ABSTRACT
The honeybee is a model system to study learning and memory, and Ca(2+) signals play a key role in these processes. We have cloned, expressed, and characterized the first honeybee Ca(2+) channel subunit. We identified two splice variants of the Apis CaVß Ca(2+) channel subunit (Am-CaVß) and demonstrated expression in muscle and neurons. Although AmCaVß shares with vertebrate CaVß subunits the SH3 and GK domains, it beholds a unique N terminus that is alternatively spliced in the first exon to produce a long (a) and short (b) variant. When expressed with the CaV2 channels both, AmCaVßa and AmCaVßb, increase current amplitude, shift the voltage-sensitivity of the channel, and slow channel inactivation as the vertebrate CaVß2a subunit does. However, as opposed to CaVß2a, slow inactivation induced by Am-CaVßa was insensitive to palmitoylation but displayed a unique PI3K sensitivity. Inactivation produced by the b variant was PI3K-insensitive but staurosporine/H89-sensitive. Deletion of the first exon suppressed the sensitivity to PI3K inhibitors, staurosporine, or H89. Recording of Ba(2+) currents in Apis neurons or muscle cells evidenced a sensitivity to PI3K inhibitors and H89, suggesting that both AmCaVß variants may be important to couple cell signaling to Ca(2+) entry in vivo. Functional interactions with phospho-inositide and identification of phosphorylation sites in AmCaVßa and AmCaVßb N termini, respectively, suggest that AmCaVß splicing promoted two novel and alternative modes of regulation of channel activity with specific signaling pathways. This is the first description of a splicing-dependent kinase switch in the regulation of Ca(2+) channel activity by CaVß subunit.
Subject(s)
Action Potentials , Bees/metabolism , Calcium Channels/metabolism , Insect Proteins/metabolism , Alternative Splicing , Amino Acid Sequence , Animals , Bees/chemistry , Bees/genetics , Calcium Channel Blockers/pharmacology , Calcium Channels/chemistry , Calcium Channels/genetics , Cells, Cultured , Exons , Gene Deletion , HEK293 Cells , Humans , Insect Proteins/chemistry , Insect Proteins/genetics , Molecular Sequence Data , Muscle Fibers, Skeletal/physiology , Neurons/physiology , Phosphatidylinositol 3-Kinases/pharmacology , Phosphoinositide-3 Kinase Inhibitors , Phosphorylation , Protein Kinase Inhibitors/pharmacology , Protein Structure, Tertiary , Protein Subunits/chemistry , Protein Subunits/genetics , Protein Subunits/metabolism , XenopusABSTRACT
Innate immunity plays a critical role in the host response to a viral infection. In particular, type I interferons (IFN-I) are major effectors of antiviral innate immunity. Herein, interplays between HTLV-1 and the IFN-I response are reviewed. Particular emphasis is put on virus sensing by innate immunity receptors and on anti-HTLV-1 effects of IFN-I. We also discuss HTLV-1-induced alteration of IFN-I function and how IFN-I/AZT treatment of adult T-cell leukemia/lymphoma patients can lead to complete remission despite virus-induced escape mechanisms.