Activation of TRPC Cationic Channels by Mercurial Compounds Confers the Cytotoxicity of Mercury Exposure

Abstract

Mercury is an established worldwide environmental pollutant with well-known toxicity affecting neurodevelopment in humans, but the molecular basis of cytotoxicity and the detoxification procedure are still unclear. Here we examined the involvement of the canonical transient receptor potential (TRPC) channel in the mercury-induced cytotoxicity and the potential detoxification strategy. Whole-cell and excised patches, Ca(2+) imaging, and site-directed mutagenesis were used to determine the mechanism of action of mercurial compounds on TRPC channels overexpressed in HEK293 cells, and cytotoxicity and preventive effect were investigated in cell culture models using small interfering RNA and pharmacological blockers. Mercury potently activates TRPC4 and TRPC5 channels. The extracellular cysteine residues (C(553) and C(558)) near the channel pore region of TRPC5 are the molecular targets for channel activation by mercury. The sensitivity of mercury to TRPC5 is presumed to be specific because other divalent heavy metal pollutants, such as Cd(2+), Ni(2+), and Zn(2+), had no stimulating effect, and TRPC3, TRPC6, TRPV1, and TRPM2 were resistant to mercurial compounds. The channel activity of TRPC5, as well as TRPC4, induced by mercury, was prevented by 2-aminoethoxydiphenyl borate and modified by a reducing environment. The inhibition of TRPC5 channels by specific TRPC5 pore-blocking antibody or by SKF-96365 alleviated the cytotoxicity, whereas the mercury chelator, meso-2,3-dimercaptosuccinic acid, showed nonselective prevention of cell survival. Silencing of the TRPC5 gene reduced the mercury-induced neuronal damage. These results indicate that mercurial compounds are activators for TRPC5 and TRPC4 channels. Blockade of TRPC channels could be a novel strategy for preventing mercury-induced cytotoxicity and neurodevelopment impairment.

Defining potential roles of Pb2+in neurotoxicity from a calciomics approach

“…As these interactions are not dependent on CaM, they represent an allosteric effect where toxic metals are binding opportunistically on the protein surface. These results also suggest that blocking of Trcp5 may present an approach to preventing neurotoxic effects of these metals (35). …”

The effects of para-chloromercuribenzoic acid and different oxidative and sulfhydryl agents on a novel, non-AT1, non-AT2 angiotensin binding site identified as neurolysin

“…Both compounds displayed what appeared to be competitive inhibition of the unmasking effect. Protein cysteine sulfhydryls are a known target of HgCl 2 [74,75]. Silver ion also binds avidly to the SH of protein cysteines, and the ability of AgNO 3 to alter ion currents in frog oocytes is dependent on its ability to bind to free SH groups of cysteines [76].…”

Store-independent pathways for cytosolic STIM1 clustering in the regulation of store-operated Ca2+ influx

“…The molecular basis for SOCs has been linked to the two major ion channel families, i.e., ORAI channels and transient receptor potential (TRP) channels. ORAI channels mediate a highly Ca 2+ -selective and inward rectifying Ca 2+ release-activated Ca 2+ current (I CRAC ) [2,3], while TRPC channels mediate a non-selective Ca 2+ -permeable cationic current with a current-voltage (IV) relationship of outward rectification, such as TRPC1, TRPC3, TRPC7 and the heteromeric TRPC1/TRPC5 channel [4][5][6], or ''N'' shape IV curve with inward and outward rectification [7]. ORAI channels, as well as TRPCs, are interacted or triggered by the endoplasmic reticulum (ER) Ca 2+ sensor STIM1 (stromal interaction molecule 1) that signals the Ca 2+ depletion of ER to the SOCs [8][9][10][11][12].…”