β-Subunit of the voltage-gated Ca²⁺ channel Cav1.2 drives signaling to the nucleus via H-Ras

Abstract

Depolarization-induced signaling to the nucleus by the L-type voltage-gated calcium channel Cav1.2 is widely assumed to proceed by elevating intracellular calcium. The apparent lack of quantitative correlation between Ca²⁺ influx and gene activation suggests an alternative activation pathway. Here, we demonstrate that membrane depolarization of HEK293 cells transfected with α₁1.2/β2b/α2δ subunits (Cav1.2) triggers c-Fos and MeCP2 activation via the Ras/ERK/CREB pathway. Nuclear signaling is lost either by absence of the intracellular β2 subunit or by transfecting the cells with the channel mutant α₁1.2^W440A/β2b/α2δ, a mutation that disrupts the interaction between α₁1.2 and β2 subunits. Pulldown assays in neuronal SH-SY5Y cells and in vitro binding of recombinant H-Ras and β2 confirmed the importance of the intracellular β2 subunit for depolarization-induced gene activation. Using a Ca²⁺-impermeable mutant channel α₁1.2^L745P/β2b/α2δ or disrupting Ca²⁺/calmodulin binding to the channel using the channel mutant α₁1.2^I1624A/β2b/α2δ, we demonstrate that depolarization-induced c-Fos and MeCP2 activation does not depend on Ca²⁺ transport by the channel. Thus, in contrast to the paradigm that elevated intracellular Ca²⁺ drives nuclear signaling, we show that Cav1.2-triggered c-Fos or MeCP2 is dependent on extracellular Ca²⁺ and Ca²⁺ occupancy of the open channel pore, but is Ca²⁺-influx independent. An indispensable β-subunit interaction with H-Ras, which is triggered by conformational changes at α₁1.2 independently of Ca²⁺ flux, brings to light a master regulatory role of β2 in transcriptional activation via the ERK/CREB pathway. This mode of H-Ras activation could have broad implications for understanding the coupling of membrane depolarization to the rapid induction of gene transcription.