Submitted to: Federation of American Societies for Experimental Biology Conference
Publication Type: Abstract Only
Publication Acceptance Date: April 21, 2002
Publication Date: N/A
Technical Abstract: The rat alternatively-spliced mRNA (accession #M93017) has been suggested to be a Golgi secretory pathway Ca2+-ATPase (SPCA) based on sequence similarities to the yeast PMR-1 gene. Sucrose gradient fractionation of rat liver microsomes resulted in SPCA co-migrating with the Golgi calcium binding protein CALNUC which was well resolved from the ER marker calreticulin. In addition, antibody to SPCA co-localized in PC-12 cells with an antibody to the Golgi marker mannosidase II. Stable over- expression of SPCA resulted in a significant reduction of plasma membrane Ca2+-ATPase and calreticulin expression in these clones. In contrast, the expression of the Golgi calcium binding protein CALNUC increased significantly. In the remaining experiments, the SPCA clone G11/5 was used. The phosphoenzyme intermediate formed, using membranes from clone G11/5, was calcium-dependent and significantly more intense than in COS-7 cells. Calcium uptake of G11/5 microsomes was ATP-dependent and significantly greater than in microsomes from parent COS-7 cells. Interestingly, the over-expression of SPCA shortened the generation time of COS-7 cells from approx. 48 h to only approx. 16 h in the COS-7 clone G11/5. These data demonstrate that the rat alternatively-spliced mRNA (accession #M93017) is a Golgi Ca2+-ATPase.