The Homeodomain Protein CDP Regulates Mammary-Specific Gene Transcription and Tumorigenesis

Abstract

The CCAAT-displacement protein (CDP) has been implicated in developmental and cell-type-specific regulation of many cellular and viral genes. We previously have shown that CDP represses mouse mammary tumor virus (MMTV) transcription in tissue culture cells. Since CDP-binding activity for the MMTV long terminal repeat declines during mammary development, we tested whether binding mutations could alter viral expression. Infection of mice with MMTV proviruses containing CDP binding site mutations elevated viral RNA levels in virgin mammary glands and shortened mammary tumor latency. To determine if CDP has direct effects on MMTV transcription rather than viral spread, virgin mammary glands of homozygous CDP-mutant mice lacking one of three Cut repeat DNA-binding domains (ΔCR1) were examined by reverse transcription-PCR. RNA levels of endogenous MMTV as well as α-lactalbumin and whey acidic protein (WAP) were elevated. Heterozygous mice with a different CDP mutation that eliminated the entire C terminus and the homeodomain (ΔC mice) showed increased levels of MMTV, β-casein, WAP, and α-lactalbumin RNA in virgin mammary glands compared to those from wild-type animals. No differences in amounts of WDNM1, ε-casein, or glyceraldehyde-3-phosphate dehydrogenase RNA were observed between the undifferentiated mammary tissues from wild-type and mutant mice, indicating the specificity of this effect. These data show independent contributions of different CDP domains to negative regulation of differentiation-specific genes in the mammary gland.

We acknowledge helpful discussions and comments on the manuscript by Jon Huibregtse and members of the Dudley laboratory. We also thank Dan Medina for analysis of mammary tumor histology.

This work was supported by grants CA34780 from the National Institutes of Health and DAMD17-01-1-0424 from the U.S. Army Breast Cancer Research Program.