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A more recent version of this article appeared on April 1, 2004
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Submitted on December 5, 2003
Revised on January 7, 2004
Accepted on January 8, 2004
1 Cell Biology, Zoological Institute, Technical University of Braunschweig, D-38092 Braunschweig, Germany
2 Tumor Genetics, Max-Delbrück-Center for Molecular Medicine, D-13092 Berlin-Buch, Germany
3 Cell Biology, Zoological Institute, Technical University of Braunschweig, D-38092 Braunschweig, Germany, BD Biosciences, D-69126 Heidelberg, Germany
4 atugen AG, D-13125 Berlin-Buch, Germany
5 Clinic of Surgery and Surgical Oncology, Robert Rössle Hospital, D-13122 Berlin-Buch, Germany
* Corresponding author. E-mail address: bmj{at}tu-bs.de.
Profilin 1 (PFN1) is a regulator of the microfilament system and involved in various signaling pathways. It interacts with many cytoplasmic and nuclear ligands. The importance of PFN1 for human tissue differentiation has been demonstrated by the findings that human cancer cells, expressing conspicuously low PFN1 levels, adopt a nontumorigenic phenotype upon raising their PFN1 level. In the present study, we characterize the ligand binding site crucial for profilins tumor suppressor activity. Starting with CAL51, a human breast cancer cell line highly tumorigenic in nude mice, we established stable clones that express PFN1 mutants differentially defective in ligand binding. Clones expressing PFN1 mutants with reduced binding to either poly-proline-stretch ligands or phosphatidyl-inositol-4,5-bisphosphate, but with a functional actin-binding site, were normal in growth, adhesion and anchorage dependence, with only a weak tendency to elicit tumors in nude mice, similar to controls expressing wild-type PFN1. In contrast, clones expressing a mutant with severely reduced capacity to bind actin still behaved like the parental CAL51 and was highly tumorigenic. We conclude that the actin-binding site on profilin is instrumental for normal differentiation of human epithelia and the tumor suppressor function of PFN1.
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