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

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 Ca influx and gene activation suggests an alternative activation pathway. Here, we demonstrate that membrane depolarization of HEK293 cells transfected with α1.2/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 α1.2/β2b/α2δ, a mutation that disrupts the interaction between α1.2 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 Ca-impermeable mutant channel α1.2/β2b/α2δ or disrupting Ca/calmodulin binding to the channel using the channel mutant α1.2/β2b/α2δ, we demonstrate that depolarization-induced c-Fos and MeCP2 activation does not depend on Ca transport by the channel. Thus, in contrast to the paradigm that elevated intracellular Ca drives nuclear signaling, we show that Cav1.2-triggered c-Fos or MeCP2 is dependent on extracellular Ca and Ca occupancy of the open channel pore, but is Ca-influx independent. An indispensable β-subunit interaction with H-Ras, which is triggered by conformational changes at α1.2 independently of Ca 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.