Transcripts encoding mouse CD44 (Pgp‐1, Ly‐24) antigen: strain variation and induction by mitogen

The cell surface molecule CD44, thought to be a cell surface receptor for hyaluronic acid, is expressed by thymocytes and peripheral T cells. Following T cell activation with mitogens or antigens, surface expression of CD44 increases. This increase in CD44 cell surface expression has been used as a means of identifying memory T cells in vivo. In this report, using Northern analysis, we have quantitated mouse CD44 transcripts in thymocytes and a cloned T hybridoma cell line. In contrast to a recent report by Nottenburg et al. (Proc. Natl. Acad. Sci. USA 1989. 86: 8521), we show that in all instances CD44 transcripts are polyadenylated. In all cells studied, three major mRNA species of approximately 4.5, 3.5 and 1.6 kb are detected. After stimulation with phorbol 12‐myristate 13‐acetate (PMA), there is a de novo protein synthesis‐dependent increase in the level of CD44 transcripts. The increase in CD44 transcripts precedes the increase in cell surface expression. In contrast to CD44, PMA stimulation results in a decrease in the level of Thy‐1 transcripts. Thymocytes from different mouse strains vary in their level of CD44 cell surface expression and Northern analysis indicates that this mouse strain variation correlates with a corresponding difference in the level of CD44 transcripts.