Deficiency of the p53/p63 target Perp alters mammary gland homeostasis and promotes cancer.

INTRODUCTION: Perp is a transcriptional target of both p53 during DNA damage-induced apoptosis and p63 during stratified epithelial development. Perp-/- mice exhibit postnatal lethality associated with dramatic blistering of the epidermis and oral mucosa, reflecting a critical role in desmosome-mediated intercellular adhesion in keratinocytes. However, the role of Perp in tissue homeostasis in other p63-dependent stratified epithelial tissues is poorly understood. Given that p63 is essential for proper mammary gland development and that cell adhesion is fundamental for ensuring the proper architecture and function of the mammary epithelium, here we investigate Perp function in the mammary gland. METHODS: Immunofluorescence and Western blot analysis were performed to characterize Perp expression and localization in the mouse mammary epithelium throughout development. The consequences of Perp deficiency for mammary epithelial development and homeostasis were examined by using in vivo mammary transplant assays. Perp protein levels in a variety of human breast cancer cell lines were compared with those in untransformed cells with Western blot analysis. The role of Perp in mouse mammary tumorigenesis was investigated by aging cohorts of K14-Cre/+;p53fl/fl mice that were wild-type or deficient for Perp. Mammary tumor latency was analyzed, and tumor-free survival was assessed using Kaplan-Meier analysis. RESULTS: We show that Perp protein is expressed in the mammary epithelium, where it colocalizes with desmosomes. Interestingly, although altering desmosomes through genetic inactivation of Perp does not dramatically impair mammary gland ductal development, Perp loss affects mammary epithelial homeostasis by causing the accumulation of inflammatory cells around mature mammary epithelium. Moreover, we show reduced Perp expression in many human breast cancer cell lines compared with untransformed cells. Importantly, Perp deficiency also promotes the development of mouse mammary cancer. CONCLUSIONS: Together, these observations demonstrate an important role for Perp in normal mammary tissue function and in mammary cancer suppression. In addition, our findings highlight the importance of desmosomes in cancer suppression and suggest the merit of evaluating Perp as a potential prognostic indicator or molecular target in breast cancer therapy.

Unimpaired skin carcinogenesis in Desmoglein 3 knockout mice.

The contribution of adherens junction inactivation, typically by downregulation or mutation of the transmembrane core component E-cadherin, to cancer progression is well recognized. In contrast, the role of the desmosomal cadherin components of the related cell-cell adhesion junction, the desmosome, in cancer development has not been well explored. Here, we use mouse models to probe the functional role of desmosomal cadherins in carcinogenesis. Because mice lacking the desmosomal cadherin Desmoglein 3 (Dsg3) have revealed a crucial role for Dsg3 in cell-cell adhesion in stratified epithelia, we investigate the consequence of Dsg3 loss in two models of skin carcinogenesis. First, using Dsg3-/- keratinocytes, we show that these cells display adhesion defects in vitro and compromised tumor growth in allograft assays, suggesting that Dsg3 enables tumor formation in certain settings. In contrast, using an autochthonous model for SCC development in response to chronic UVB treatment, we discover a surprising lack of enhanced tumorigenesis in Dsg3-/- mice relative to controls, unlike mice lacking the desmosomal component Perp. Accordingly, there is no defect in the apoptotic response to UVB or enhanced immune cell infiltration upon Dsg3 loss that could promote tumorigenesis. Thus, Dsg3 does not display a clear function as a tumor suppressor in these mouse skin cancer models. Continued unraveling of the roles of Dsg3 and other desmosomal constituents in carcinogenesis in different contexts will be important for ultimately improving cancer diagnosis, prognostication, and treatment.

Estrogen receptor alpha and the activating protein-1 complex cooperate during insulin-like growth factor-I-induced transcriptional activation of the pS2/TFF1 gene.

Insulin like growth factor I (IGF-I) displays estrogenic activity in breast cancer cells. This activity is strictly dependent on the presence of estrogen receptor alpha (ERalpha). However the precise molecular mechanisms involved in this process are still unclear. IGF-I treatment induces phosphorylation of the AF1 domain of ERalpha and activation of estrogen regulated genes. These genes are characterized by important differences in promoter architecture and response element composition. We show that promoter structure is crucial for IGF-I-induced transcription activation. We demonstrate that on a complex promoter such as the pS2/TFF1 promoter, which contains binding sites for ERalpha and for the activating protein-1 (AP1) complex, transcriptional activation by IGF-I requires both ERalpha and the AP1 complex. IGF-I is unable to stimulate transcription of an estrogen-regulated gene under the control of a minimal promoter containing only a binding site for ERalpha. We propose a molecular mechanism with stepwise assembly of the AP1 complex and ERalpha during transcription activation of pS2/TFF1 by IGF-I. IGF-I stimulation induces rapid phosphorylation and an increase in protein levels of the AP1 complex. Binding of the phosphorylated AP1 complex to the pS2/TFF1 promoter allows recruitment of the chromatin remodeling factor Brg1 followed by binding of ERalpha via its interaction with c-Jun.