PPs in harlequin ichthyosis.
我们研究了培养的表皮角质形成细胞生长和分化过程中丝氨酸/苏氨酸蛋白磷酸酶（PP）的活性以及PP2A的表达。角质形成细胞的PP活性受到花萼海绵诱癌素A和冈田酸的强烈抑制，这表明该活性主要归因于PP2A和PP1。到汇合时，磷酸酶活性降至初始（第1天）水平的约20%，汇合后第7天降至约10%。与活性相反，在生长期间，PP2A催化亚基蛋白的表达水平以及两种同工型的mRNA略有增加。汇合后聚丝蛋白原表达显著增加表明角质形成细胞发生了分化。我们还从丑角样鱼鳞病患者中培养了角质形成细胞。这种严重的角化过度性皮肤病具有异常的脂质结构，并且在PP2A依赖的磷酸化聚丝蛋白原向非磷酸化丝聚蛋白的转化过程中受阻。丑角样鱼鳞病培养物中的PP活性低于正常培养物（约为亚汇合正常对照值的20%），并且在汇合培养物中进一步降低。相比之下，PP2A催化亚基蛋白和两种同工型mRNA的表达水平与正常角质形成细胞相似，并随着汇合而增加。这些结果表明角质形成细胞中的PP活性是以翻译后方式调节的；它们还支持了丑角样鱼鳞病中PP功能受损或降低的可能性。
