Disease relevance of Pln

• We conclude that PLB is crucial to the recovery of Delta[Ca]i and k(Ca) during acidosis [1].
• On the other hand, the basal contractile state of wild-type and phospholamban-deficient hearts was significantly increased in hyperthyroidism [2].
• The basal contractile state of wild-type and phospholamban-deficient hearts was significantly depressed in hypothyroidism [2].
• Hypothyroidism was associated with significant decreases in heart/body weight ratio in wild-type and phospholamban-deficient mice, whereas hyperthyroidism was associated with significant increases in heart/body weight ratio in both groups [2].
• Rescue of cardiomyocyte dysfunction by phospholamban ablation does not prevent ventricular failure in genetic hypertrophy [3].

High impact information on Pln

• The ablation of a muscle-specific sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) inhibitor, phospholamban, rescued the spectrum of phenotypes that resemble human heart failure [4].
• Inhibition of phospholamban-SERCA2a interaction via in vivo expression of a phospholamban point mutant dominantly activated the contractility of ventricular muscle cells [4].
• In mice, phospholamban seems to encumber an otherwise healthy heart, but humans with a phospholamban-null genotype develop early-onset dilated cardiomyopathy [5].
• In contrast, phospholamban ablation prevented systolic dysfunction and exercise intolerance, but not hypertrophy, in hypertrophic cardiomyopathy mice [6].
• Interestingly, the proteins involved in the Ca2+-release cascade (ryanodine receptor, junctin, and triadin) were downregulated, whereas Ca2+-uptake proteins (Ca2+-ATPase and phospholamban) were unchanged or slightly increased [7].

Chemical compound and disease context of Pln

• It has therefore been proposed that normalization of sarcoplasmic reticulum Ca(2+) cycling through inhibition or ablation of the Ca(2+) ATP-ase inhibitor phospholamban (PLN), which shows promise as a treatment for heart failure, could be beneficial in ischemic heart disease [8].
• Transfection into the androgen-independent, bone targeted prostate cancer line, C4-2B, and efficient stable knockdown of Pln was demonstrated by quantitative PCR, immunohistochemistry and immunoblotting [9].
• A monoclonal antibody, A1, was produced against sodium dodecyl sulfate-polyacrylamide gel electrophoresis purified canine phospholamban and isolated from mouse ascites by chromatography on a hydroxylapatite column [10].

Biological context of Pln

• Differential phospholamban gene expression in murine cardiac compartments. Molecular and physiological analyses [11].
• Furthermore, the prolongation of muscle relaxation appeared to correlate with the levels of phospholamban expressed in two transgenic mouse lines [12].
• Moreover, PLB phosphorylation by CaMKII plays an important role in limiting the decline in Ca transients (and contraction) during acidosis [1].
• The use of transgenic mice has yielded surprises ,uch as PLB modulation of endothelial cell Ca2+ homeostasis, and the demonstration that PLB is the major site for A-kinase-mediated relaxation of mouse bladder [13].
• A mouse line carrying a transgene for the smooth muscle specific expression of PLB has been reported [13].

Anatomical context of Pln

• Expression of PLB is reportedly limited to cardiac, slow-twitch skeletal and smooth muscle in which PLB is an important regulator of [Ca2+]i and contractility in these muscles [14].
• These findings were corroborated by in situ hybridization studies of cardiopulmonary sections from both murine strains, and phospholamban transcripts were also observed in pulmonary myocardia of both strains [11].
• Phospholamban (PLB) is a 24- to 27-kDa phosphoprotein that modulates activity of the sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) [14].
• The presence of PLB in endothelial cells opens new fields for investigation of Ca2+ regulatory pathways in nonmuscle cells and for modulation of endothelial-vascular interactions [14].
• This effect was not due to actions of nitric oxide on the smooth muscle, because sodium nitroprusside-mediated relaxation in either denuded or endothelium-intact aortas was unaffected by PLB ablation [14].

Associations of Pln with chemical compounds

• Endothelium-dependent relaxation to acetylcholine was attenuated in aorta of PLB-deficient (PLB-KO) mice compared with wild-type (WT) controls [14].
• These measurements were repeated in ventricular myocytes from novel mice with cardiac CaMKII inhibition lacking phospholamban (PLN), a known CaMKII substrate and a negative regulator of Ca(2+)(i) uptake into the SR Ca(2+) store [15].
• Baseline levels of these parameters in the phospholamban-deficient hearts were equal to those observed in hearts of wild-type littermates maximally stimulated with the beta-agonist isoproterenol [16].
• We investigated this by measuring the effects of carbachol (CCh) on force and [Ca2+]i in bladder from mice in which the PLB gene was ablated (PLB-KO mice) [17].
• The CaMKII inhibitor KN-93 inhibited caffeine-induced relaxation and PLB Thr17 phosphorylation [18].

Physical interactions of Pln

• Sarcolipin (SLN) inhibits the cardiac sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA2a) by direct binding and is superinhibitory if it binds as a binary complex with phospholamban (PLN) [19].
• Phospholamban is a regulatory phosphoprotein which modulates the active transport of Ca2+ by the cardiac sarcoplasmic reticular Ca(2+)-ATPase enzyme (SERCA2) into the lumen of the sarcoplasmic reticulum [20].

Enzymatic interactions of Pln

• The pure phospholamban could be phosphorylated maximally by cAMP-dependent protein kinase to 1-1.5 mol phosphate/mol phospholamban (25,000 g) [21].

Regulatory relationships of Pln

• Phospholamban is present in tissues that express the SERCA2 isoform and is an inhibitor of the affinity of SERCA2 for calcium [12].
• In vitro reconstitution and cell culture expression studies have shown that phospholamban can also regulate SERCA1, the fast-twitch skeletal muscle isoform [12].
• Residues 2-25 of phospholamban are insufficient to inhibit Ca2+ transport ATPase of cardiac sarcoplasmic reticulum [22].
• Triton-X skinned fiber preparations from phospholamban deficient (n = 9) and wild-type (n = 10) mice were used and the Ca2+-activated force as well as the myosin ATPase-activity were simultaneously measured [23].
• Purified recombinant Pln induced NO production at low concentrations and independently of exogenous gamma interferon (IFN-gamma) priming of RAW 264.7 macrophages [24].

Other interactions of Pln

• Analyses of phospholamban transcript levels relative to alpha-myosin heavy chain (alpha-MHC) revealed a 3-fold higher phospholamban abundance in the ventricle compared with the atrium of the FVB/N murine strain [11].
• PLB via modulation of SERCA can play a major role in regulation of both phasic and tonic smooth muscle contractility [13].
• Consequently, the relative ratio of phospholamban to SERCA2 mRNA was 4.2-fold lower in the atrium than in the ventricle [11].
• Cardiac-specific overexpression of sarcolipin in phospholamban null mice impairs myocyte function that is restored by phosphorylation [19].
• Expression of additional phospholamban molecules results in: (a) inhibition of SR Ca2+ transport; (b) decreases in systolic Ca2+ levels and contractile parameters in ventricular myocytes; and (c) depression of basal left ventricular systolic function in vivo [25].

Analytical, diagnostic and therapeutic context of Pln

• Both reverse transcriptase-polymerase chain reaction and Western blot analyses revealed the presence of PLB in endothelial cells, which were shown to be >98% pure by diI-acetylated LDL uptake and nuclear counterstaining [14].
• Quantitative immunoblotting revealed a twofold increase in the phospholamban protein levels in transgenic hearts compared to wild type littermate hearts [25].
• Sequence analysis of the cDNA encoding phospholamban in embryoid bodies indicated complete homology to that in adult hearts [26].
• Only those embryoid bodies that exhibited contractions expressed phospholamban transcripts, and these were accompanied by expression of the protein, as revealed by immunofluorescence microscopy [26].
• To assess the regulation of phospholamban gene expression during murine development, Northern blot and polymerase chain reaction analyses were used [26].

References