Modification and repression of genes expressed in the mammary gland using gene targeting and other technologies

Bovine lactoferrin binds to insulin-like growth factor-binding protein-3

Insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) has been shown to have IGF independent actions that appear to be mediated by specific IGFBP-3 binding proteins located on cell membranes. We show here using Western ligand blotting, a number of mammary membrane proteins that bind 125I-labeled rhIGFBP-3. Immunoprecipitation studies demonstrated that the >70 kDa protein was identified from bovine mammary microsomes as bovine lactoferrin (bLf). In addition to being a secretory protein, Lf is tightly associated with cellular membranes. Labeled rhIGFBP-3 was shown to bind to commercially purchased and processed apo- or holo-human or bLf, but not bovine transferrin (bTf). Binding of [125I]rhIGFBP-3 to other positively charged proteins was not detected nor was binding to rhIGFBP-5 or other mammary-secreted IGFBPs observed. Reciprocal specific binding of [125I]bLf to rhIGFBP-3 was shown, but [125I]bTf did not show binding to rhIGFBP-3. While [125I]rhIGF-II does not bind to bLf, unlabeled rhIGF-II was shown to compete with [125I]bLf for rhIGFBP-3 binding. More detailed analysis by dot blot showed that Lf competes (ED(50)=3 microg/ml) or displaces (ED(50)=1mg/ml) bound [125I]rhIGF-II from dot blotted rhIGFBP-3. In vitro studies with a bovine primary mammary epithelial cell culture showed that all-trans-retinoic acid stimulates the appearance of bovine IGFBP-3 and bLf in the conditioned media and that [125I]rhIGFBP-3 could be utilized to detect conditioned media bLf. These findings reveal a novel role for bLf, binding to IGFBP-3 and perhaps disassociating IGFBP-3:IGF when in high concentration.

Cellular turnover in the mammary gland is correlated with systemic levels of progesterone and not 17beta-estradiol during the estrous cycle

Adult mammary tissue has been considered "resting" with minimal morphological change. Here, we reveal the dynamic nature of the nulliparous murine mammary gland. We demonstrate specific changes at the morphological and cellular levels, and uncover their relationship with the murine estrous cycle and physiological levels of steroid hormones. Differences in the numbers of higher-order epithelial branches and alveolar development led to extensive mouse-to-mouse mammary variations. Morphology (assigned grades 0-3) ranged from a complete lack of alveoli to the presence of numerous alveoli emanating from branches. Morphological changes were driven by epithelial proliferation and apoptosis, which differed between ductal versus alveolar structures. Proliferation within alveolar epithelium increased as morphological grade increased. Extensive alveolar apoptosis was restricted to tissue exhibiting grade 3 morphology, and was approximately 14-fold higher than at all other grades. Epithelial proliferation and apoptosis exhibited a positive relationship with serum levels of progesterone, but not with 17beta-estradiol. Compared with other estrous stages, diestrus was unique in that the morphological grade, epithelial proliferation, apoptosis, and progesterone levels all peaked at this stage. The regulated tissue remodeling of the mammary gland was orchestrated with mRNA changes in specific matrix metalloproteinases (MMP-9 and MMP-13) and specific tissue inhibitors of metalloproteinases (TIMP-3 and TIMP-4). We propose that the cyclical turnover of epithelial cells within the adult mammary tissue is a sum of spatial and functional coordination of hormonal and matrix regulatory factors.