Hudson D L, Sleeman J, Watt F M
Keratinocyte Laboratory, Imperial Cancer Research Fund, London, UK.
J Cell Sci. 1995 May;108 ( Pt 5):1959-70. doi: 10.1242/jcs.108.5.1959.
Although binding of peanut agglutinin (PNA) to keratinocytes is often used as a marker of terminal differentiation, the identity of the PNA-binding glycoproteins has been unclear. We now show that an antiserum raised against the glycoproteins recognises isoforms of CD44, the most abundant of which could be labelled with [35S]sulphate, indicating the presence of glycosaminoglycan side chains. RT-PCR analysis showed that keratinocytes expressed at least 5 forms of CD44 containing different numbers of exons from the variable region of the extracellular domain and also expressed the standard 'haemopoietic' form of CD44 which lacks the variable exons. Standard and variant isoforms of CD44 were expressed both by proliferating keratinocytes and cells undergoing terminal differentiation, although the level of CD44 mRNAs decreased when keratinocytes were placed in suspension to induce differentiation. The role of CD44 in intercellular adhesion was investigated by plating keratinocytes onto a rat pancreatic carcinoma line transfected with different CD44 isoforms. Keratinocyte adhesion to transfectants expressing variant exons 4-7 was greater than to cells expressing standard CD44 and could be inhibited with hyaluronan or digestion with hyaluronidase. These observations confirm earlier predictions that the PNA-binding glycoproteins of keratinocytes play a role in intercellular adhesion.
尽管花生凝集素（PNA）与角质形成细胞的结合常被用作终末分化的标志物，但PNA结合糖蛋白的身份一直不清楚。我们现在表明，针对这些糖蛋白产生的抗血清可识别CD44的异构体，其中最丰富的异构体可用[35S]硫酸盐标记，表明存在糖胺聚糖侧链。逆转录聚合酶链反应（RT-PCR）分析表明，角质形成细胞表达至少5种形式的CD44，其细胞外结构域可变区含有不同数量的外显子，并且还表达缺乏可变外显子的标准“造血”形式的CD44。CD44的标准和变异异构体在增殖的角质形成细胞和经历终末分化的细胞中均有表达，尽管当角质形成细胞置于悬浮液中诱导分化时，CD44 mRNA的水平会下降。通过将角质形成细胞接种到转染了不同CD44异构体的大鼠胰腺癌细胞系上来研究CD44在细胞间黏附中的作用。角质形成细胞与表达变异外显子4-7的转染细胞的黏附力大于与表达标准CD44的细胞的黏附力，并且可以被透明质酸或用透明质酸酶消化所抑制。这些观察结果证实了早期的预测，即角质形成细胞的PNA结合糖蛋白在细胞间黏附中起作用。
