Disease relevance of TRPC4

• These results suggest that platelet CCE channel complexes contain TRPC4 as a molecular component that determines sensitivity of CCE to intracellular alkalosis [1].
• The increases of CCE amplitude and ISOC current density by hypoxia were paralleled by enhanced TRPC4 mRNA and protein expression [2].

High impact information on TRPC4

• 4) Expression of dominant-negative TRPC4 proteins suppressed TRPC3-related channel activity in the HEK293 expression system and in native endothelial cells [3].
• To identify them, we generated chimeras by swapping the different domains of TRPC4 with the same regions in TRPC6 [4].
• However, chimeras containing only the ankyrin repeats or only the coiled-coil domain of TRPC4 did not coimmunoprecipitate with TRPC4 [4].
• Expression of antisense TRPC1 decreased (i) Tg- and OAG-stimulated currents and Ca2+ entry and (ii) the level of endogenous TRPC1 but not TRPC4 [5].
• We report that two tyrosine residues in the C terminus of human TRPC4 (hTRPC4), Tyr-959 and Tyr-972, are phosphorylated following epidermal growth factor (EGF) receptor stimulation of COS-7 cells [6].

Biological context of TRPC4

• By immunocytochemistry, TRPC3 and TRPC4 were localised to cytotrophoblast cells in first trimester placentas and to the syncytiotrophoblast in term placentas [7].
• More importantly, knockout models of TRPC4 have proven that this channel is functionally involved in the regulation of endothelial-dependent vasorelaxation and in the control of EC barrier function [8].
• Impairment of store-operated Ca2+ entry in TRPC4(-/-) mice interferes with increase in lung microvascular permeability [9].
• These data implicate TRPC4 in the regulation of calcium homeostasis in astrocytes, particularly as part of a signaling complex that forms at junctional sites between astrocytes [10].
• Using transfection of astrocytes with myc-tagged TRPC4 or TRL-motif truncated TRPC4 (deltaTRL), we found that deltaTRL localized predominantly to a juxtanuclear compartment, whereas the wild-type protein showed cell surface distribution [10].

Anatomical context of TRPC4

• Immunofluorescence microscopy demonstrated localization of TRPC1, TRPC3, and TRPC4 to the PMN cell membrane and their internalization after cytoskeletal reorganization by calyculin A (CalyA) [11].
• TRPC1, TRPC4 and TRPC5 were associated with detergent-resistant platelet membranes, from which they were partially released when the cells were cholesterol-depleted using methyl-beta-cyclodextrin [12].
• In intact arteries, TRPC4 expression correlated with the amount of endothelium present [13].
• In contrast TRPC4 and TRPC5 mRNAs were predominantly expressed in HK-2 and HEK-293 cell lines respectively [14].
• The defect in Ca2+ influx in TRPC4(-/-) endothelial cells was associated with lack of thrombin-induced actin-stress fiber formation and a reduced endothelial cell retraction response [9].

Associations of TRPC4 with chemical compounds

• Unlike most other TRP-related channels, which are inhibited by La(3+) and Gd(3+), currents through TRPC4 and TRPC5 are potentiated by La(3+) [15].
• TRPC3 and TRPC4 are activated by oxidants, which induce Na(+) and Ca(2+) entry into cells through mechanisms that are dependent on phospholipase C. TRPM2 is activated by oxidative stress or TNFalpha, and the mechanism involves production of ADP-ribose, which binds to an ADP-ribose binding cleft in the TRPM2 C-terminus [16].
• Over-expression of TRPC4 in HEK293 cells was found to result in a gain of pH-sensitivity of CCE with clearly detectable promotion of CCE in response to monensin [1].
• Alternative splice variants of hTrp4 differentially interact with the C-terminal portion of the inositol 1,4,5-trisphosphate receptors [17].
• A similar distribution was observed in fundal myometrium samples from patients before and after the onset of labor. hTrpC4 mRNA was significantly lower after the onset of labor; there were no significant changes in the concentrations of other TrpC mRNAs [18].

Physical interactions of TRPC4

• Using GST fusion proteins, we found that TRPC4 interacted with the PDZ1 domain of ZO-1 and that this was also dependent on the TRL motif [10].
• Protein 4.1 interacts with TRPC4 and the membrane skeleton [19].

Co-localisations of TRPC4

• Canonical transient receptor potential channel 4 (TRPC4) co-localizes with the scaffolding protein ZO-1 in human fetal astrocytes in culture [10].

Regulatory relationships of TRPC4

• In addition, EGF receptor stimulation induced the exocytotic insertion of hTRPC4 into the plasma membrane dependent on the activity of STKs and was accompanied by a phosphorylation-dependent increase in the association of hTRPC4 with Na(+)/H(+) exchanger regulatory factor [6].
• The increase in lung microvascular permeability in response to PAR-1 activation was inhibited in TRPC4-/- mice [20].

Other interactions of TRPC4

• Knockdown of the level of endogenous TRPC1 or TRPC4 inhibited store-operated calcium entry, indicating they are part of the native SOC [21].
• In all of these cells, hTrpC1 and hTrpC4 mRNAs were the most abundant, followed by hTrpC6 [18].
• The functional effects of EBP50 on TRPC4/5 activity have not been investigated [22].
• There is good evidence that it can heteromultimerise with the related proteins TRPC4, TRPC5 and polycystin-2; a tetrameric arrangement is envisaged, but not demonstrated [23].
• In addition, TRPC4-/- mouse-lung endothelial cells exhibited lack of actin-stress fiber formation and cell retraction in response to thrombin activation of protease-activated receptor-1 (PAR-1) in endothelial cells [20].

Analytical, diagnostic and therapeutic context of TRPC4

• Immunoprecipitation of TRPC1 pulled down TRPC3 but not TRPC4 [5].
• In isolated-perfused mouse lungs, the PAR-1 agonist peptide increased microvessel filtration coefficient (K(f,c)), a measure of vascular permeability, by a factor of 2.8 in wt and 1.4 in TRPC4(-/-); La3+ (1 micromol/L) addition to wt lung perfusate reduced the agonist effect to that observed in TRPC4(-/-) [9].
• Using a yeast two-hybrid assay and glutathione-S-transferase-pulldown experiments, we found that the C-terminus of alpha-hTrp4, but not of beta-hTrp4, associates in vitro with the C-terminal domain of the InsP(3) receptors type 1, 2 and 3 [17].
• Members of the transient receptor potential (TRP) family of nonselective cation channels, TRPC1, TRPC4, and TRPC6, were detected by reverse transcription-polymerase chain reaction and Western blot in both A7r5 cells and MASMC [24].
• Using a RT-PCR technique, a novel isoform of TRPC4, designated rTRPC4gamma, was isolated [25].

References