|Prapong, Siriwan - IOWA STATE UNIV., AMES|
Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: April 16, 2000
Publication Date: N/A
Technical Abstract: Plasma membrane Ca2+-ATPases (PMCAs) and the putative secretory pathway Ca2+-ATPase (SPCA) are expressed at high levels (mRNA and protein) in lactating mammary tissue. Therefore, the subcellular location of the PMCAs (apical vs. basolateral) and the cellular location of SPCA needs to be established in order to understand the functions of these Ca2+-ATPases in lactating cells. We used immunohistochemistry to define the subcellular localization of these proteins in lactating mammary tissue. Antibody 5F10, which recognizes all PMCA isoforms, detected PMCA expression on both the apical and basolateral membrane of mammary alveolar epithelium. In contrast, isoform-specific antibodies showed that PMCA2 and PMCA4 are primarily localized on the apical membrane of the alveolar epithelium. Apical localization of PMCA2 and PMCA4 indicates that these Ca2+-ATPases function in transporting calcium from the cell to the milk compartment. The SPCA protein was found in an intracellular compartment of the alveolar epithelium in a region of the cytoplasm adjacent to the nucleus. The localization of SPCA in this region of the cell suggests that SPCA may be located in the Golgi. The intracellular location of SPCA suggests that SPCA may be a candidate for the Golgi Ca2+-ATPase involved in maintaining Golgi calcium concentrations required for casein micelle formation. The results from these experiments enable us to define the significance and the relationship between the expression of each PMCA isoform and the transcellular Ca2+ movement in the mammary tissue.