ARS | Publication request: CA2+ ATPASE PROTEIN EXPRESSION IN MAMMARY TISSUE: ALTERNATE SPLICING AND SECRETION OF PLASMA MEMBRANE CA2+ ATPASE 2B

Submitted to: American Society of Cell Biology Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 12, 1999
Publication Date: N/A

Technical Abstract: We investigated plasma membrane Ca2+ ATPase (PMCA) and the putative Golgi secretory pathway Ca2+ ATPase (SPCA) protein expression in the developing and lactating mammary gland. Using a general PMCA antibody, we found little PMCA in mammary tissue prior to parturition. As lactation started, PMCA expression increased and this increase paralleled milk production. Isoform-specific antibodies showed that PMCA2b was the primary PMCA present, but ca. 4000 daltons larger than expected. RT-PCR showed that the PMCA2b transcript was alternatively spliced to include an additional 135 bp resulting in the insertion of 45 amino acids. This splice form is designated 2bw and accounts for the 4000 dalton increase in PMCA2b's size. PMCA2bw was secreted into milk, associated with the milk fat globule membrane, thus demonstrating that PMCA2bw is located on the apical membrane of the secretory cell. Small amounts of PMCA1b and 4b protein were found in lactating tissue. PMCA4b was expressed in developing mammary tissue and declined during lactation. PMCA1b increased moderately during lactation. PMCA2bw expression rose only after lactation started, whereas SPCA expression increased prior to parturition and increased further as lactation proceeded. PMCA2b's abundance, cell location, high affinity for Ca2+, and high constitutive activity suggests that PMCA2b is important for macro-Ca2+ homeostasis in lactating tissue. SPCA's pattern of expression and abundance suggest that SPCA is a candidate for the Golgi Ca2+ ATPase shown to be important in maintaining Golgi Ca2+ concentration required for casein synthesis.