HIF-1α Dependent Upregulation of ZIP8, ZIP14, and TRPA1 Modify Intracellular Zn Accumulation in Inflammatory Synoviocytes.

Intracellular free zinc ([Zn]) is mobilized in neuronal and non-neuronal cells under physiological and/or pathophysiological conditions; therefore, [Zn] is a component of cellular signal transduction in biological systems. Although several transporters and ion channels that carry Zn have been identified, proteins that are involved in Zn supply into cells and their expression are poorly understood, particularly under inflammatory conditions. Here, we show that the expression of Zn transporters ZIP8 and ZIP14 is increased via the activation of hypoxia-induced factor 1α (HIF-1α) in inflammation, leading to [Zn] accumulation, which intrinsically activates transient receptor potential ankyrin 1 (TRPA1) channel and elevates basal [Zn]. In human fibroblast-like synoviocytes (FLSs), treatment with inflammatory mediators, such as tumor necrosis factor-α (TNF-α) and interleukin-1α (IL-1α), evoked TRPA1-dependent intrinsic Ca oscillations. Assays with fluorescent Zn indicators revealed that the basal [Zn] concentration was significantly higher in TRPA1-expressing HEK cells and inflammatory FLSs. Moreover, TRPA1 activation induced an elevation of [Zn] level in the presence of 1 μM Zn in inflammatory FLSs. Among the 17 out of 24 known Zn transporters, FLSs that were treated with TNF-α and IL-1α exhibited a higher expression of and . Their expression levels were augmented by transfection with an active component of nuclear factor-κB P65 and HIF-1α expression vectors, and they could be abolished by pretreatment with the HIF-1α inhibitor echinomycin (Echi). The functional expression of ZIP8 and ZIP14 in HEK cells significantly increased the basal [Zn] level. Taken together, Zn carrier proteins, TRPA1, ZIP8, and ZIP14, induced under HIF-1α mediated inflammation can synergistically change [Zn] in inflammatory FLSs.