Differential expression of G1 cyclins and cyclin-dependent kinase inhibitors in normal and transformed melanocytes.
OBJECTIVE
To investigate the levels of the different regulatory proteins involved in the G1 progression and G1/S transition in normal and transformed human choroidal melanocytes (CM).


METHODS
Three choroidal melanoma cell lines and three CM cultures were used. The purity of the CM cultures was assessed by different approaches, including morphologic study, specific immunostaining, cell proliferation behavior, and transforming growth factor-beta1 responsiveness. The cell cycle protein levels were evaluated by specific immunoblotting of total extracts obtained from the different cell lines.


RESULTS
Alterations were observed in the expression of cylins D1 and E in the transformed cells, whereas the amounts of the cyclin-dependent kinases (CDKs) CDK2 and CDK4 were almost identical in both cell types. Although the expression of cyclin H was slightly increased in transformed cells, neither the CDK7 level nor the CDK7 and cyclin H localizations were altered when compared with those in normal CM. The results suggest the absence of the CDK inhibitor (CKI) p21 in two of the three melanoma cell lines and, as a main feature, a striking underexpression of p27 in the three transformed cell lines. Finally, although the p16 level was almost the same in normal and transformed cells, a loss of p16-CDK4 interaction was observed in two of the three melanoma cell lines.


CONCLUSIONS
Deregulated expression of G1 cyclins and CKIs and alteration in the interaction of CKIs with CDKs may be implicated in the neoplastic transformation of human ocular melanocytes to malignant melanoma cells.
Mouriaux
F
F
Institut National de la Santé et de la Recherche Médicale, Contrat Jeune Formation 95-10 (Institut Fédératif de Recherche 30), Toulouse, France.
Casagrande
F
F
Pillaire
M J
MJ
Manenti
S
S
Malecaze
F
F
Darbon
J M
JM
D002455:Cell Division; D002461:Cell Line, Transformed / Q000378:metabolism / Q000473:pathology; D002830:Choroid Neoplasms / Q000378:metabolism* / Q000473:pathology; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D019084:Fluorescent Antibody Technique, Indirect; D016193:G1 Phase; D006801:Humans; D015151:Immunoblotting; D007124:Immunoenzyme Techniques; D008544:Melanocytes / Q000378:metabolism* / Q000473:pathology; D008545:Melanoma / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000378:metabolism / Q000473:pathology; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014407:Tumor Cells, Cultured
D016213:Cyclins; D016212:Transforming Growth Factor beta; D018844:Cyclin-Dependent Kinases