The p53 homologue p63 encodes for different isotypes able to either transactivate p53 reporter genes (TAp63) or act as p53-dominant-negatives (DeltaNp63). p63 is expressed in the basal cells of many epithelial organs and its germline inactivation in the mouse results in agenesis of organs such as skin appendages and the breast. Here, we show that prostate basal cells, but not secretory or neuroendocrine cells, express p63. In addition, prostate basal cells in culture predominantly express the DeltaNp63alpha isotype. In contrast, p63 protein is not detected in human prostate adenocarcinomas. Finally, and most importantly, p63(-/-) mice do not develop the prostate. These results indicate that p63 is required for prostate development and support the hypothesis that basal cells represent and/or include prostate stem cells. Furthermore, our results show that p63 immunohistochemistry may be a valuable tool in the differential diagnosis of benign versus malignant prostatic lesions.

Estrogen receptor (ER) expression and Her-2 amplification define specific subsets of breast tumors for which specific therapies exist. The S-phase kinase-associated protein Skp2 is required for the ubiquitin-mediated degradation of the cdk-inhibitor p27 and is a bona fide proto-oncoprotein. Using microarray analysis and immunohistochemistry, we determined that higher levels of Skp2 are present more frequently in ER-negative tumors than in ER-positive cases. Interestingly, the subset of ER-negative breast carcinomas overexpressing Skp2 are also characterized by high tumor grade, negativity for Her-2, basal-like phenotype, high expression of certain cell cycle regulatory genes, and low levels of p27 protein. We also found that Skp2 expression is cell adhesion-dependent in normal human mammary epithelial cells but not in breast cancer cells and that an inhibition of Skp2 induces a decrease of adhesion-independent growth in both ER-positive and ER-negative cancer cells. Finally, forced expression of Skp2 abolished effects of antiestrogens, suggesting that deregulated Skp2 expression might play a role in the development of resistance to antiestrogens. We conclude that Skp2 has oncogenic potential in breast epithelial cells and is overexpressed in a subset of breast carcinomas (ER- and Her-2 negative) for which Skp2 inhibitors may represent a valid therapeutic option.

Estrogen receptor (ER) expression and Her-2 amplification define specific subsets of breast tumors for which specific therapies exist. The S-phase kinase-associated protein Skp2 is required for the ubiquitin-mediated degradation of the cdk-inhibitor p27 and is a bona fide proto-oncoprotein. Using microarray analysis and immunohistochemistry, we determined that higher levels of Skp2 are present more frequently in ER-negative tumors than in ER-positive cases. Interestingly, the subset of ER-negative breast carcinomas overexpressing Skp2 are also characterized by high tumor grade, negativity for Her-2, basal-like phenotype, high expression of certain cell cycle regulatory genes, and low levels of p27 protein. We also found that Skp2 expression is cell adhesion-dependent in normal human mammary epithelial cells but not in breast cancer cells and that an inhibition of Skp2 induces a decrease of adhesion-independent growth in both ER-positive and ER-negative cancer cells. Finally, forced expression of Skp2 abolished effects of antiestrogens, suggesting that deregulated Skp2 expression might play a role in the development of resistance to antiestrogens. We conclude that Skp2 has oncogenic potential in breast epithelial cells and is overexpressed in a subset of breast carcinomas (ER- and Her-2 negative) for which Skp2 inhibitors may represent a valid therapeutic option

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Colony-stimulating factor 1 (CSF-1) is an important physiological chemoattractant for macrophages. The mechanisms by which CSF-1 elicits the formation of filamentous actin (F-actin)-rich membrane protrusions and induces macrophage migration are not fully understood. In particular, very little is known regarding the contribution of the different members of the Wiskott-Aldrich Syndrome protein (WASP) family of actin regulators in response to CSF-1. Although a role for WASP itself in macrophage chemotaxis has been previously identified, no data was available regarding the function of WASP family verprolin-homologous (WAVE) proteins in this cell type. We found that WAVE2 was the predominant isoform to be expressed in primary macrophages and in cells derived from the murine monocyte/macrophage RAW264.7 cell line (RAW/LR5). CSF-1 treatment of macrophages resulted in WAVE2 accumulation in F-actin-rich protrusions induced by CSF-1. Inhibition of WAVE2 function by expressing a dominant-negative mutant or introducing anti-WAVE2 antibodies in RAW/LR5 cells, as well as reduction of endogenous WAVE2 expression by RNA-mediated interference (RNAi), resulted in a significant reduction of CSF-1-elicited F-actin protrusions. WAVE2 was found in a protein complex together with Abelson kinase interactor 1 (Abi1) in resting or stimulated cells. Both WAVE2 and Abi1 were recruited to and necessary for the formation of F-actin protrusions in response to CSF-1. Reducing the levels of WAVE2, directly or by targeting Abi1, resulted in an impaired cell migration to CSF-1. Altogether these data identify a WAVE2-Abi1 complex crucial for the normal actin cytoskeleton reorganization and migration of macrophages in response to CSF-1.