REGULATION OF HUMAN CD44H AND CD44E ISOFORM BINDING TO HYALURONAN BY PHORBOL-MYRISTATE ACETATE AND ANTI-CD44 MONOCLONAL AND POLYCLONAL ANTIBODIES

CD44 molecules are comprised of multiple alternatively spliced forms a nd are associated with diverse functions such as mediation of carcinom a metastasis and T cell coactivation. To study the function of individ ual CD44 isoforms, we have transfected CD44 isoforms into CD44-negativ e Jurkat T cells and produced cloned Jurkat cell lines that are stably transfected with either a CD44 isoform containing no alternatively sp liced insert (CD44H) or a CD44 variant (CD44E) containing an insert of 132 amino acids derived from exons 12, 13, and 14 of the CD44 gene. W e found that neither CD44H- nor CD44E-transfected Jurkat T cells const itutively bound hyaluronan (HA), whereas PMA treatment induced Jurkat cells transfected with CD44H but not CD44E to bind HA. CD44 mAb agains t noninsert regions of the CD44 extracellular domain (A3D8, A1G3) and polyclonal antisera against the COOH-terminal extracellular glycosamin oglycan region of CD44H (anti-6A serum) both induced CD44H-transfected cells to bind HA, whereas only one CD44 mAb (A1G3) induced CD44E-tran sfected Jurkat T cells to bind HA. Studies of Jurkat cells transfected with CD44H forms with truncations of the CD44 cytoplasmic domain demo nstrated that the cytoplasmic COOH-terminal 52 amino acids were critic al for binding of HA to the CD44 extracellular domain. Thus, these dat a underscore the importance of the CD44 cytoplasmic domain in the func tion of the extracellular portion of CD44H, and demonstrate a role for ligation of human CD44 isoforms at multiple distinct sites in regulat ion of expression of CD44 binding to HA. Journal of Immunology, 1993, 151: 6490.