CD44 VARIANT ISOFORMS ARE PREFERENTIALLY EXPRESSED IN BASAL EPITHELIAOF NONMALIGNANT HUMAN FETAL AND ADULT TISSUES

CD44 is a transmembrane glycoprotein, which can exist in a multitude o f isoforms due to alternative splicing of the pre-mRNA. We have genera ted monoclonal antibodies to several of these variant regions, which a re encoded by 10 additional exons in the extracellular part of the mol ecule. CD44 variant isoforms have been reported to be involved in the malignant progression of rat and human tumours. The precise localizati on of CD44 variant isoforms in normal developmental and morphogenetic processes is essential for diagnostic studies of human tumorigenesis. Therefore, we have analysed a large number of different human tissues by immunohistochemistry for the expression of CD44 isoforms containing either exons 4v, 6v or 9v. Expression of exon 9v-isoforms was detecte d in almost all epithelia analysed, with a few exceptions. Exon 6v iso forms are expressed only in squamous and glandular epithelia, e.g. ski n epidermis, sweat and sebaceous glands, oesophagus, ducts of the mamm ary gland, salivary and prostate glands. Detection of exon 4v-encoded isoforms was restricted to the epidermis and the oesophagus. Similar t issue distributions of CD44 variant isoforms were observed in 10-week- old fetal tissues. Since one of the ligands of CD44 is hyaluronic acid (HA), we also analysed the tissue distribution of HA synthetase. HA s ynthetase was detected in all tissues analysed, showing good correlati on with the expression of the standard form of CD44, CD44s.