Phospholamban Antibody

8495:

Western Blotting

Phospholamban Antibody recognizes endogenous levels of total phospholamban protein.

Polyclonal antibodies are produced by immunizing animals with a synthetic peptide corresponding to residues near the amino terminus of human phospholamban protein. The peptide does not overlap Ser16 and Thr17. Antibodies are purified by protein A and peptide affinity chromatography.

Western Blotting

Western blot analysis of extracts from 16-month old control (WKY) and spontaneous hypertensive (SHR) rat hearts using Phospho-Phospholamban (Ser16/Thr17) Antibody #8496 (left), Phospholamban Antibody (middle), or GAPDH (14C10) Rabbit mAb #2118 (right).

Phospholamban (PLN) was identified as a major phosphoprotein component of the sarcoplasmic reticulum (SR) (1). Its name, "lamban", is derived from the greek word "lambano" meaning "to receive", so named due to the fact that phospholamban is heavily phosphorylated on serine and threonine residues in response to cardiac stimulation (1). Although originally thought to be a single 20-25 kDa protein due to its electrophoretic mobility on SDS-PAGE, PLN is actually a 52 amino acid, 6 kDa, membrane-spanning protein capable of forming stable homooligomers, even in the presence of SDS (2). Despite very high expression in cardiac tissue, phospholamban is also expressed in skeletal and smooth muscle (3). Localization of PLN is limited to the SR, where it serves as a regulator of the sarco-endoplasmic reticulum calcium ATPase, SERCA (4). PLN binds directly to SERCA and effectively lowers its affinity for calcium, thus reducing calcium transport into the SR. Phosphorylation of PLN at Ser16 by Protein Kinase A or myotonic dystrophy protein kinase and/or phosphorylation at Thr17 by Ca²⁺ /calmodulin-dependent protein kinase results in release of PLN from SERCA, relief of this inhibition, and increased calcium uptake by the SR (reviewed in 5,6). It has long been held that phosphorylation at Ser16 and Thr17 occurs sequentially, but increasing evidence suggests that phosphorylation, especially at Thr17, may be differentially regulated (reviewed in 7,8).Rodent models of heart failure have shown that the expression level and degree of phosphorylation of PLN are critical in modulating calcium flux and contractility (reviewed in 9-11). Deletion or decreased expression of PLN promotes increased calcium flux and increased cardiac contractility, whereas overexpression of PLN results in sequestration of SERCA, decreased calcium flux, reduced contractility, and rescue of cardiac dysfunction and failure in mouse models of hypertension and cardiomyopathy (reviewed in 10). Distinct mutations in PLN have been detected in humans, resulting either in decreased or no expression of PLN protein (12,13) or binding defects between PLN, SERCA and/or regulatory proteins (14,15), both of which result in cardiac myopathy and heart failure. Interestingly, while the human phenotype of most PLN defects mimic those seen in rodent and vice versa, there are some instances where the type and severity of cardiac disease resulting from PLN mutations in rodent and human differ, making a consensus mechanism elusive.

1. Kirchberber, M.A. et al. (1975) Recent Adv Stud Cardiac Struct Metab 5, 103-15.
2. Zhan, Q.Q. et al. (1991) J Biol Chem 266, 21810-4.
3. Fujii, J. et al. (1991) J Biol Chem 266, 11669-75.
4. Tada, M. and Kirchberger, M.A. Recent Adv Stud Cardiac Struct Metab 11, 265-72.
5. Traaseth, N.J. et al. (2008) Biochemistry 47, 3-13.
6. Bhupathy, P. et al. (2007) J Mol Cell Cardiol 42, 903-11.
7. Hagemann, D. and Xiao, R.P. (2002) Trends Cardiovasc Med 12, 51-6.
8. Mattiazzi, A. et al. (2005) Cardiovasc Res 68, 366-75.
9. Chu, G. and Kranias, E.G. (2006) Novartis Found Symp 274, 156-71; discussion 172-5, 272-6.
10. Schwinger, R.H. and Frank, K.F. (2003) Sci STKE 2003, pe15.
11. MacLennan, D.H. and Kranias, E.G. (2003) Nat Rev Mol Cell Biol 4, 566-77.
12. Haghighi, K. et al. (2008) Hum Mutat 29, 640-7.
13. Haghighi, K. et al. (2003) J Clin Invest 111, 869-76.
14. Schmitt, J.P. et al. (2003) Science 299, 1410-3.
15. Haghighi, K. et al. (2006) Proc Natl Acad Sci USA 103, 1388-93.

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