MMTV promoter-regulated caveolin-1 overexpression yields defective parenchymal epithelia in multiple exocrine organs of transgenic mice

Caveolin-1 (Cav-1) is a major structural protein of caveolae, specialized plasma membrane invaginations that are involved in a cell-specific fashion in diverse cell activities such as molecular transport, cell adhesion, and signal transduction. In normal adult mammals, Cav-1 expression is abundant in mesenchyme-derived cells but relatively low in epithelial parenchyma. However, epithelial Cav-1 overexpression is associated with development and/or progression of many carcinomas. In this study, we generated and characterized a transgenic mouse model of Cav-1 overexpression under the control of a mouse mammary tumor virus (MMTV) long terminal-repeat promoter, which is predominantly expressed in specific epithelial cells. The MMTVcav-1⁺ transgenic mice were fertile, and females bore litters of normal size with no obvious developmental abnormalities. However, by age 11 months, the MMTVcav-1⁺ mice demonstrated overtly different phenotypes in multiple exocrine organs when compared with their nontransgenic MMTVcav-1⁻ littermates. Cav-1 overexpression in MMTVcav-1⁺ mice produced organ-specific abnormalities, including hypotrophy of mammary glandular epithelia, bronchiolar epithelial hyperplasia and atypia, mucous-cell hyperplasia in salivary glands, elongated hair follicles and dermal thickening in the skin, and reduced accumulation of enzymogen granules in pancreatic acinar cells. In addition, the MMTVcav-1⁺ transgenic mice tended to have a greater incidence of malignant tumors, including lung and liver carcinomas and lymphoma, than their MMTVcav-1⁻ littermates. Our results indicate that Cav-1 overexpression causes organ-specific, age-related epithelial disorders and suggest the potential for increased susceptibility to carcinogenesis.