CALCIUM CHANNELS, CALMODULIN AND NUCLEAR CREB SIGNALING

Stanford University, Stanford CA

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Abstract

DESCRIPTION (provided by applicant):This grant proposal addresses fundamental questions in cellular signal transduction: how are cells able to use Ca2+ signals for so many different functions, some in apparent opposition to each other? Given that Ca2+ enters the cell via many routes, what enables some sources and not others to activate nuclear transcription? How can local changes in Ca2+ near the mouths of Ca2+ channels trigger profound changes in the nucleus, tens or hundreds of micrometers away? The experiments will link L-type Ca channels and calmodulin to nuclear CREB signaling. Recent advances from our lab and from others have revealed that Ca2+/CaM engages in an intricate interplay with the pore-forming a1C subunit of L-type Ca2+ channels. Binding of Ca2+/CaM to an "IQ-motif" in the C-terminal tail of a1C mediates Ca2+-dependent regulation of channel gating and also initiates excitation-transcription coupling. To gain further insights, the following specific aims are proposed: (1) to dissect automodulation of L-type channel gating as a readily accessible model system for understanding how L-type Ca channel-CaM interactions trigger downstream signaling. The importance of tethering apocalmodulin will be assessed as a prerequisite for various local signaling mechanisms. Channel components that act downstream of the formation of the CaM-IQ complex will be identified. A novel working hypothesis for the mechanism of Ca2+-dependent inactivation will be tested. (2) Local and long-distance signaling mechanisms that link Ca2+ entry through L-type channels to nuclear transcription will be delineated. Two signaling pathways will be considered, one mediated by NF-AT movement to the nucleus, the other supported by CaM translocation to the nucleus and activation of a cascade of CaM kinases. The molecular basis of the privileged role of L-type channels in excitation-transcription coupling will be explored. (3) Armed with knowledge about molecular events underlying excitation-transcription coupling, we will study how this communication operates in a physiological context. We will test whether a1D subunits help support selective responses to excitatory postsynaptic potentials. The role of CaM translocation in supporting "paired-pulse facilitation" will be explored by applying weak stimuli separated in time or spatial location. We will look for CREB phosphorylation in circuits critical for learning and memory and survey the array of genes activated by Ca2 entry through L-type channel using cDNA microarrays.