Comparative Proteomic Analysis of Models of Mammary Cell Differentiation

Mammary development is a process driven by endocrine signals and involving complex, coordinated intracellular alterations.  While endocrine signals involved in the conversion of mammary precursor cells to functional mammary epithelial cells (MEC) are well understood, the intracellular events and their regulation remain unresolved.  Comparative analysis of the changes in molecular phenotype between mammary precursor and functional MEC among different species may aid in elucidating the key regulatory events in MEC differentiation.  We used 2DGE and MALDI-TOF MS/MS to compare shifts in the proteome during differentiation of a normal mammary epithelial cell line of murine origin (HC11) to one of bovine origin (MAC-T) and primary murine MEC.  After culture with lactogenic hormones we identified 75 (HC11) and 48 (MAC-T) differentially expressed proteins, while comparison of mammary cells isolated from pregnant and lactating mice revealed 68 differentially expressed proteins.  HC11 exhibited up-regulation of metabolic and RNA processing proteins, and down-regulation of proteins involved in cell proliferation and protein synthesis and folding. Proteome changes in HC11 were strikingly different in all major functional categories from those observed in the MAC-T.  HC11 cells and Primary MEC exhibited similar changes in proteins involved in metabolism and protein synthesis and folding, but opposite regulation of RNA processing and cytoskeletal proteins.  This analysis distinguishes aspects of MEC differentiation for which cell lines may or may not be appropriate models and indicates the importance of comparative analysis among species and models to reveal commonalities, which may be important for identifying central regulatory networks.