2. Introduction
• The Ca2+ ATPases of the plasma
membrane (PMCA pumps)
cooperates with other transport
systems and with soluble
Ca2+binding proteins in the
control of the cellular homeostasis
of Ca2+.
• In mammals they are the products
of four separate genes.
• The PMCAs are classical P-type
pumps.
• PMCAs are regulated by
calmodulin .
• Genetic defects of PMCA
function produce disease
phenotypes.
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Plasma Membrane Calcium ATPases (PMCAs)
3. The Ca2+ channel :
▪ The Ca2+ channels located in the plasma membrane and in the membranes of
the endo(sarco) plasmic reticulum , the Golgi vesicles, the lysosomes .
▪ The Ca2+ pumps (in the reticulum, in the Golgi vesicles and in the plasma
membrane) and the Na+/Ca2+ exchanger of the plasma membrane instead
extract Ca2+ from the cytosol and eject it to the external medium or to the
lumen of the organelles.
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4. General information on the
plasma
membrane Ca2+ pumps
▪ The PMCA pumps belong to the superfamily of P-
type pumps,
▪ They conserve temporarily the energy of the ATP
▪ They have hydrolyzed in a phosphorylated aspartic
acid residue.
▪ The superfamily now contains hundreds of members
divided into eight sub-families.
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5. General information on the plasma membrane Ca2+ pumps
The E1 and E2 (conformational)
states, having different affinities for the transported
species.
In the E1 state the pumps would engage the
transported species with high affinity at the cytosolic
side of the membrane;
In the E2 state the affinity of the enzyme for the
species would decrease substantially, leading to its
release to the external medium of the cell or to the
lumen of the organelles .
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7. Structure, isoforms and regulation of
the PMCA pump
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• For instance, it contains a ~40 residues domain in the cytosolic loop protruding between
transmembrane domains 2 and 3, which binds activatory acidic phospholipids .
• It has a long (~120 residues) tail that emerges from transmembrane domain 10 which contains
the domain that binds the natural activator of the pump, calmodulin .
• The role of calmodulin will then be to remove the C-terminal sequence from the inhibitory sites,
restoring full pump activity.
• In mammals, four genes encode four basic PMCA pumps: isoforms 1 and 4 are widely distributed
in tissues
As for PMCA1, it is expressed in the tissues of the embryo from the earliest times of development.
However, its expression is regulated by a number of factors
8. Structure, isoforms and
regulation of the PMCA pump
▪ At variance with PMCA types 1
and 4, PMCA types 2 and 3 are
expressed in a very limited
number of tissues, the most
important being the nervous
system (the mammary gland also
expresses significant amounts of
PMCA2, and skeletal muscles
PMCA3) .
▪ It interacts with an amphipathic
helical domain in the cytosolic C-
terminal tail, which interacts with
calmodulin with very high affinity.
▪ PMCA2 isoform has high activity in the
absence of calmodulin and is activated
only little by it
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9. The PMCA pumps in disease .
01 PMCA1
02 PMCA2
03 PMCA3
04 PMCA4
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10. PMCA1
▪ The distribution of PMCA1 is ubiquitous .
▪ The ablation of the PMCA1 gene results in early embryonic lethality in homozygotes.
▪ In Asian populations have found a correlation between the locus of the PMCA1 gene and human
systolic blood pressure and coronary artery disease
▪ The relationship between the PMCA1 pump and hypertension.
▪ The PMCA1 isoform could thus have a role in the regulation of blood pressure through the
alteration of Ca2+ handling and vasoconstriction in vascular smooth muscle cells.
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11. PMCA2
▪ The PMCA2 pump is thus the critical actor both in regulating the open probability
of the MET channels and in the maintenance of Ca2+ homeostasis in
the endolymph.
▪ Loss of function of PMCA2 results in deafness
▪ G283S mutation in the first intracellular loop of thePMCA2 pump was predicted to
reduce the activity of the wild-type PMCA2 pump by about 70%
▪ The PMCA2 pump is thus critical for both hearing and balance, reflecting its high
expression in the cerebellum
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MET: mechanoelectrical transduction
The cerebellum (“little brain”) is a structure that is located at the
back of the brain
12. PMCA3
▪ The tissue distribution of the PMCA3 gene product is essentially restricted to the
nervous system
▪ High levels of PMCA3 are associated with the axon terminals of granule cells
▪ The mutation reduces the ability of the PMCA3 pump to control the cellular
homeostasis of Ca2
▪ Recently, using X-exome sequencing a missense mutation (G1107D) has been
identified in the calmodulin binding domain of the PMCA3 Pump in a family with
X-linked congenital cerebellar ataxi
▪ A missense T/M substitution in the PMCA3 pump has recently been identified in
human pancreatic cancer cells.
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13. ▪ PMCA4 isoform is not tissue
restricted
▪ It produces specific
phenotypes, among them male
sterility, which is due to
reduced sperm motility
PMCA4
▪ The PMCA4 pump acts as a
regulator of the activity of
neuronal nitric oxide synthase
(nNOS)
▪ Study on an African
population has revealed an
association between
the locus of the PMCA4 gene
and resistance to malaria
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14. PMCA and cancer
▪ The PMCA2 and PMCA4 pumps are overexpressed in breast cancer cell
lines.
▪ It has recently been shown that the disruption of the PMCA2/calcineurin
interaction in a variety of human breast cancer cells results in the activation
of the calcineurin/NFAT pathway and in the reduction of cell viability, as a
consequence of increased cell apoptosis.
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15. Do you have any question?
Thanks for your
Attention.
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