Effect of TGF-beta1 on cell cycle regulatory proteins in LPS-stimulated normal mouse B lymphocytes.
The cell cycle events accompanying TGF-beta1-induced growth arrest of normal mouse resting B lymphocytes stimulated by LPS were investigated. We showed that TGF-beta1 prevents the retinoblastoma protein (pRb) phosphorylation and induces growth arrest in mid- to late G1. To explore the molecular basis of the effect of TGF-beta1, we analyzed the in vitro kinase activities of cyclin/cyclin-dependent kinase (cdk) complexes involved in the progression through G1 phase and in the G1/S transition, by using the glutathione S-transferase-pRb fusion protein as a substrate. Cdk2-associated kinase activity was strongly induced in mitogen-treated B cells. It was dramatically inhibited by TGF-beta1 as were the cyclin E- and cyclin A-dependent kinase activities. TGF-beta1 treatment had no significant effect on the expression of two G1/S phase proteins, cyclin E and cdk2. In contrast, the appearance of cyclin A, occuring in late G1 phase, was almost totally inhibited by TGF-beta1. We also showed that expression of the cdk inhibitor protein p27Kip1 decreased as cells progressed through the G1 phase. An accumulation of p27 was found in TGF-beta1-treated cells, showing that TGF-beta1 prevented LPS-induced decline of p27. Finally we found that the lack of kinase activity associated with cyclin E/cdk2 complexes was correlated with increased amounts of cdk2- and cyclin E-bound p27. Overall, these results suggest that both cyclin A and cdk2 may be active participants in the TGF-beta1-induced cell cycle arrest in normal mouse B cells and indicate the involvement of p27 in this mechanism.
Bouchard
C
C
Laboratoire d'Immunologie Cellulaire et Clinique, INSERM U255, Institut Curie, Paris, France.
Fridman
W H
WH
Sautès
C
C
D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D002453:Cell Cycle / Q000276:immunology*; D018797:Cell Cycle Proteins / Q000276:immunology / Q000378:metabolism*; D005434:Flow Cytometry; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D015398:Signal Transduction / Q000276:immunology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D018797:Cell Cycle Proteins; D008070:Lipopolysaccharides; D016212:Transforming Growth Factor beta