Expression of the transmembrane glycoprotein CD44 and metastasis associated 18A2/MTS1 gene in B16 murine melanoma cells.

CD44 is a transmembrane cell adhesion-mediating protein which occurs as alternatively spliced isoforms in a variety of cell types. CD44 isoforms have been reported to be differentially expressed in cancers and the isoform CD44v6 has often been associated with metastatic potential. The 18A2/mts1 gene, which codes for a Ca(2+)-binding protein of the S-100 family, is a metastasis associated gene and its expression has been shown to be related to cell proliferation, cancer metastasis and invasion. The association of 18A2/mts1 expression with invasion has been attributed to its ability to promote depolymerisation of cytoskeletal elements and it appears to also participate in the remodelling of the extracellular matrix. Here we have examined the expression of CD44v6 in metastatic variants of the B16 melanoma with different levels of 18A2/mts1 expression. We found that metastatic potential was not related to the overall CD44 expression as detected by immunostaining; the high metastasis variant ML8 showed reduced CD44v6 positivity as compared with the low metastasis variant F1. Up-regulation of 18A2/mts1 expression in F1 cells by a-melanocyte stimulating hormone (MSH) and its down-regulation in ML8 cells by RA reduced the numbers of CD44v6 staining cells. In F1 cells the glycoprotein was found to be uniformly associated with the cell membrane. But in F1 cells treated with a-MSH where 18A2/mts1 expression was up-regulated, CD44v6 showed redistribution into a patchy focal pattern. This patchy focal distribution of CD44v6 also occurred in ML8 cells which express 18A2/mts1 at a high level. It is suggested that the patching of CD44v6 molecules is a consequence of the changes in cytoskeletal dynamics brought about by 18A2/mts1 expression, that are conducive to aggregation and patching of these transmembrane glycoproteins. It is postulated that this induction of patching could provide discrete and strong adhesive foci promoting cell adhesion and invasive behaviour.