QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fan, G. Articles by Steer, C. J. Search for Related Content PubMed PubMed Citation Articles by Fan, G. Articles by Steer, C. J.

Unbound E2F modulates TGF-ß1-induced apoptosis in HuH-7 cells

¹ Department of Medicine, University of Minnesota Medical School, Minneapolis, MN 55455, USA
² Department of Genetics, Cell Biology, and Development, University of Minnesota Medical School, Minneapolis, MN 55455, USA

^* Author for correspondence (e-mail: steer001{at}tc.umn.edu )

Accepted 13 May 2002

E2F is an important target of the retinoblastoma protein (pRb) and plays a critical role in G₁/S progression through the cell cycle. TGF-ß1 arrests HuH-7 cells in G₁ by suppressing phosphorylation of pRb and induces apoptosis by inhibiting its expression. In this study, we examined the downstream effects of TGF-ß1-induced apoptosis and the potential roles for pRb and E2F. The results indicated that greater than 90% of the TGF-ß1-induced preapoptotic cells were arrested in G₁ phase of the cell cycle. This was associated with a significant increase in both E2F-DNA-binding activity and transcription of E2F-responsive reporter constructs. In contrast, no significant changes were observed in E2F mRNA and protein levels, and the overexpression of pRb partially inhibited E2F activation. Gel-shift assays identified more than four E2F complexes from preapoptotic and synchronized G₁ HuH-7 cells, each exhibiting different patterns of E2F-associated proteins. The increased E2F activity did not affect the association patterns with pRb, p107 and p130, but altered the formation of an E2F—DP-1 complex. In contrast, E2F—DP-2 exhibited little change in the preapoptotic cells. Moreover, TGF-ß1 induced apoptosis at G₁ and inhibited entry into S phase irrespective of the increased E2F activity. The release of preapoptotic cells from TGF-ß1 resulted in rapid S phase entry and subsequent apoptosis in 33% of cells over a 72 hour period. In conclusion, the results demonstrate that TGF-ß1-induced apoptosis in HuH-7 cells is associated with a marked increase in activity of transcription factor E2F that is partially inhibited by overexpression of pRb. Preapoptotic changes are, in part, reversible upon removal of TGF-ß1 and the majority of cells re-enter the normal cell cycle. Finally, TGF-ß1-induced apoptosis with the associated increase in E2F activity can occur in both the G₁ and S phases of the cell cycle.

Key words: Apoptosis, Cytokine, E2F transcription factors, Human hepatoma cells, TGF-ß1

This article has been cited by other articles:

				S. Sola, X. Ma, R. E. Castro, B. T. Kren, C. J. Steer, and C. M. P. Rodrigues Ursodeoxycholic Acid Modulates E2F-1 and p53 Expression through a Caspase-independent Mechanism in Transforming Growth Factor {beta}1-induced Apoptosis of Rat Hepatocytes J. Biol. Chem., December 5, 2003; 278(49): 48831 - 48838. [Abstract] [Full Text] [PDF]