Roles of E2F1 in mesangial cell proliferation in vitro.
Roles of E2F1 in mesangial cell proliferation in vitro.


BACKGROUND
The proliferation of mesangial cells is a common feature of many glomerular diseases. E2F transcription factors play an important role in the regulation of the cell cycle. However, the regulation of the mesangial cell cycle and the participation of the E2F family (E2F1 through E2F5) in mesangial cells have not been clarified. Therefore, we investigated the roles of the E2F family in the mesangial cell cycle.


METHODS
To elucidate the importance of the E2F family, we investigated the mesangial cell cycle by examining the cell count and thymidine incorporation, and compared it with the protein expression of E2F. Using adenovirus-mediated gene transfer, the cell cycle and apoptosis were examined by measurement of thymidine incorporation, flow cytometry, and caspase 3 activity. We also studied the interaction between E2F1 and G1 cyclins by promoter assay, Western blotting, and CDK kinase assay.


RESULTS
E2F1 increased 20-fold in G1/S phase transition. E2F1 overexpression facilitated the mesangial cell cycle and later induced apoptosis. Furthermore, E2F1 overexpression increased the promoter activities and protein expressions of G1 cyclins, cyclin D1, cyclin E, cyclin A. The up-regulation of G1 cyclins contributed to the activation of CDK4 and CDK2.


CONCLUSIONS
In mesangial cells, we conclude that E2F1 plays an important role in G1/S phase transition and in apoptosis. E2F1 regulates the mesangial cell cycle through two distinct pathways. First, E2F1 directly transcribes genes that are necessary for DNA synthesis, and second, it promotes cell cycle progression via the induction of G1 cyclins.
Inoshita
S
S
Second Department of Internal Medicine, Tokyo Medical and Dental University, Tokyo, Japan.
Terada
Y
Y
Nakashima
O
O
Kuwahara
M
M
Sasaki
S
S
Marumo
F
F
D000256:Adenoviridae; D000257:Adenoviridae Infections; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001798:Blood Proteins / Q000494:pharmacology; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D019925:Cyclin A / Q000235:genetics; D019938:Cyclin D1 / Q000235:genetics; D019927:Cyclin E / Q000235:genetics; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050700:E2F5 Transcription Factor; D015967:Gene Expression Regulation, Viral; D005920:Glomerular Mesangium / Q000166:cytology* / Q000201:enzymology; D005921:Glomerulonephritis / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D011401:Promoter Regions, Genetic / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D056465:Retinoblastoma-Binding Protein 1; D013936:Thymidine / Q000378:metabolism / Q000494:pharmacology; D013997:Time Factors; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation / Q000502:physiology; D014316:Tritium
D001798:Blood Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019925:Cyclin A; D019927:Cyclin E; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050700:E2F5 Transcription Factor; C493755:E2f1 protein, rat; D011518:Proto-Oncogene Proteins; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D014316:Tritium; D019938:Cyclin D1; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; C495903:Cdk4 protein, rat; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D013936:Thymidine