Figure 6.

S100A1 interacts with SERCA2 and increases activity of the SR Ca²⁺ pump in COS cells. (A) Representative Western blots given for adenovirally expressed S100A1 and SERCA2 in COS cells. β-Actin staining served as loading control. (B) Left: Enhanced Ca²⁺-dependent ATPase activity in SERCA2-expressing COS cells by coexpressed S100A1 protein. Expression of S100A1 alone did not alter Ca²⁺-dependent ATPase activity in COS cells. Note that addition of anti-S100A1 antibody abrogated the S100A1-mediated increase in Ca²⁺-dependent ATPase activity. Right: Increased Ca²⁺-dependent ATPase activity in SERCA2-expressing COS cells following application of human recombinant S100A1 protein (rh-S100A1, 1 μM). Application of anti-S100A1 antibody (10μl) abrogated the S100A1-mediated enhancement of Ca²⁺-dependent ATPase activity. Application of the SERCA2 inhibitor thapsigargin (10^_6 M) abolished Ca²⁺-dependent ATPase activity in AdSERCA2-infected COS cells. Experiments were carried out at pCa 6.2 (n = 3). *P < 0.01 vs. AdSERCA2; **P < 0.01 vs. AdS100A1/AdSERCA2. Data are presented as mean ± SEM. (C) Ca²⁺-dependent coimmunoprecipitation of SERCA2 (red) and S100A1 (green). Samples were immunoprecipated with anti-S100A1 antibody and costained for SERCA2. Control experiments were carried out with an anti-S100A1 antibody preincubated with a blocking peptide.