Multiple complementary transcripts of pCMa1, a novel gene located at chromosome 11p15.1-2, and melanocytic cell transformation.

Abstract

The cDNA clone pCMa1 (0.45 kb) is one of the 12 novel cDNAs, previously identified when comparing RNA expression profiles of melanocytes, naevus cells, and non-metastatic melanoma cells. This clone did not reveal a unique long open reading frame. The pCMa1 gene localized to the distal, telomere proximal region on the short arm of chromosome 11.p15.1-2. Northern blot analyses with single-stranded cRNA probes revealed the presence of various complementary pCMa1 transcripts of different lengths, which are not enriched in the poly(A)(+) RNA fraction. The arbitrarily defined plus strand (used as a probe) mainly hybridized to 0.45 kb and 4.0 kb minus transcripts in total RNA samples, and the minus strand (used as a probe) hybridized to a major plus transcript of 4.0 kb. By RNA in situ hybridization, the highest levels of the plus transcripts were observed in melanocytic naevi (12/12), particularly in congenital naevi, whereas normal skin melanocytes (12/12) were negative. pCMa1 plus transcripts were detected in naevus cell nests (100%) near the dermo-epidermal junction. Expression, however, diminished to some extent in the deeper parts of the melanocytic naevi. Although most of the cutaneous primary melanoma lesions (11/15) showed detectable, but variable levels of plus transcripts of pCMa1 in the papillary to reticular dermis, not more than 10% of the melanoma cells were positive. The majority of melanoma metastases (6/7) were negative, while the positive lesion originated from a patient with a positive primary melanoma. Furthermore, plus transcripts were present in the nuclei of non-metastatic melanoma cells in culture, whereas metastatic cells showed elevated expression both in the nucleus and in the cytoplasm. Briefly, the data show transient up-regulation of pCMa1 in neoplastic progression of melanocytic cells, with peak levels occurring during naevus stages, and suggest that pCMa1 is a molecular marker in melanocytes for the early changes from the proliferating phenotype to malignant transformation.