Disease relevance of Plec1

• Caspase 8-mediated cleavage of plectin precedes F-actin breakdown in acinar cells during pancreatitis [1].
• Moreover, hereditary gene defects in plectin cause epidermolysis bullosa simplex (EBS)-MD, a severe skin blistering disease with muscular dystrophy [2].
• These high Mr polypeptide species and a few bands of slightly lower Mr (most likely proteolytic breakdown products) were shown to react with antibodies to rat glioma C6 cell plectin using immunoautoradiography and/or immunoprecipitation [3].
• In contrast, induction of CAT activity in cultures containing MMTVCAT, a plasmid containing the CAT gene controlled by the mouse mammary tumor virus long terminal repeat, was unaffected by PCN treatment, required lower concentrations of DEX for a maximal response, and was inhibited by treatment with DEX plus PCN [4].
• After a long period of culture and during aminonucleoside nephrosis, situations when VECs lose differentiated phenotypes, most of the cells had no perinuclear plectin [5].

High impact information on Plec1

• Pretreatment of animals with phenobarbital (PB) or pregnenolone-16 alpha-carbonitrile (PCN) did not influence either microsomal or cytosolic enzyme activities in hamsters, whereas about a tenfold increase in enzyme activities was seen after pretreatment with PB in both rat strains and following PCN in Wistar rats [6].
• Plectin sidearms mediate interaction of intermediate filaments with microtubules and other components of the cytoskeleton [7].
• Our results provide direct structural evidence for the hypothesis that plectin cross-links elements of the cytoskeleton thus leading to integration of the cytoplasm [7].
• Plectin binding to microtubules was significantly increased in cells from transgenic mice lacking IFs and was reversed by microinjection of exogenous vimentin [7].
• The association of IFs with stress fibers survived actin depletion by gelsolin suggesting that myosin II minifilaments or components closely associated with them may play a role as plectin targets [7].

Chemical compound and disease context of Plec1

• Pretreatment with protein-free diet (PFD) or pregnenolone-16 alpha-carbonitrile (PCN) markedly reduces th toxicity of dimethylnitrosamine (DMN) in rats [8].
• A single dose of troleandomycin completely reversed the ability of PCN to protect rats from digitoxin toxicity, establishing the importance of cytochrome P-450p induction in the protective effect of PCN [9].
• This suggests that the induction of cytochrome P-450p and UDP-GT-dt1 does not fully account for the mechanism by which PCN protects rats from digitoxin toxicity [9].
• These data correlate well with previous investigations in which PCN was found to have a beneficial influence on experimentally induced hyperbilirubinemias and, furthermore, there is an indication that phenobarbital, another potent microsomal enzyme inducer, acts via a similar mechanism [10].
• Origins of hepatomegaly produced by dexamethasone (DEX), pregnenolone 16 alpha-carbonitrile (PCN) and phenobarbitone (PB) in female Sprague-Dawley rats [11].

Biological context of Plec1

• Northern blot analysis indicated that there is a significant degree of conservation of plectin genes between rat, human, and chicken and that, as shown previously at the protein level, plectin has a wide tissue distribution [12].
• Naringin-sensitive phosphorylation of plectin, a cytoskeletal cross-linking protein, in isolated rat hepatocytes [13].
• Plectin transcript diversity: identification and tissue distribution of variants with distinct first coding exons and rodless isoforms [2].
• Together, these results suggested that the molecular binding sites of plectin for vimentin and lamin B, as well as the phosphorylation sites for kinase C, were confined to a defined central section of plectin's rod domain [14].
• Southern blot analysis of rat DNA using pP450PCN revealed that approximately 50 to 60 kilobases of DNA reacted with the PCN probe, suggesting the P-450PCN gene is either a very large gene or other genomic segments exist that react with the probe, such as pseudogenes or related P-450 genes that share homology [15].

Anatomical context of Plec1

• Plectin is a versatile cytolinker protein regulating F-actin dynamics in fibroblasts [1].
• These results suggest the existence of a pool of plectin which preferentially associates with IFs but may also be competed for by microtubules [7].
• In smooth muscle cells, regularly spaced lateral densities probably representing myofilament attachment sites were immunoreactive with plectin antibodies [3].
• By indirect immunofluorescence microscopy using frozen sections (4 micron) of stomach, kidney, small intestine, liver, uterus, urinary bladder, and heart, antigens reacting with antibodies to plectin were found in fibroblast, endothelial, smooth, skeletal, and cardiac muscle, nerve, and epithelial cells of various types [3].
• In cross sections through smooth muscle, most strikingly of urinary bladder, antibodies to plectin specifically decorated regularly spaced, spot-like structures at the cell periphery [3].

Associations of Plec1 with chemical compounds

• Inhibitors of protein kinase C, cAMP-dependent protein kinase, or Ca(2+)/calmodulin-dependent kinase II had moderate or no protective effects on plectin network disruption, whereas naringin offered 86% protection [13].
• Use of dilute (5%) polyacrylamide gels containing 6 m urea allowed the resolution of one very large (approximately 500-kDa) okadaic acid- and naringin-sensitive phosphoprotein, identified by tryptic fingerprinting, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and immunostaining as the cytolinker protein, plectin [13].
• These results were corroborated by in vitro recombination studies using vimentin and plectin purified from C6 cells [16].
• P450PCN1 mRNA was induced by PCN, dexamethasone, and phenobarbital in both male and female rats [17].
• In the companion report we used primary cultures of adult rat hepatocytes to demonstrate that glucocorticoids comprise a "class" of compounds that stimulate de novo synthesis of a form of cytochrome P-450 (P450PCN) indistinguishable from that induced by the nonhormonal steroid pregnenolone 16 alpha-carbonitrile (PCN) [18].

Physical interactions of Plec1

• Solid-phase binding to proteolytically degraded vimentin fragments suggested that plectin interacts with the helical rod domain of vimentin, a highly conserved structural element of all intermediate filament proteins [16].

Co-localisations of Plec1

• Immunofluorescence analysis revealed that plectin was colocalized with desmin at the periphery of Z-discs [19].
• Unlike in IF-containing cells, where plectin colocalized largely with the vimentin network, in the IF-negative subclone the protein was mainly associated with polymeric actin structures [20].

Regulatory relationships of Plec1

• Here we show that plectin is expressed in a vimentin-negative C6 cell subclone (C6-D10) at levels similar to those of the vimentin-positive control subclone C6-D8 [20].

Other interactions of Plec1

• Inhibition of caspase 8 before CCK hyperstimulation prevents plectin cleavage, stabilizes F-actin morphology, and reverses the inhibition of secretion [1].
• These results suggest that plectin is a cross-linker of vimentin filaments and possibly also of other intermediate filament types [16].
• Solid-phase binding assays carried out in the presence of Fab fragments of mAbs demonstrated an interference of certain group 1 mAbs in the interactions of plectin with vimentin and lamin B. On the other hand, plectin's self-interaction was inhibited mainly by Fab fragments with epitopes in the peripheral rod domain (group 2 mAbs) [14].
• Immunogold labeling in skinned muscle fibers clearly demonstrated that plectin-labeled fine threads linked desmin intermediate filaments to Z-discs and connected intermediate filaments to each other [19].
• Sequence analysis showed that plectin contains a highly conserved actin-binding domain, consisting of a pair of calponin-like subdomains [21].

Analytical, diagnostic and therapeutic context of Plec1

• Using recombinant proteins we also show by negative staining and rotary shadowing electron microscopy that in vitro assembled vimentin intermediate filaments become packed into dense aggregates upon incubation with plectin repeat 5 domain, in contrast to repeat 4 domain or a mutated repeat 5 domain [22].
• Quantitative evaluation of transcriptional rates in isolated nuclei and intranuclear and cytoplasmic mRNA levels demonstrates that the catatoxic steroids pregnenolone-16 alpha-carbonitrile (PCN) and dexamethasone modulate microsomal drug metabolizing enzymes both positively and negatively at the transcriptional level [23].
• To better understand the functional role of plectin in skeletal muscle fibers, we have examined the topological and structural relationships of plectin to intermediate filaments and Z-discs in rat diaphragm muscles by confocal and immunoelectron microscopy [19].
• Using yeast two-hybrid assays in combination with in vitro binding experiments, we demonstrate that the actin-binding domain of plectin is fully functional and preferentially binds to polymeric actin [21].
• Hydrodynamic properties of plectin in solution were obtained by sedimentation velocity centrifugation and high-pressure liquid chromatography analysis yielding a sedimentation coefficient of 10 S and a Stokes radius of 27 nm [24].

References