Ca2+ influx and protein scaffolding via TRPC3 sustain PKCbeta and ERK activation in B cells

Activation of transient receptor potential canonical 3 (TRPC3)-mediated Ca2+ entry by A1 adenosine receptor in cardiomyocytes disturbs atrioventricular conduction

Although the activation of the A(1)-subtype of the adenosine receptors (A(1)AR) is arrhythmogenic in the developing heart, little is known about the underlying downstream mechanisms. The aim of this study was to determine to what extent the transient receptor potential canonical (TRPC) channel 3, functioning as receptor-operated channel (ROC), contributes to the A(1)AR-induced conduction disturbances. Using embryonic atrial and ventricular myocytes obtained from 4-day-old chick embryos, we found that the specific activation of A(1)AR by CCPA induced sarcolemmal Ca(2+) entry. However, A(1)AR stimulation did not induce Ca(2+) release from the sarcoplasmic reticulum. Specific blockade of TRPC3 activity by Pyr3, by a dominant negative of TRPC3 construct, or inhibition of phospholipase Cs and PKCs strongly inhibited the A(1)AR-enhanced Ca(2+) entry. Ca(2+) entry through TRPC3 was activated by the 1,2-diacylglycerol (DAG) analog OAG via PKC-independent and -dependent mechanisms in atrial and ventricular myocytes, respectively. In parallel, inhibition of the atypical PKCζ by myristoylated PKCζ pseudosubstrate inhibitor significantly decreased the A(1)AR-enhanced Ca(2+) entry in both types of myocytes. Additionally, electrocardiography showed that inhibition of TRPC3 channel suppressed transient A(1)AR-induced conduction disturbances in the embryonic heart. Our data showing that A(1)AR activation subtly mediates a proarrhythmic Ca(2+) entry through TRPC3-encoded ROC by stimulating the phospholipase C/DAG/PKC cascade provide evidence for a novel pathway whereby Ca(2+) entry and cardiac function are altered. Thus, the A(1)AR-TRPC3 axis may represent a potential therapeutic target.

Effect of oxidative stress on TRPM2 and TRPC3 channels in B lymphoblast cells in bipolar disorder

OBJECTIVES

Recent findings implicate the calcium-permeable nonselective ion channels transient receptor potential (TRP) melastatin subtype 2 (TRPM2) and canonical subtype 3 (TRPC3) in the pathogenesis of bipolar disorder (BD). These channels are involved in calcium and oxidative stress signaling, both of which are disrupted in BD. Thus, we sought to determine if these channels are differentially affected by oxidative stress in cell lines of BD patient origin.

METHODS

B lymphoblast cell lines (BLCLs) from bipolar I disorder (BD-I) patients (n = 6) and healthy controls (n = 5) were challenged with the oxidative stressor rotenone (2.5 μM and 10 μM) or vehicle for acute (24 hours) and chronic (four days) intervals. Cell viability was measured using propidium iodide, while TRPM2- and TRPC3-mediated calcium fluxes were measured in the presence of their respective activators (H(2) O(2) and 1-oleoyl-2-acetyl-sn-glycerol) using Fluo-4. Changes in TRPM2 and TRPC3 expression levels were determined by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and Western blotting.

RESULTS

Cell viability decreased with increasing dose and duration of rotenone treatment, with BD-I patient BLCLs more susceptible than controls acutely (p < 0.001). A dose-dependent decrease in TRPC3 protein expression occurred after chronic (24%, p = 0.008) but not acute rotenone treatment. Interestingly, H(2) O(2) -provoked TRPM2-dependent calcium fluxes revealed an interaction between the effects of stressor addition and diagnostic subject group (p = 0.003).

CONCLUSIONS

These data support an important role for TRPM2 and TRPC3 in sensing and responding to oxidative stress and in transducing oxidative stress signaling to intracellular calcium homeostasis and cellular stress responses, all of which have been implicated in the pathophysiology of BD.

The transient receptor potential (TRP) channel TRPC3 TRP domain and AMP-activated protein kinase binding site are required for TRPC3 activation by erythropoietin

Modulation of intracellular calcium ([Ca(2+)](i)) by erythropoietin (Epo) is an important signaling pathway controlling erythroid proliferation and differentiation. Transient receptor potential (TRP) channels TRPC3 and homologous TRPC6 are expressed on normal human erythroid precursors, but Epo stimulates an increase in [Ca(2+)](i) through TRPC3 but not TRPC6. Here, the role of specific domains in the different responsiveness of TRPC3 and TRPC6 to erythropoietin was explored. TRPC3 and TRPC6 TRP domains differ in seven amino acids. Substitution of five amino acids (DDKPS) in the TRPC3 TRP domain with those of TRPC6 (EERVN) abolished the Epo-stimulated increase in [Ca(2+)](i). Substitution of EERVN in TRPC6 TRP domain with DDKPS in TRPC3 did not confer Epo responsiveness. However, substitution of TRPC6 TRP with DDKPS from TRPC3 TRP, as well as swapping the TRPC6 distal C terminus (C2) with that of TRPC3, resulted in a chimeric TRPC6 channel with Epo responsiveness similar to TRPC3. Substitution of TRPC6 with TRPC3 TRP and the putative TRPC3 C-terminal AMP-activated protein kinase (AMPK) binding site straddling TRPC3 C1/C2 also resulted in TRPC6 activation. In contrast, substitution of the TRPC3 C-terminal leucine zipper motif or TRPC3 phosphorylation sites Ser-681, Ser-708, or Ser-764 with TRPC6 sequence did not affect TRPC3 Epo responsiveness. TRPC3, but not TRPC6, and TRPC6 chimeras expressing TRPC3 C2 showed significantly increased plasma membrane insertion following Epo stimulation and substantial cytoskeletal association. The TRPC3 TRP domain, distal C terminus (C2), and AMPK binding site are critical elements that confer Epo responsiveness. In particular, the TRPC3 C2 and AMPK site are essential for association of TRPC3 with the cytoskeleton and increased channel translocation to the cell surface in response to Epo stimulation.

Fibronectin fragment activation of ERK increasing integrin α₅ and β₁ subunit expression to degenerate nucleus pulposus cells

Fibronectin fragments (Fn-f), which are the breakdown products of fibronectin, accumulate in the disc during degeneration and are proved to induce the degeneration of intervertebral disc. The goal of this investigation was to determine the functional role of integrin α₅ β₁, extracellular signal-regulated kinase (ERK), and protein kinase C (PKC) in the process of Fn-f degeneration nucleus pulposus (NP) cells. We found that Fn-f (100 nM, 30 kDa) exposure led to degeneration of NP cells, up-regulation of integrin α₅ β₁ expression and phosphorylation of the ERK(½) . After the expression of integrin α₅ β₁ was silenced in NP cells, the phosphorylation of ERK(½) and the expression of MMP9, MMP13, and collagen II had no difference with control under the treatment of Fn-f. Finally, when the inhibitor of ERK(½) and the inhibitor of PKC were added into the medium of NP cells; we found these two inhibitors could eliminate the effect of Fn-f on NP cells. It is concluded that Fn-f had the potential to enhance the NP cell degeneration in a vicious circle. And the integrin α₅ β₁ subunit, ERK, and PKC were all included in this loop.