Sp3 Is a Transcriptional Repressor of Transforming Growth Factor-β Receptors

Sudhakar Ammanamanchi,Michael G Brattain

doi:10.1074/jbc.m002462200

Sudhakar Ammanamanchi, Michael G Brattain

Open Access

https://doi.org/10.1074/jbc.m002462200

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Abstract

MCF-7E breast cancer cells express transforming growth factor-beta (TGF-beta) receptors RI and RII in comparison to MCF-7L cells. We present data showing that Sp3 acts as a transcriptional repressor of RI and RII in MCF-7L cells and GEO colon cancer cells. MCF-7L and GEO cells express high levels of Sp3 protein. Gel shift analysis indicated enhanced binding of Sp3 from MCF-7L cells to a consensus Sp1 oligonucleotide. Southwestern data indicated increased binding of Sp3 to RI and RII promoters in MCF-7L cells, suggesting a correlation between Sp3 binding and reduced expression of TGF-beta receptors in MCF-7L cells. Cotransfection of CMV-Sp3 cDNA with RI and RII promoter-luciferase reporter constructs decreased RI and RII promoter activities by 70% in MCF-7E and GEO cells. Southwestern analysis detected the binding of transiently expressed Sp3 to RI and RII promoters in MCF-7E cells. Significantly, ectopic Sp3 expression led to repression of RI and RII transcripts in MCF-7E cells. This report demonstrates that inappropriate overexpression of Sp3 is a mechanism that contributes to repression of TGF-beta receptors.

Highlights

One of the crucial roles of TGF-␤ is the growth inhibition of normal epithelial cells as well as some cancer cells
We present data showing that Sp3 acts as a transcriptional repressor of RI and RII in MCF-7 late passage cells (MCF-7L) cells and GEO colon cancer cells
MCF-7L and GEO cells showed significantly higher levels of all the three Sp3 isoforms in comparison to MCF-7 early passage (MCF-7E) cells, whereas there were no differences in the c-Jun levels, indicating selectivity of Sp3 modulation

Summary

Introduction

One of the crucial roles of TGF-␤ is the growth inhibition of normal epithelial cells as well as some cancer cells. This Sp3 antibody has previously been reported to cause similar depletion of the protein-DNA complexes following incubation with endothelial cell nuclear extracts prior to the addition of 32P-labeled kinase domain receptor promoter of the vascular endothelial growth factor [26].

Results

Conclusion