
<ArticleTitle>Cloning and characterization of ectopically expressed transcripts for the <prot>actin</prot>-binding protein <prot>MIPP</prot> in mouse mammary carcinomas.</ArticleTitle>
<AbstractText><prot>Mipp</prot> is a kelch-related, placental-specific gene that is ectopically expressed in many BALB/c mouse mammary carcinomas of various etiologies. The Kelch family encompasses proteins that are emerging as key links between microfilaments and a variety of cellular structures and functions. Mouse mammary tumors express two <prot>mipp</prot> transcripts (2.2 and 5.6 kb). We cloned the 2.2 kb <prot>mipp</prot> mRNA and analysed the product of its 1.7 kb ORF. The 584 residue <prot>MIPP</prot> protein has an N-terminal BTB domain and six C-terminal tandem Kelch repeats. Despite expression of two <prot>mipp</prot> RNAs, only a single <prot>MIPP</prot> protein is expressed in mammary tumors. <prot>MIPP</prot> protein binds to microfilaments in vitro and co-immunoprecipitates with <prot>actin</prot>. <prot>MIPP</prot> co-localized with <prot>concanavalin A</prot> at the endoplasmic reticulum, suggesting that <prot>MIPP</prot> might mediate interactions between <prot>microtubules</prot> and <prot>actin</prot> filaments. Because <prot>MIPP</prot> expression is widespread in mouse mammary tumors, it might contribute to tumorigenesis. Although <prot>MIPP</prot> had little effect on the growth rate of human breast cell lines following transfection, it greatly reduced the formation of duct-like structures on reconstituted basement membrane. Our results suggest that <prot>MIPP</prot> could contribute to malignant progression in the mouse mammary epithelial cells by perverting their response to cues from the extracellular matrix.</AbstractText>
