Cacnb4 directly couples electrical activity to gene expression, a process defective in juvenile epilepsy.

Calcium current through voltage-gated calcium channels (VGCC) controls gene expression. Here, we describe a novel signalling pathway in which the VGCC Cacnb4 subunit directly couples neuronal excitability to transcription. Electrical activity induces Cacnb4 association to Ppp2r5d, a regulatory subunit of PP2A phosphatase, followed by (i) nuclear translocation of Cacnb4/Ppp2r5d/PP2A, (ii) association with the tyrosine hydroxylase (TH) gene promoter through the nuclear transcription factor thyroid hormone receptor alpha (TRα), and (iii) histone binding through association of Cacnb4 with HP1γ concomitantly with Ser(10) histone H3 dephosphorylation by PP2A. This signalling cascade leads to TH gene repression by Cacnb4 and is controlled by the state of interaction between the SH3 and guanylate kinase (GK) modules of Cacnb4. The human R482X CACNB4 mutation, responsible for a form of juvenile myoclonic epilepsy, prevents association with Ppp2r5 and nuclear targeting of the complex by altering Cacnb4 conformation. These findings demonstrate that an intact VGCC subunit acts as a repressor recruiting platform to control neuronal gene expression.

A Ca(v)3.2/syntaxin-1A signaling complex controls T-type channel activity and low-threshold exocytosis.

T-type calcium channels represent a key pathway for Ca(2+) entry near the resting membrane potential. Increasing evidence supports a unique role of these channels in fast and low-threshold exocytosis in an action potential-independent manner, but the underlying molecular mechanisms have remained unknown. Here, we report the existence of a syntaxin-1A/Ca(v)3.2 T-type calcium channel signaling complex that relies on molecular determinants that are distinct from the synaptic protein interaction site (synprint) found in synaptic high voltage-activated calcium channels. This interaction potently modulated Ca(v)3.2 channel activity, by reducing channel availability. Other members of the T-type calcium channel family were also regulated by syntaxin-1A, but to a smaller extent. Overexpression of Ca(v)3.2 channels in MPC 9/3L-AH chromaffin cells induced low-threshold secretion that could be prevented by uncoupling the channels from syntaxin-1A. Altogether, our findings provide compelling evidence for the existence of a syntaxin-1A/T-type Ca(2+) channel signaling complex and provide new insights into the molecular mechanism by which these channels control low-threshold exocytosis.

The spatial organization of proton and lactate transport in a rat brain tumor.

Tumors create a heterogeneous acidic microenvironment which assists their growth and which must be taken into account in the design of drugs and their delivery. In addition, the acidic extracellular pH (pHe) is itself exploited in several experimental techniques for drug delivery. The way the acidity is created is not clear. We report here the spatial organization of key proton-handling proteins in C6 gliomas in rat brain. The mean profiles across the tumor rim of the Na+/H+ exchanger NHE1, and the lactate-H+ cotransporter MCT1, both showed peaks. NHE1, which is important for extension and migration of cells in vitro, showed a peak 1.55 times higher than in extratumoural tissue at 0.33 mm from the edge. MCT1 had a broader peak, further into the tumor (maximum 1.76 fold at 1.0 mm from the edge). In contrast, MCT4 and the carbonic anhydrase CAIX, which are associated with hypoxia, were not significantly upregulated in the rim. The spatial distribution of MCT4 was highly correlated with that of CAIX, suggesting that their expression is regulated by the same factors. Since protons extruded by NHE1 diffuse away through extracellular clefts, NHE1 requires a continuous source of intracellular protons. From the stoichiometries of metabolic pathways that produce or consume H+, and the greater availability of glucose compared to oxygen in most parts of a tumor, we support the classic view that most of the net proton efflux from C6 gliomas originates in glycolytic formation of lactate and H+ inside the tumor, but add that some lactate is taken up into cells in the rim on MCT1, and some lactate diffuses away, leaving its associated protons available to re-enter cells for extrusion on NHE1. Therapeutic inhibition of NHE1, MCT1 or CAIX is predicted to affect different parts of a tumor.

Gene regulation by voltage-dependent calcium channels.

Ca2+ is the most widely used second messenger in cell biology and fulfills a plethora of essential cell functions. One of the most exciting findings of the last decades was the involvement of Ca2+ in the regulation of long-term cell adaptation through its ability to control gene expression. This finding provided a link between cell excitation and gene expression. In this review, we chose to focus on the role of voltage-dependent calcium channels in mediating gene expression in response to membrane depolarization. We illustrate the different pathways by which these channels are involved in excitation-transcription coupling, including the most recent Ca2+ ion-independent strategies that highlight the transcription factor role of calcium channels.