Molecular Basis for Zinc Transporter 1 Action as an Endogenous Inhibitor of L-type Calcium Channels

Abstract

The L-type calcium channel (LTCC) has a variety of physiological roles that are critical for the proper function of many cell types and organs. Recently, a member of the zinc-regulating family of proteins, ZnT-1, was recognized as an endogenous inhibitor of the LTCC, but its mechanism of action has not been elucidated. In the present study, using two-electrode voltage clamp recordings in Xenopus oocytes, we demonstrate that ZnT-1-mediated inhibition of the LTCC critically depends on the presence of the LTCC regulatory ␤-subunit. Moreover, the ZnT-1-induced inhibition of the LTCC current is also abolished by excess levels of the ␤-subunit. An interaction between ZnT-1 and the ␤-subunit, as demonstrated by co-immunoprecipitation and by fluorescence resonance energy transfer, is consistent with this result. Using surface biotinylation and total internal reflection fluorescence microscopy in HEK293 cells, we show a ZnT-1-dependent decrease in the surface expression of the pore-forming ␣ 1 -subunit of the LTCC. Similarly, a decrease in the surface expression of the ␣ 1 -subunit is observed following up-regulation of the expression of endogenous ZnT-1 in rapidly paced cultured cardiomyocytes. We conclude that ZnT-1-mediated inhibition of the LTCC is mediated through a functional interaction of ZnT-1 with the LTCC ␤-subunit and that it involves a decrease in the trafficking of the LTCC ␣ 1 -subunit to the surface membrane.

Tissue Nonspecific Alkaline Phosphatase Is Activated via a Two-step Mechanism by Zinc Transport Complexes in the Early Secretory Pathway

“…For example, the Xenopus copper transporter CTR1 is thought to be a critical component of the membrane-associated FGF signaling complex, transducing FGF signals independently of copper (38). ZnT1 has been shown to regulate Raf1 biological activity, down-regulate transcription factors stimulated by MTF1, c-Jun, and Elk, or inhibit L-type calcium channels by decreasing the trafficking of the L-type calcium channel ␣ 1 -subunit (28,39,40). Our findings here are novel in that ZnTs are involved in the regulation of protein stability in addition to supplying zinc.…”

Recent advances in the molecular pathophysiology of atrial fibrillation

“…Loss of receptor-mediated I K,ACh channel control is associated with increased agonist-independent ("constitutive") I K,AChc (69,71,79,85). Increased I K,AChc is due to enhanced single I K,ACh channel opening frequency, without changes in single-channel conductance, density, or voltage dependence (85).…”

The Physiological, Biochemical, and Molecular Roles of Zinc Transporters in Zinc Homeostasis and Metabolism

“…ZnT1, which forms a hetero-complex with EVER proteins, downregulates the transcription factors stimulated by MTF-1, c-Jun, and Elk. ZnT1 also interacts with the regulatory ␤-subunit of the L-type calcium channel (LTCC), which reduces the capacity of the ␤-subunit to chaperone the pore-forming ␣ 1 -subunit of LTCC to the cell surface (236). ZnT1 enhances the activity and surface expression of the T-type calcium channel, which is regulated via activation of Ras-ERK signaling (287).…”