Aktuelle Neurologie 2009; 36 - V244
DOI: 10.1055/s-0029-1238434

Induction of T-type calcium channel Cav3.2 expression by zinc via MTF-1 promoter activation

C Schaub 1, K Pernhorst 1, H Beck 1, S Schoch 1, Y Yaari 1, AJ Becker 1
  • 1Bonn; Jerusalem, IL

Rationale: Brain neurons contain substantial amounts of Zn2+, which plays multiple roles in cellular functions. Whereas the release of Zn2+ into the interstitium reportedly modulate various neurotransmitter receptors and ion channels, only little is known about the effects of intracellular Zn2+ (Zn2+_in) on transcription of genes critical for neuronal excitability.

Methods: Here, we address whether Zn2+_in controls the transcription of Ni2+-sensitive Ca2+ channels, i.e. R/T-type Ca2+ currents mediated by the α1 subunits Cav2.3 and Cav3.1–3.3. In NG108–15 neuroblastoma cells, transient exposure to 200 uM Zn2+ under depolarizing conditions (50 mM KCl) led to Zn2+ influx via L-type (BayK-sensitive) Ca2+ channels, and to increased mRNA transcription of Cav3.2, but not of other R/T-type Ca2+ channels.

Results: Promoter analysis of Cav3.2 revealed a 1.164bp fragment within the 5' UTR-flanking genomic sequence harboring several metal regulatory elements (MRE) for the metal-responsive transcription factor-1 (MTF-1). In a Luciferase assay, exposure to Zn2+ strongly induced transcription of this 1.164bp Cav3.2 promoter fragment. Similar effects were induced by the NO-donor Na+ nitroprusside, which causes liberation of intracellular Zn2+ bound to endogenous chelators. In an electrophoretic mobility shift assay in NG108–15 cells, Zn2+ exposure resulted in increased binding of MTF-1 to MREs. Overexpression of MTF-1 was sufficient to augment Cav3.2 promoter activation levels, as after exposure to Zn2+. Functional inhibition of MTF-1 by overexpression of a dominant negative MTF-1 construct reversed the effects of Zn2+ on Cav3.2 promoter activation.

Conclusions: Our findings implicate Cav3.2 as a novel target for MTF-1-mediated transcriptional upregulation via transient increases in intracellular free Zn2+. Since brain injuries are accompanied by marked elevations in intracellular free Zn2+, and since Cav3.2 upregulation profoundly enhances neuronal discharge, we propose that the novel upregulation of Cav3.2 transcription by zinc may be a key process in injury-induced epileptogenesis.