Document Detail

Inhibition of topoisomerase IIalpha expression by transforming growth factor-beta1 is abrogated by the papillomavirus E7 protein.
MedLine Citation:
PMID:  11156401     Owner:  NLM     Status:  MEDLINE    
Transforming growth factor-beta (TGF-beta) protects normal cells from etoposide-induced cell death, yet the mechanism has remained speculative. Studies have shown that etoposide modifies the activity of the topoisomerase IIalpha (topo IIalpha) enzyme, thereby causing DNA damage and inducing cell death. Expression of topo IIalpha is necessary for etoposide-induced cell death, and peak expression of topo IIalpha normally occurs during the G2 phase of the cell cycle. We predicted that by arresting growth in the G1 phase, TGF-beta1 would prevent the induction of topo IIalpha expression that normally occurs subsequent to the G1-S transition, thereby protecting cells from etoposide-induced cell death. Accordingly, we hypothesized that the inhibition of topo IIalpha expression by TGF-beta1 would be dependent on the ability of TGF-beta1 to arrest cell cycle progression in G1. Using mink lung epithelial cells (MvlLu), we found that TGF-beta1 decreases topo IIalpha mRNA expression, and the decrease occurs as cells begin to accumulate in the G1 phase of the cell cycle. Topo IIalpha protein expression decreases subsequent to the fall in mRNA expression. In contrast, topo IIalpha expression is not affected by TGF-beta1 in cells that fail to undergo G1 arrest because of inactivation of the retinoblastoma tumor suppressor protein (pRb) by the papillomavirus type 16 E7 protein. Our studies suggest that inhibition of topo IIalpha by TGF-beta1 is the principal mechanism that protects mink lung epithelial cells (Mv1Lu) from etoposide-induced toxicity. Furthermore, the inhibition of topo IIalpha protein expression by TGF-beta1 is dependent on pRb-mediated cell cycle arrest, suggesting that TGF-beta1 will not reduce the sensitivity of pRb-deficient cancers to etoposide.
D J Satterwhite; R L White; N Matsunami; K L Neufeld
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Cancer research     Volume:  60     ISSN:  0008-5472     ISO Abbreviation:  Cancer Res.     Publication Date:  2000 Dec 
Date Detail:
Created Date:  2001-01-11     Completed Date:  2001-02-22     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  2984705R     Medline TA:  Cancer Res     Country:  United States    
Other Details:
Languages:  eng     Pagination:  6989-94     Citation Subset:  IM    
Department of Pediatrics, University of Utah School of Medicine, Salt Lake City 84132, USA.
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MeSH Terms
Antigens, Neoplasm
Antineoplastic Agents, Phytogenic / pharmacology
Blotting, Northern
Blotting, Western
Cell Cycle / drug effects
Cell Death / drug effects
Cell Line
Cell Separation
DNA Topoisomerases, Type II / antagonists & inhibitors*
DNA Topoisomerases, Type II, Eukaryotic*
DNA-Binding Proteins
Etoposide / pharmacology
Flow Cytometry
G1 Phase / drug effects
Isoenzymes / antagonists & inhibitors*
Nucleic Acid Synthesis Inhibitors / pharmacology
Oncogene Proteins, Viral / pharmacology*
RNA, Messenger / metabolism
Retroviridae / genetics
S Phase / drug effects
Time Factors
Transforming Growth Factor beta / pharmacology*
Transforming Growth Factor beta1
Reg. No./Substance:
0/Antigens, Neoplasm; 0/Antineoplastic Agents, Phytogenic; 0/DNA-Binding Proteins; 0/Isoenzymes; 0/Nucleic Acid Synthesis Inhibitors; 0/Oncogene Proteins, Viral; 0/RNA, Messenger; 0/TGFB1 protein, human; 0/Transforming Growth Factor beta; 0/Transforming Growth Factor beta1; 0/oncogene protein E7, Human papillomavirus type 16; 33419-42-0/Etoposide; EC 5.99.1.-/DNA Topoisomerases, Type II, Eukaryotic; EC Topoisomerases, Type II; EC topoisomerase II alpha

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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