Consequences of Functional Expression of the Plasma Membrane Ca2+ Pump Isoform 1a

Abstract

The plasma membrane Ca 2؉ -ATPase pump (PMCA) is an integral component of the Ca 2؉ signaling system which participates in signal transduction during agonist stimulated cell activation. To better understand the physiological function of the pump, isoform 1a (PMCA1a) was over-expressed in rat aortic endothelial cells using a stable transfection system under the control of a cytomegalovirus promoter. The cell lines selected after transfection with PMCA1a construct, expressed 3-4-fold increased pump protein which was mostly targeted to the plasma membrane as indicated by immunoperoxidase staining. Ca 2؉ uptake assays in a membrane preparation indicated a 3-4-fold increase in Ca 2؉ pumping activity in the transfected cells, and the expressed PMCA1a showed typical dependence on Ca ] i evoked by ATP and/or thapsigargin was lower but the plateau phase was similar in the PMCA1a expressing cells.

Plasma Membrane Ca2+-ATPase Overexpression Reduces Ca2+ Oscillations and Increases Insulin Release Induced by Glucose in Insulin-Secreting BRIN-BD11 Cells

“…The overexpressed protein was appropriately targeted to the plasma membrane, as shown by immunofluorescence and the increase in ATP-dependent 45 Ca uptake observed in plasma membrane microsomes. As expected for PMCA-mediated Ca 2ϩ transport, 45 Ca uptake was regulated by the Ca 2ϩ concentration in the assay medium within the submicromolar range and by calmodulin without changing the sensitivity to ambient Ca 2ϩ (41 (Fig. 6A).…”

Isoform-specific up-regulation of plasma membrane Ca2+ATPase expression during colon and gastric cancer cell differentiation

“…PMCA4b may therefore confer specific kinetic characteristics to a Ca 2+ transient. Because of the difficulties encountered during the cloning and expression of PMCA1 cDNA [13,14], biochemical data are fairly limited for this PMCA pump. Thus, it is currently difficult to hypothesize how PMCA1 shapes the Ca 2+ transients during signaling events.…”

“…Biochemically, PMCA4b is characterized by: i) low basal activity in the absence of calmodulin; ii) slow activation by the Ca 2+ -calmodulin complex and iii) slow inactivation of the calmodulin-activated pump [10][11][12]. For PMCA1 biochemical data are limited due to the difficulties encountered during the cloning and expression of its cDNA [13,14]. The affinity of PMCA1 for calmodulin appeared to be similar to that of PMCA4, but it has higher affinity for ATP and a higher susceptibility to degradation by calpain [15].…”

Plasma membrane calcium ATPases as critical regulators of calcium homeostasis during neuronal cell function

“…In contrast to the PMCA1-deficient PC6 cells which showed no change in [Ca 2+ ] i , the hPMCA4b-overexpressing L6 cells displayed a significant (20-30%) reduction of the resting [Ca 2+ ] i . However, this may be unique to this cell system, as overexpression (by 3-4 fold) of PMCA1a in rat aortic endothelial cells did not alter basal [Ca 2+ ] i in these cells (62). Similarly, we have recently investigated stably transfected PC12 cells that either overexpressed exogenous hPMCA4b or were deficient in their endogenous PMCA4 (63).…”

“…For example, overexpression of exogenous PMCA1a in rat aortic endothelial cells, or of PMCA4b in Chinese hamster ovary cells leads to compensatory changes (i.e., a downregulation) of the cells' endogenous SERCA pumps (62,64,65). An important signal that induces changes in PMCA expression and is involved in neuronal (and non-neuronal) differentiation is Ca …”