Alteration of pRb/p16/cdk4 regulation in human osteosarcoma.
Cell-cycle regulation depends on a fine balance between cyclin-cyclin-dependent kinase complexes and a family of kinase inhibitors that bind cyclin-cdk complexes and block their activity. To investigate the role of mechanisms regulating cell-cycle progression in human osteosarcomas (OS), pRb/p16/cdk4 expression was analyzed in 39 high-grade OS; 19 of these developed metastasis during follow-up. Positive reaction for functional pRB was shown by 18/39 (46%) OS, while 21/39 (54%) were negative. A higher probability of metastasis was seen in patients with negative pRb expression (p < 0.05). Furthermore, while functional pRb and D1 expression are inversely associated to metastasis occurrence, the presence of D1/cdk4 complex in our study was related to poor prognosis. We found that 10/18 pRb-positive and 14/21 pRb-negative tumors were p16-positive. No significant correlation was found between pRb and p16 expression. On the other hand, high cdk4 levels in p16-positive tumors as compared with p16-negative tumors resulted in a positive association between p16 and cdk4 expression (Chi squared = 5.98; p = 0.01). No extensive p16INK4A genomic alterations were found in tumors lacking p16-protein expression. To determine which mechanisms are involved in the down-regulation of p16 protein, the methylation status of the p16INK4 gene was evaluated on the 15 p16-negative tumors: 8 samples showed 5' CpG-island methylation; 4/8 had a complete methylation status, while in the remaining 4 the gene was only partially methylated. These data confirm the role of the pRb/p16/cdk4 pathway in OS development.
Benassi
M S
MS
Department of Musculoskeletal Oncology, Laboratory of Oncologic Research, Rizzoli Orthopedic Institute, Bologna, Italy. mariaserena.benassi@ior.it
Molendini
L
L
Gamberi
G
G
Ragazzini
P
P
Sollazzo
M R
MR
Merli
M
M
Asp
J
J
Magagnoli
G
G
Balladelli
A
A
Bertoni
F
F
Picci
P
P
D015153:Blotting, Western; D001859:Bone Neoplasms / Q000737:chemistry* / Q000235:genetics / Q000473:pathology; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000032:analysis*; D018844:Cyclin-Dependent Kinases / Q000032:analysis*; D019175:DNA Methylation; D005500:Follow-Up Studies; D019942:Genes, p16; D006801:Humans; D012516:Osteosarcoma / Q000737:chemistry* / Q000235:genetics / Q000473:pathology; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000032:analysis*
D019941:Cyclin-Dependent Kinase Inhibitor p16; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases