Overexpression of Cdk6 and Ccnd1 in chondrocytes inhibited chondrocyte maturation and caused p53-dependent apoptosis without enhancing proliferation

摘要: Cell proliferation and differentiation are closely coupled. However, we previously showed that overexpression of cyclin-dependent kinase (Cdk6) blocks chondrocyte without affecting cell-cycle progression in vitro. To investigate whether Cdk6 inhibits vivo, generated chondrocyte-specific transgenic mice using Col2a1 promoter. Unexpectedly, chondrocytes the were similar to those wild-type mice. Then, Ccnd1 Cdk6/Ccnd1 double possibility through E2f activation. Bromodeoxyuridine (BrdU)-positive terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive increased number, maturation was inhibited only (K6(H)/D1(H) mice), which dwarfism. Retinoblastoma protein (pRb) highly phosphorylated but p107 upregulated, expression target genes dysregulated as shown by upregulation Cdc6 downregulation cyclin E, dihydrofolate reductase (dhfr), Cdc25a B-Myb K6(H)/D1(H) Similarly, a chondrogenic cell line ATDC5 pRb, upregulated p107, induced apoptosis, downregulated dhfr small interfering RNA reversed genes. Further, introduction kinase-negative D1 abolished all effects Cdk6/cyclin cells, indicating requirement activity on these effects. p53 deletion partially restored size skeleton almost completely rescued failed enhance These findings indicated enhanced G1/S transition phosphorylating accomplish cycle, underwent p53-dependent apoptosis probably due dysregulation Our also addition inactivation Rb not sufficient accelerate proliferation, suggesting resistance sarcomagenesis.