The CD44 receptor of the mouse LB T-cell lymphoma: analysis of the isoform repertoire and ligand binding properties by reverse-transcriptase polymerase chain reaction and antisense oligonucleotides.

CD44 is a cell surface glycoprotein involved in cell migration and cell docking in target organs via interactions with various ligands, including hyaluronic acid (HA), which is the principal ligand of this receptor. Alternative splicing generates many isoforms of CD44, including standard CD44 (CD44s) and CD44 variants (CD44v). LB T-cell lymphoma, which predominantly expresses CD44s, acquires additional CD44v and HA binding capacity after activation with phorbol ester. The HA9 cell line, isolated from parental LB cells, expresses CD44v and constitutively binds HA. Downregulation of CD44v isoforms of HA9 cells, by CD44v specific antisense inhibited their ability to bind HA, indicating that CD44v, rather than CD44s, is associated with the activation status of this molecule. Using the reverse transcriptase polymerase chain reaction, we found that LB cells after infiltrating spleen and lymph nodes of BALB/c mice, contain an enriched repertoire of CD44v, implying that the metastatic cells acquired the activated form of this receptor.