Melanoma-inhibiting activity/cartilage-derived
retinoic acid-sensitive
protein, a 11 kDa
protein, is mainly expressed in cartilage during embryogenesis, and is related to invasion,
metastasis, and
immunomodulation of
melanoma and
glioma cells in vivo and in vitro. Here, we describe an alternative splice product of this gene termed
melanoma-inhibiting activity (splice), lacking exon 2 of the original
protein. A predicted frameshift by alternate splicing results in a unique C-terminal portion of the
protein. Consistent with this, a
protein migrating at the predicted molecular weight of the splice form (3.5 kDa) was detected using an N-terminal specific antibody. This band was undetectable when using a C-terminal specific antibody. In addition, we describe the expression pattern of
melanoma-inhibiting activity (splice) in different human
tumors. Expression was shown in tissue samples of five of six primary
melanomas, 11 of 12 primary sites of metastatic
melanomas, 10 of 10 systemic
metastases of
melanomas, four of four central nervous system
metastases of
melanomas, six of eight primary
melanoma cultures, and five of five
melanoma cell lines. Only a faint signal was obtained in tissue samples of five of six naevi. Interestingly, seven of eight nonmelanocytic tissue samples and five of seven
glioma cell lines showed weak expression of
melanoma-inhibiting activity (splice). Approaching first functional aspects,
reverse transcriptase-polymerase chain reaction showed weak expression of
melanoma-inhibiting activity (splice) in relation to
melanoma-inhibiting activity in nonmelanocytic and strong expression in melanocytic cells. Staining with a specific anti-serum raised against a synthetic
peptide resembling the amino acid sequence of
melanoma-inhibiting activity (splice) showed a more nuclear staining pattern in comparison with
melanoma-inhibiting activity. Furthermore, incubation of
melanoma and
glioma cell cultures with transforming growth factor-beta2 showed inverse regulation of the
mRNA of
melanoma-inhibiting activity and
melanoma-inhibiting activity (splice), both suggesting also a different function within the physiologic role of this unique family of
proteins.
Melanoma-inhibiting activity (splice) has no homology to any other known
protein so far. Whereas the biologic function of
melanoma-inhibiting activity (splice) is not clear yet, it might provide a relevant diagnostic and therapeutic tool for
malignant melanomas.