The WT1 Wilms' tumor suppressor gene product interacts with estrogen receptor-alpha and regulates IGF-I receptor gene transcription in breast cancer cells.
The IGF-I receptor (IGF-IR) has an important role in breast cancer development and progression. Previous studies have suggested that the IGF-IR gene is negatively regulated by a number of transcription factors with tumor suppressor activity, including the Wilms' tumor protein WT1. The present study was aimed at evaluating the hypothesis that IGF-IR gene transcription in breast cancer cells is under inhibitory control by WT1 and, furthermore, that the mechanism of action of WT1 involves functional and physical interactions with estrogen receptor-alpha (ERalpha). Results of transient coexpression experiments showed that all four predominant isoforms of WT1 (including or lacking alternatively spliced exons 5 and 9) repressed IGF-IR promoter activity by 39-49%. To examine the potential interplay between WT1 and ERalpha in control of IGF-IR gene transcription we employed ER-depleted C4 cells that were generated by clonal selection of ER-positive MCF-7 cells that were maintained in estrogen-free conditions. IGF-IR levels in C4 cells were approximately 43% of the values in MCF-7 cells whereas WT1 levels in C4 cells were 4.25-fold higher than in MCF-7. Triple cotransfection experiments using an ERalpha expression vector in the absence or presence of WT1 expression vectors, along with an IGF-IR promoter reporter plasmid, revealed that ERalpha stimulated IGF-IR promoter activity whereas coexpression of WT1 abrogated the effect of ERalpha. In addition, co-immunoprecipitation experiments demonstrated a specific association between WT1 and ERalpha. Combined, our results suggest that WT1 suppresses IGF-IR gene transcription in breast cancer cells via a mechanism that involves protein-protein association with ERalpha. As a result of this interaction, the ability of ERalpha to transactivate the IGF-IR promoter is abrogated. These findings are consistent with a potential tumor suppressor role for WT1 in breast cancer and suggest that WT1 inactivation in tumoral cells may result in deregulated IGF-IR gene expression and enhanced mitogenic activation by locally produced and/or circulating IGFs.
Reizner
Naama
N
Department of Clinical Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
Maor
Sharon
S
Sarfstein
Rive
R
Abramovitch
Shirley
S
Welshons
Wade V
WV
Curran
Edward M
EM
Lee
Adrian V
AV
Werner
Haim
H
D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism*; D045744:Cell Line, Tumor; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D005260:Female; D016162:Genes, Wilms Tumor; D006801:Humans; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000235:genetics*; D014158:Transcription, Genetic; D025721:WT1 Proteins / Q000235:genetics / Q000378:metabolism*
D004273:DNA, Neoplasm; D047628:Estrogen Receptor alpha; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D025721:WT1 Proteins; D017526:Receptor, IGF Type 1