Carcinogenesis, Vol. 23, No. 11, 1821-1830,
November 2002
© 2002 Oxford University Press
CANCER BIOLOGY |
Human melanomas of fibroblast and epithelial morphology differ widely in their ability to synthesize retinyl esters
Laboratory of Cellular Carcinogenesis and Tumor Promotion, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892-4255, USA
Reduced retinyl ester synthesis has been associated with several forms of cancer; we therefore proposed studying melanoma development from the perspective of this biochemical pathway. Cultures of human melanoma cells with fibroblastoid morphology showed negligible retinyl ester synthesis; in sharp contrast, those with epithelioid morphology were capable of retinol esterification. Further, isolated proliferating epidermal melanocytes (HFSC/2) esterified retinol, whereas proliferating normal skin fibroblasts (F:CCD-1121.Sk) did not. A primary site cutaneous melanoma and its metastatic match (both of epithelioid morphology) were capable of retinol esterification, while a matched fibroblastoid tumor pair did not synthesize retinyl esters; nevertheless, LRAT (lecithin:retinol acyltransferase) protein was found in microsomal fractions from all four tumors. A mutation screen in the LRAT coding region and adjacent intronic sequences revealed several novel mutations in these melanomas as well as in HFSC/2 and F:CCD-1121.Sk cells: a single nucleotide polymorphism in exon 1(37A
G), a silent mutation in exon 2a (188 AG/186 GA), and an insertion in the 5'UTR (9–10insC). CRBP-1 basal expression was present in the HFSC/2, and in both sets of matched tumor pairs; however, steady-state levels in the fibroblastoid melanoma pair were one-third that found in the epithelioid matched tumor pair. Co-culture of human primary site epithelioid melanoma with proliferating normal human skin fibroblasts abrogated retinol esterification within 96 h and increased the expression of the active form of TGFß-1 by 2.4-fold. A concomitant 3.2-fold downregulation of CRBP-1 expression took place. This is the first study to (1) demonstrate an association between retinyl ester synthesis and cutaneous melanoma morphological phenotypes; (2) suggest the existence of a soluble, diffusible inhibitor of the retinol esterification pathway; (3) report the ability of the isolated, proliferating human epidermal melanocyte to esterify retinol; and (4) provide evidence of DNA variants in the coding region of LRAT.
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