EXPRESSION AND FUNCTION OF THE CD44 GLYCOPROTEIN IN MELANOMA CELL-LINES

We have analysed a panel of murine and human melanoma cell lines for e xpression of the glycoprotein CD44. All 12 cell lines examined express ed CD44 at their cell surfaces, as demonstrated by fluorocytometric an alysis using monoclonal antibodies (MAbs) IM7 and F10.44.2. Northern a nalysis revealed three transcript sizes that were 4.5, 2.2, and 1.5 kb in the human cell lines and 4.5, 3.0, and 1.5 kb in the murine cell l ines. Levels of mRNA did not correlate with level of surface expressio n, which was highly variable between the cell lines. RT-PCR analysis o f mRNA revealed that the major band identified was the expected 792 bp fragment indicative of the CD44H haemopoietic form, compared to a 119 4 bp form found in the human colorectal adenocarcinoma cell line HT29, indicative of the CD44E epithelial form. There was no evidence of var iant CD44 mRNA in our panel of melanomas. Functional assays revealed n o clear correlation between the level of cell surface CD44 and the abi lity of the melanoma cell lines to adhere to hyaluronate. Rather adher ence appeared to relate to the activation status of CD44 on the differ ent cell lines as a consequence of MAb stimulation (e.g. the 1735P lin e demonstrated a 46.2 +/- 5.7% adherence in an inactivated state versu s 62.4 +/- 5.6% adherence in an activated state to 5 mg/ml hyaluronate ) and suggests that the functional capacity of CD44 expressed by melan oma cells may be modified more by activation state than by RNA splicin g.