Role of regucalcin as an activator of Ca2+-ATPase activity in rat liver microsomes

Abstract

The effect of Ca(2+)-binding protein regucalcin on Ca(2+)-ATPase activity in isolated rat liver microsomes was investigated. The presence of regucalcin (0.1-1.0 microM) in the enzyme reaction mixture led to a significant increase in Ca(2+)-ATPase activity. Regucalcin significantly stimulated ATP-dependent (45)Ca(2+) uptake by the microsomes. Thapsigargin (10(-6) M), a specific inhibitor of microsomal Ca(2+) pump enzyme (Ca(2+)-ATPase), clearly inhibited regucalcin (0.5 microM)-increased microsomal Ca(2+)-ATPase activity. Liver microsomal Ca(2+)-ATPase activity was markedly decreased by N-ethylmaleimide (NEM; 2.5 mM), while the activity was clearly elevated by dithiothreitol (DTT; 2.5 mM), indicating that the sulfhydryl (SH) group of the enzyme is an active site. The effect of regucalcin (0.5 microM) in increasing Ca(2+)-ATPase activity was completely inhibited by the presence of NEM (2.5 mM) or digitonin (10(-2) %), a solubilizing reagent of membranous lipids. Moreover, the effect of regucalcin on enzyme activity was seen in the presence of Ca(2+) ionophore (A23187; 10(-7) M). The present study demonstrates that regucalcin can stimulate Ca(2+) pump activity in rat liver microsomes, and that the protein may act the SH groups of microsomal Ca(2+)-ATPase.

Senescence marker protein 30: functional and structural insights to its unknown physiological function

“…Interaction of SMP30 with calmodulin also appears to regulate the activation of survival factor Akt (46). The ability of SMP30 to stimulate membrane Ca 2+ pumps was also demonstrated in vivo using isolated rat liver plasma membranes and microsomes (47, 48). …”

Proteomic Analysis of Membrane-Associated Proteins from Rat Liver Autophagosomes

“…Regucalcin has been shown to stimulate several membrane-bound Ca 2+ pumps, 215 including the microsomal Ca 2+ -ATPase, 220 which is of particular interest in light of the obligatory dependence of autophagic sequestration on intracisternal Ca 2+ . 221 Various hepatocellular enzymatic activities are also stimulated by regucalcin, such as superoxide dismutase 222 and the proteinase calpain, 223 which may be involved in the defense against protein oxidation and the disposal of denatured proteins, respectively.…”

Regucalcin Expression in Bovine Tissues and Its Regulation by Sex Steroid Hormones in Accessory Sex Glands

“…Subsequently, RGN was identified as senescence marker protein-30 (SMP-30) based on the characteristic down-regulation of this protein with ageing in the rat liver [3]. As the name suggests, RGN regulates intracellular Ca 2+ homeostasis through the modulation of the activity of Ca 2+ channels, Ca 2+ -ATPase in the membrane of mitochondria and endoplasmic reticulum [4], [5] and (Ca 2+ -Mg 2+ )-ATPase in the plasma membrane [6], [7]. Moreover, RGN plays an important role in the regulation of Ca 2+ -dependent enzymes, such as protein kinases, tyrosine kinases, phosphatases, phosphodiesterase, nitric oxide synthase and proteases [8]–[13].…”