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A comparative functional analysis of plasma membrane Ca2+ pump isoforms in intact cells
Marisa Brini1, Luisa Coletto, Nicola Pierobon
1Department of Biochemistry and Center for the Study of Biomembranes of the National Research Council (CNR), University of Padova, Viale G. Colombo 3, Italy. marisa.brini@unipd.it
The Journal of Biological Chemistry
|April 30, 2003
Summary
Plasma membrane calcium ATPases (PMCAs) regulate intracellular calcium. Both full-length and truncated PMCA variants effectively control cellular calcium levels, suggesting calmodulin availability is not critical for PMCA pump modulation.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Physiology
Background:
- Plasma membrane Ca2+ ATPases (PMCAs) are crucial for maintaining calcium homeostasis.
- Specific PMCA isoforms and their spliced variants exhibit distinct properties and cellular roles.
- Understanding the functional impact of truncated PMCA variants on calcium regulation is essential.
Purpose of the Study:
- To investigate the functional roles of four basic PMCA isoforms and two C-terminally truncated variants (PMCA4CII(4a) and PMCA3CII(3a)) in cellular calcium handling.
- To clone, purify, and characterize the previously unstudied PMCA3CII(3a) variant.
- To compare the efficacy of full-length and truncated PMCA variants in modulating intracellular calcium levels.
Main Methods:
- Transient overexpression of PMCA isoforms and variants in Chinese hamster ovary (CHO) cells.
- Co-expression with aequorin targeted to cytosol, endoplasmic reticulum, and mitochondria.
- Cloning, partial purification, and characterization of the PMCA3CII(3a) variant.
- Measurement of intracellular calcium ([Ca2+]) levels and transients.
Main Results:
- Overexpression of all four basic PMCA pump variants affected intracellular calcium homeostasis.
- PMCA pump overexpression reduced endoplasmic reticulum [Ca2+] and cytosolic/mitochondrial [Ca2+] transients.
- Neuron-specific PMCA2 and PMCA3 showed more pronounced effects than ubiquitous isoforms 1 and 4.
- Truncated PMCA3 and PMCA4 variants were as effective as full-length versions in regulating organelle and cytosolic calcium.
- PMCA4CII(4a) demonstrated efficacy comparable to PMCA4CI(4b) despite lower calmodulin affinity.
Conclusions:
- Both full-length and truncated PMCA variants significantly influence cellular calcium homeostasis.
- The functional impact of PMCA pumps on calcium regulation in cytosol and organelles is independent of their truncation status.
- Calmodulin availability may not be a critical factor for modulating PMCA pump activity in vivo.