D-type cyclin expression is decreased and p21 and p27 CDK inhibitor expression is increased when tsBN462 CCG1/TAFII250 mutant cells arrest in G1 at the restrictive temperature.
BACKGROUND
The tsBN462 temperature-sensitive mutant hamster cell line exhibits cell cycle arrest and apoptosis at the restrictive temperature of 39.5 degrees C, due to a point mutation in the CCG1/TAFII250 gene, which encodes a component of the general transcription factor TFIID.


RESULTS
We now report that CCG1/TAFII250 persisted as a complex with TBP and associated proteins (TAFs) in tsBN462 cells at the restrictive temperature. FACScan analysis revealed that the tsBN462 mutation resulted in a failure to progress out of G0 into G1. Using two-dimensional gel electrophoresis we observed a decrease in the synthesis of several proteins, starting in the middle of the G1 phase, becoming very pronounced during late G1. The expression of the immediate early genes c-fos, c-jun and c-myc was normally induced by serum treatment of quiescent cells at the restrictive temperature, whereas expression of cyclins A, D1 and D3 was reduced. Expression of the cyclin-dependent kinase (CDK) inhibitor proteins p21 and p27 was enhanced. Consistent with the decreased cyclin D and increased p21/p27 expression, we found that phosphorylation of Rb was decreased at 39.5 degrees C. Cyclin A-, E- and Cdk2-associated histone H1 kinase activity was reduced concomitantly with the increase in p21 protein.


CONCLUSIONS
Decreased cyclin/Cdk kinase activity and decreased Rb phosphorylation are possible causes of G1 cell cycle arrest in tsBN462 cells at the restrictive temperature.
Sekiguchi
T
T
Molecular Biology and Virology Laboratory, Salk Institute, La Jolla, CA 92037, USA.
Noguchi
E
E
Hayashida
T
T
Nakashima
T
T
Toyoshima
H
H
Nishimoto
T
T
Hunter
T
T
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D056741:Cyclin D; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016213:Cyclins / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D016193:G1 Phase / Q000235:genetics; D015870:Gene Expression; D017781:Genes, Immediate-Early; D051548:Histone Acetyltransferases; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics*; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000378:metabolism; D035381:TATA-Binding Protein Associated Factors; D013696:Temperature; D035362:Transcription Factor TFIID
D056741:Cyclin D; D016213:Cyclins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016160:Retinoblastoma Protein; D035381:TATA-Binding Protein Associated Factors; D035362:Transcription Factor TFIID; D051548:Histone Acetyltransferases; C069001:TATA-binding protein associated factor 250 kDa; D018844:Cyclin-Dependent Kinases