Spontaneous differentiation of normal diploid osteoblasts in culture is accompanied by increased cyclin E associated kinase activity on (1) the retinoblastoma susceptibility protein pRB, (2) the p107 RB related protein, and (3) two endogenous cyclin E-associated substrates of 78 and 105 kD. Activity of the differentiation-related cyclin E complexes (diff.ECx) is not recovered in cdc2 or cdk2 immunoprecipitates. Phosphorylation of both the 105 kD endogenous substrate and the p107 exogenous substrate is sensitive to inhibitory activity (diff.ECx-i) present in proliferating osteoblasts. This inhibitory activity is readily recruited by the cyclin E complexes of differentiated osteoblasts but is not found in cyclin E immunoprecipitates of the proliferating cells themselves. Strong inhibitory activity on diff.ECx kinase activity is excerted by proliferating ROS 17/2.8 osteosarcoma cells. However, unlike the normal diploid cells, the diff.ECx-i activity of proliferating ROS 17/2.8 cells is recovered by cyclin E immunoprecipitation. The cyclin-dependent kinase inhibitor p21 CIP1/WAF1 inhibits diff.ECx kinase activity. Thus, our results suggest the existence of a unique regulatory system, possibly involving p21 CIP1/WAF1, in which inhibitory activity residing in proliferating cells is preferentially targeted towards differentiation-related cyclin E-associated kinase activity.
Smith, E., Frenkel, B., Maclachlan, T.K., Giordano, A., Stein, J.L., Lian, J.B., et al. (1997). Post-proliferative cyclin E-associated kinase activity in differentiated osteoblasts: inhibition by proliferating osteoblasts and osteosarcoma cells. JOURNAL OF CELLULAR BIOCHEMISTRY, 66(2), 141-152 [10.1002/(SICI)1097-4644(19970801)66:2<141::AID-JCB2>3.0.CO;2-Q].
Post-proliferative cyclin E-associated kinase activity in differentiated osteoblasts: inhibition by proliferating osteoblasts and osteosarcoma cells
Giordano A.;
1997-01-01
Abstract
Spontaneous differentiation of normal diploid osteoblasts in culture is accompanied by increased cyclin E associated kinase activity on (1) the retinoblastoma susceptibility protein pRB, (2) the p107 RB related protein, and (3) two endogenous cyclin E-associated substrates of 78 and 105 kD. Activity of the differentiation-related cyclin E complexes (diff.ECx) is not recovered in cdc2 or cdk2 immunoprecipitates. Phosphorylation of both the 105 kD endogenous substrate and the p107 exogenous substrate is sensitive to inhibitory activity (diff.ECx-i) present in proliferating osteoblasts. This inhibitory activity is readily recruited by the cyclin E complexes of differentiated osteoblasts but is not found in cyclin E immunoprecipitates of the proliferating cells themselves. Strong inhibitory activity on diff.ECx kinase activity is excerted by proliferating ROS 17/2.8 osteosarcoma cells. However, unlike the normal diploid cells, the diff.ECx-i activity of proliferating ROS 17/2.8 cells is recovered by cyclin E immunoprecipitation. The cyclin-dependent kinase inhibitor p21 CIP1/WAF1 inhibits diff.ECx kinase activity. Thus, our results suggest the existence of a unique regulatory system, possibly involving p21 CIP1/WAF1, in which inhibitory activity residing in proliferating cells is preferentially targeted towards differentiation-related cyclin E-associated kinase activity.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/11365/36970
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