Author:
Abdullah Huda Ismail,Pedraza Paulina L.,McGiff John C.,Ferreri Nicholas R.
Abstract
We evaluated the contribution of calcium-sensing receptor (CaR)-mediated Gi-coupled signaling to TNF production in medullary thick ascending limb (mTAL) cells. A selective Gi inhibitor, pertussis toxin (PTX), but not the inactive B-oligomer binding subunit, abolished CaR-mediated increases in TNF production. The inhibitory effect of PTX was partially reversed by using an adenylate cyclase inhibitor. CaR-mediated TNF production also was partially reversed by a cAMP analog, 8-Br-cAMP. IP1 accumulation was CaR dependent and blocked by PI-PLC; partial inhibition also was observed with PTX. CaR increased calcineurin (CaN) activity by approximately threefold, and PTX prevented CaR-mediated increases in CaN activity, an nuclear factor of activated T cells (NFAT)- cis reporter construct, and a TNF promoter construct. The interaction between Gi and PKC was determined, as we previously showed that CaR-mediated TNF production was CaN and NFAT- mediated and Gq dependent. CaR activation increased PKC activity by twofold, an effect abolished by transient transfection with a dominant negative CaR construct, R796W, or pretreatment with PTX. Inhibition with the pan-specific PKC inhibitor GF 109203X (20 nM) abolished CaR-mediated increases in activity of CaN, an NFAT reporter, and a TNF promoter construct. Collectively, the data suggest that Gi-coupled signaling contributes to NFAT-mediated TNF production in a CaN- and PKC-dependent manner and may be part of a CaR mechanism to regulate mTAL function. Moreover, concurrent Gq and Gi signaling is required for CaR-mediated TNF production in mTAL cells via a CaN/NFAT pathway that is PKC dependent. Understanding CaR-mediated signaling pathways that regulate TNF production in the mTAL is crucial to defining novel mechanisms that regulate extracellular fluid volume and salt balance.
Publisher
American Physiological Society
Cited by
20 articles.
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