Disease relevance of PLEK

• A 1,050 base pair (bp) open reading frame that could encode a protein of Mr40,087 was confirmed by comparison with peptide sequences from platelet P47, and by expression of the putative recombinant P47 in E. coli and in vitro [1].
• Dimerization of Cool-2 enables its Dbl (diffuse B-cell lymphoma) and pleckstrin homology domains to work together (in trans) to bind specifically to Rac-GDP [2].
• Evidence that the expression and phosphorylation status of pleckstrin is modulated by Epstein-Barr virus in human B lymphocytes [3].
• We have reported data on a patient with thrombocytopenia and impaired receptor-mediated aggregation, phosphorylation of pleckstrin (a protein kinase C [PKC] substrate), and activation of the GPIIb-IIIa complex [4].
• 3BP2 is a pleckstrin homology domain- and Src homology 2 (SH2) domain-containing adapter protein that is mutated in the rare human bone disorder cherubism and which has also been implicated in immunoreceptor signaling [5].

High impact information on PLEK

• Mutations in the pleckstrin homology domain of dynamin 2 cause dominant intermediate Charcot-Marie-Tooth disease [6].
• The PTB domains of IRS-1 and Shc share a common fold with pleckstrin homology domains [7].
• Crystal structure at 2.2 A resolution of the pleckstrin homology domain from human dynamin [8].
• Pleckstrin, the major protein kinase C substrate of platelets, contains domains of about 100 amino acids at the amino and carboxy termini that have been found in a number of proteins, including serine/threonine kinases, GTPase-activating proteins, phospholipases and cytoskeletal proteins [9].
• Pleckstrin homology domains bind to phosphatidylinositol-4,5-bisphosphate [10].

Chemical compound and disease context of PLEK

• PKD2 was found to be the major isoform of the PKD family expressed in chronic myeloid leukemia cells and is tyrosine phosphorylated by Bcr-Abl in its pleckstrin homology domain [11].
• Utilizing the pleckstrin homology domains of PKC-delta and Btk proteins fused to green fluorescent protein (GFP), which specifically interact with PIP2 and PIP3, respectively, we show herein that E. coli invasion induces the breakdown of PIP2 at the plasma membrane near the site of E. coli interaction [12].
• Alanine substitutions within the pleckstrin homology-like domain of SUS1 reduced membrane association in E. coli and with plant microsomes in vitro without reducing enzymatic activity [13].
• In eclampsia, generation of phosphatidic acid and phosphorylation of pleckstrin were decreased by 25% (P < 0.05, n = 3) and 35% (P < 0.05, n = 3), respectively, after 60 sec of platelet stimulation [14].
• Large-scale expression and purification of a soluble form of the pleckstrin homology domain of the human protooncogenic serine/threonine protein kinase PKB (c-akt) in Escherichia coli [15].

Biological context of PLEK

• Phosphorylation of the PH-DEP linker, which is required for pleckstrin function, could regulate such an intramolecular interaction [16].
• Based on the results of clinical study, we consider that acupuncture analgesic effect on stomach carcinoma is related to the increase of PLEK, improvement of cellular immune function and the elevation of life quality after acupuncture [17].
• The P47 protein contains a potential Ca2+-binding 'EF-hand' structure and a region that strongly resembles known PKC phosphorylation sites [1].
• We have isolated human P47 clones by immunological screening of a lambda gt11 complementary DNA library from HL-60 cells, a human promyelocytic leukaemia cell line [1].
• We have recently shown that pleckstrin can inhibit agonist-induced phosphoinositide hydrolysis and that this inhibition requires an intact N-terminal PH domain (residues 6 to 99) [18].

Anatomical context of PLEK

• Pleckstrin1 is a major substrate for protein kinase C in platelets and leukocytes, and comprises a central DEP (disheveled, Egl-10, pleckstrin) domain, which is flanked by two PH (pleckstrin homology) domains [16].
• In human platelets activated with thrombin or phorbol esters, and in COS-1 cells expressing pleckstrin, a combination of phosphopeptide analysis and site-directed mutagenesis shows that three residues in the intervening sequence between the two pleckstrin PH domains become phosphorylated: Ser113, Thr114, and Ser117 [18].
• Pleckstrin is the major target of protein kinase C (PKC) in blood platelets [19].
• As a probe of intracellular signals responsible for this asymmetry, the pleckstrin homology domain of the AKT protein kinase (or protein kinase B), tagged with the green fluorescent protein (PHAKT-GFP), was expressed in neutrophils [20].
• A gain-of-function mutant called Btk* containing E41 to K change within the pleckstrin homology domain induces fibroblast transformation [21].

Associations of PLEK with chemical compounds

• In platelets, agonists that stimulate phosphoinositide turnover cause the rapid phosphorylation of a protein of apparent relative molecular mass (Mr) 40-47,000, called P47, by protein kinase C (PKC) [1].
• Diverse identities have been ascribed to P47 including lipocortin, inositol 1,4,5-trisphosphate 5-phosphomonoesterase, pyruvate dehydrogenase alpha subunit and an actin regulatory protein [1].
• We now show that pleckstrin in platelets is in a complex with inositol polyphosphate 5-phosphatase I (5-phosphatase I) [22].
• Mutational analysis of the pleckstrin homology domain of the beta-adrenergic receptor kinase. Differential effects on G beta gamma and phosphatidylinositol 4,5-bisphosphate binding [23].
• Replacing the phosphorylation sites with alanine residues had a similar effect, while substitution with aspartate, glutamate, or lysine residues produced pleckstrin variants that were fully active even in the absence of phosphorylation [18].

Physical interactions of PLEK

• The pleckstrin homology and phosphotyrosine binding domains of insulin receptor substrate 1 mediate inhibition of apoptosis by insulin [24].
• AFAP-110 contains additional protein binding modules including two pleckstrin homology domains, a leucine zipper motif and a target sequence for serine/threonine phosphorylation [25].
• The ORP have two major structural features: a highly conserved OSBP-type sterol-binding domain in the C-terminal half and a pleckstrin homology domain present in the N-terminal region of most family members [26].
• All TCL1 isoforms bind to the Akt pleckstrin homology domain [27].
• In addition to the pleckstrin homology domain and the phosphotyrosine binding domain in insulin receptor substrate (IRS)-1 and IRS-2, a region between amino acids 591 and 786 in IRS-2 (IRS-2-(591-786)) binds to the insulin receptor [28].

Regulatory relationships of PLEK

• PKC alpha pseudosubstrate peptide inhibited pleckstrin phosphorylation, the binding of pleckstrin and secretion [29].
• Protein kinase B (PKB)/Akt is a growth-factor-regulated serine/threonine kinase which contains a pleckstrin homology domain [30].
• PTEN removal of the phosphate from PtdIns(3,4,5)P(3) inhibits this pathway by preventing localisation of proteins with pleckstrin homology domains to the cell membrane [31].
• These data indicate that the NH(2)-terminal PH domain of pleckstrin induces reorganization of the actin cytoskeleton via a pathway dependent on Rac but independent of Cdc42 and phosphatidylinositol 3-kinase [32].
• Expression of a chimeric protein composed of the extracellular and transmembrane portion of Tac fused to the cytoplasmic tail of beta3 completely blocked pleckstrin-mediated spreading, whereas chimeras containing the cytoplasmic tail of beta3 Ser753Pro or alphaIIb had no effect [33].

Other interactions of PLEK

• A Gbetagamma binding site of GRK2 is localized in the carboxyl-terminal pleckstrin homology domain [34].
• Heterologous pleckstrin homology domains do not couple IRS-1 to the insulin receptor [35].
• In one scenario, beta gamma-subunits of G proteins (G beta gamma) activate certain GRKs (beta-adrenergic receptor kinases 1 and 2, or GRK2 and GRK3), via a pleckstrin homology domain in the COOH terminus [36].
• The effects of these lipids were prevented by two well known G beta gamma-binding proteins, phosducin and GST-beta ARK-(466-689) fusion protein, suggesting that the G beta gamma-binding domain (possibly the pleckstrin homology domain) of the GRKs is also a site for lipid:protein interaction [36].
• RACK1, a protein kinase C anchoring protein, coordinates the binding of activated protein kinase C and select pleckstrin homology domains in vitro [37].

Analytical, diagnostic and therapeutic context of PLEK

• Using multiple sequence alignments and phylogenetic tree reconstructions, we find that 6 subfamilies of the DEP domain exist, of which pleckstrin represents a novel and distinct subfamily [16].
• Molecular cloning of a novel diacylglycerol kinase isozyme with a pleckstrin homology domain and a C-terminal tail similar to those of the EPH family of protein-tyrosine kinases [38].
• These findings and failure to detect multimers after treatment of the protein with dimethyl suberimidate indicate that P47 normally exists as a monomer [39].
• Immunofluorescence analysis showed that PLC(eta)2 was localized predominantly to the plasma membrane at resting state via the pleckstrin homology domain [40].
• We employed a pleckstrin homology domain-containing fluorescent biosensor, phospholipase C partial differential pleckstrin homology domain-enhanced green fluorescent protein, to visualize Ins(1,4,5)P3 dynamics in insulin-secreting MIN6 cells and mouse islets in real time using a video-rate confocal system [41].

References