Marvin K W, George M D, Fujimoto W, Saunders N A, Bernacki S H, Jetten A M
Cell Biology Section, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709.
Proc Natl Acad Sci U S A. 1992 Nov 15;89(22):11026-30. doi: 10.1073/pnas.89.22.11026.
In this study, we have characterized the cDNA clone SQ37 that was isolated previously from a rabbit squamous cell library. The gene encodes a 14-kDa protein that appears to function as a component of the cross-linked envelope in squamous differentiating cells. The protein, which has been named cornifin, has a high content of proline (31%), glutamine (20%), and cysteine (11%) and contains 13 repeats of an octapeptide (consensus sequence, EPCQPKVP) at its C terminus. SQ37 mRNA and protein are induced during squamous differentiation of rabbit tracheal (RbTE) cells and human epidermal keratinocytes. This induction is repressed by retinoids. Immunohistochemical studies reveal SQ37 immunoreactivity in fragmented cross-linked envelopes from squamous-differentiated RbTE cells and in the suprabasal layers of the epidermis. In situ hybridization analysis showed that the presence of SQ37 mRNA is restricted to the suprabasal layers. Treatment of RbTE cells with a Ca2+ ionophore induces cross-linking of the SQ37 protein into higher molecular weight complexes. This cross-linking reaction appears to be mediated by transglutaminase type I. Our observations suggest that the protein encoded by SQ37 participates in the assembly of the cross-linked envelope.
在本研究中，我们对先前从兔鳞状细胞文库中分离得到的cDNA克隆SQ37进行了表征。该基因编码一种14 kDa的蛋白质，它似乎作为鳞状分化细胞中交联包膜的一个组分发挥作用。这种已被命名为角质化包膜蛋白的蛋白质含有高含量的脯氨酸（31%）、谷氨酰胺（20%）和半胱氨酸（11%），并且在其C末端含有13个八肽重复序列（共有序列，EPCQPKVP）。SQ37 mRNA和蛋白质在兔气管（RbTE）细胞和人表皮角质形成细胞的鳞状分化过程中被诱导表达。这种诱导作用被视黄酸抑制。免疫组织化学研究显示，在鳞状分化的RbTE细胞的破碎交联包膜以及表皮的基底层上方各层中存在SQ37免疫反应性。原位杂交分析表明，SQ37 mRNA的存在仅限于基底层上方各层。用钙离子载体处理RbTE细胞会诱导SQ37蛋白质交联形成更高分子量的复合物。这种交联反应似乎是由I型转谷氨酰胺酶介导的。我们的观察结果表明，SQ37编码的蛋白质参与交联包膜的组装。
