Proteomic analysis of two functional states of the Golgi complex in mammary epithelial cells

Organellar compartments involved in secretion are expanded during the trans ition from late pregnancy (basal secretory state) to lactation (maximal sec retory state) to accommodate for the increased secretory function required for copious milk production in mammary epithelial cells. The Golgi complex is a major organelle of the secretory pathway and functions to sort, packag e, distribute, and post-translationally modify newly synthesized proteins a nd membrane lipids. These complex functions of the Golgi are reflected in t he protein complement of the organelle. Therefore, using proteomics, the pr otein complements of Golgi fractions isolated at two functional states (bas al and maximal) were compared to identify some of the molecular changes tha t occur during this transition. This global analysis has revealed that only a subset of the total proteins is upregulated from steady state during the transition. Identification of these proteins by tandem mass spectrometry h as revealed several classes of proteins involved in the regulation of membr ane fusion and secretion. This first installment of the functional proteomi c analysis of the Golgi complex begins to define the molecular basis for th e transition from basal to maximal secretion.