The p16-cyclin D/Cdk4-pRb pathway as a functional unit frequently altered in melanoma pathogenesis.
The p16Ink4/CDKN2, D-type cyclins, their partners Cdk4/Cdk6, and pRb constitute a G1 regulatory pathway commonly targeted in tumorigenesis. Genetic, immunochemical, and functional cell cycle analyses showed abnormalities of this pathway in each of 22 human melanoma cell lines examined. Normal melanocytes and all melanoma lines expressed Cdk4, Cdk6, and cyclins D1 and D3. The tumor suppressors p16Ink4/CDKN2 and pRb were lost in 17 and 4 cases, respectively, due to various genetic mechanisms, including transcriptional block of p16 and nonsense mutations of RB1. Ectopic expression of p16 prevented S-phase entry of Rb+/p16- but not Rb-deficient melanoma lines. The SK29-MEL-1 cell line harboring an R24C mutation in Cdk4 expressed wild-type pRb and overabundant p16, the latter preventing endogenous Cdk6 but not Cdk4 from associating with cyclin D1. Microinjection of cyclin D1-neutralizing antibody arrested the SK29-MEL-1 cells in G1, whereas pl6 did not, indicating that the cyclin D1/Cdk4-R24C complex is required for G1 progression, and the resistance of the complex to p16 in vivo. These data strongly support the candidacy of Cdk4 as a novel proto-oncogene, provide further evidence for the p16-cyclin D/Cdk-pRb pathway as a functional unit, and suggest that deregulation of this checkpoint may represent a common step in the multistep progression of sporadic malignant melanomas.
Bartkova
J
J
Division of Cancer Biology, Danish Cancer Society, Copenhagen, Denmark.
Lukas
J
J
Guldberg
P
P
Alsner
J
J
Kirkin
A F
AF
Zeuthen
J
J
Bartek
J
J
D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D056741:Cyclin D; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000502:physiology*; D016213:Cyclins / Q000235:genetics / Q000502:physiology*; D018450:Disease Progression; D016193:G1 Phase / Q000502:physiology*; D017353:Gene Deletion; D016161:Genes, Retinoblastoma; D006801:Humans; D008545:Melanoma / Q000209:etiology* / Q000235:genetics / Q000503:physiopathology; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D011519:Proto-Oncogenes; D016160:Retinoblastoma Protein / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D056741:Cyclin D; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016213:Cyclins; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases