EXPRESSION OF CD44 ISOFORMS CARRYING METASTASIS-ASSOCIATED SEQUENCES IN NEWBORN AND ADULT-RATS

Expression of a splice variant of CD44, recognised by the monoclonal a ntibody (Mab) 1.1ASML, confers metastatic potential to non-metastasisi ng tumour cells (Cell 1991, 65, 13-24). To explore whether the metasta sis-associated variant of CD44 (CD44v) is expressed under physiologica l conditions, tissues of newborn and adult rats were stained with the Mab 1.1ASML. The 1.1ASML epitope is, indeed, expressed on the basal la yer of the epidermis and the hair follicles as well as on cryptic epit helia in the gut. In addition, ductal epithelia of the pancreatic glan d of newborn rats express CD44v. This pattern of expression differs fr om that of standard lymphocyte CD44 (CD44s). The anti-CD44s mAB Ox50 p redominantly stains connective tissue. Although different variants of CD44 may express the epitope recognised by 1.1ASML, cells expressing C D44v share properties with metastasising tumour cells: the stage of pr oliferation and a restricted degree of mobility. Thus, during metastat ic progression tumour cells may reactivate the expression of gene segm ents which serve highly specialised functions in embryonic and adult t issues.