The voltage-gated potassium channel Kv1.2 undergoes tyrosine phosphorylation-dependent suppression of its ionic current. However, little is known about the physical mechanism behind that process. We have found that the Kv1.2 alpha-subunit protein undergoes endocytosis in response to the same stimuli that evoke suppression of Kv1.2 ionic current. The process is tyrosine phosphorylation-dependent because the same tyrosine to phenylalanine mutation in the N-terminus of Kv1.2 that confers resistance to channel suppression (Y132F) also confers resistance to channel endocytosis. Overexpression of a dominant negative form of dynamin blocked stimulus-induced Kv1.2 endocytosis and also blocked suppression of Kv1.2 ionic current. These data indicate that endocytosis of Kv1.2 from the cell surface is a key mechanism for channel suppression by tyrosine kinases.

Tyrosine phosphorylation evokes functional changes in a variety of ion channels. Modulation of the actin cytoskeleton also affects the function of some channels. Little is known about how these avenues of ion channel regulation may interact. We report that the potassium channel Kv1.2 associates with the actin-binding protein cortactin and that the binding is modulated by tyrosine phosphorylation. Immunocytochemical and biochemical analyses show that Kv1.2 and cortactin co-localize to the cortical actin cytoskeleton at the leading edges of the cell. Binding assays using purified recombinant proteins reveal a 19-amino acid span within the carboxyl terminus of Kv1.2 that is necessary for direct cortactin binding. Phosphorylation of specific tyrosines within the C terminus of Kv1.2 attenuates that binding. In HEK293 cells, activation of the M1 muscarinic acetylcholine receptor evokes tyrosine phosphorylationdependent suppression of Kv1.2 ionic current. We show that M1 receptor activation also reduces the interaction of cortactin with Kv1.2 and that mutant Kv1.2 channels deficient for cortactin binding exhibit strongly attenuated ionic current. These results demonstrate a dynamic, phosphorylation-dependent interaction between Kv1.2 and the actin cytoskeleton-binding protein cortactin and suggest a role for that interaction in the regulation of Kv1.2 ionic current.Ion channels regulate a wide range of cellular processes, including development (1, 2), and neuronal plasticity (3, 4). Accordingly, the activity of nearly all ion channels is under some form of post-translational control, most commonly direct phosphorylation of the ion channel protein (5-7). The earliest and most widely reported examples involve serine/threonine phosphorylation; however, it is also now recognized that tyrosine phosphorylation is an important means of ion channel regulation (8). The nicotinic acetylcholine receptor was the first ligand-gated ion channel found to be regulated by tyrosine phosphorylation (9). The shaker family potassium channel Kv1.2, which is expressed abundantly in cardiac muscle (10) and neurons (11-13), was the first voltage-gated channel found to be so regulated.Kv1.2 ␣-subunit protein becomes tyrosine-phosphorylated upon the activation of M1 muscarinic acetylcholine receptors (mAChRs), 1 leading to a profound suppression of Kv1.2 ionic current (14). Part of the mechanism for such suppression involves phosphorylation of the N-terminal tyrosine Tyr 132 . However, phosphorylation of additional tyrosines within Kv1.2 is also likely to be required, since Y132F mutant channels are only partially resistant to tyrosine phosphorylation and ionic current suppression. Little is known about the signaling proteins involved in tyrosine phosphorylation-dependent suppression of Kv1.2 ionic current; however, binding of the activated form of the guanine nucleotide-binding protein RhoA to Kv1.2 is required (15).RhoA is an important regulator of actin dynamics (16 -18), and the physical association between RhoA and Kv1.2 suggests a link bet...

The repressor element 1 (RE1) silencing transcription factor (REST) in stem cells represses hundreds of genes essential to neuronal function. During neurogenesis, REST is degraded in neural progenitors to promote subsequent elaboration of a mature neuronal phenotype. Prior studies indicate that part of the degradation mechanism involves phosphorylation of two sites in the C terminus of REST that require activity of beta-transducin repeat containing E3 ubiquitin protein ligase, βTrCP. We identify a proline-directed phosphorylation motif, at serines 861/864 upstream of these sites, which is a substrate for the peptidylprolyl cis/trans isomerase, Pin1, as well as the ERK1/2 kinases. Mutation at S861/864 stabilizes REST, as does inhibition of Pin1 activity. Interestingly, we find that C-terminal domain small phosphatase 1 (CTDSP1), which is recruited by REST to neuronal genes, is present in REST immunocomplexes, dephosphorylates S861/864, and stabilizes REST. Expression of a REST peptide containing S861/864 in neural progenitors inhibits terminal neuronal differentiation. Together with previous work indicating that both REST and CTDSP1 are expressed to high levels in stem cells and down-regulated during neurogenesis, our results suggest that CTDSP1 activity stabilizes REST in stem cells and that ERK-dependent phosphorylation combined with Pin1 activity promotes REST degradation in neural progenitors.T he repressor element 1 (RE1) silencing transcription factor (REST) is a transcriptional repressor that suppresses neuronal gene expression in nonneural cells, such as fibroblasts, as well as in neural progenitors (1-3). Its targets represent genes required for the terminally differentiated neuronal cell phenotype, including genes encoding voltage and ligand-dependent ion channels, receptors, growth factors, and axonal-guidance proteins (4-7). Thus, during neurogenesis, REST is progressively down-regulated to allow elaboration of the mature neuronal phenotype (3). Nonetheless, precisely how REST itself is regulated still remains an open question. Relatively little is known about either its transcriptional or posttranscriptional regulation (3,8,9). In contrast, several studies have focused on posttranslational regulation of REST (3, 10, 11), but the identity of the signaling molecules involved has received little attention.In neural progenitors and human embryonic kidney (HEK) cells, rapid REST turnover is mediated by targeting to a proteasomal pathway (3, 10, 11). REST degradation during neuronal differentiation in culture requires interaction with beta-transducin repeat containing E3 ubiquitin protein ligase (βTrCP) for targeting to the proteasome (11). βTrCP was also required for cell-cycle-dependent degradation of REST in HEK cells (10). Two adjacent phosphorylated peptides in the C-terminal domain of REST were identified as βTrCP substrates in these studies, and function as degrons. One kinase responsible for the phosphorylation and degron activity in hippocampus is casein kinase 1, CK1 (12), but whether it function...

Infection with HIV or SIV often elicits a potent immune response to viral antigens. This includes T cells and antibodies specific for Gag and Env antigens. In contrast, when given as a vaccine, the same antigens have been weak immunogens, unable to elicit antibodies with comparable titer, durability, or neutralizing activity. We have used the live attenuated rubella vaccine strain RA27/3 as a viral vector to express HIV and SIV antigens. By mimicking an HIV infection, these vectors could elicit stronger and more durable immunity to HIV antigens. The vectors are based on the licensed rubella vaccine strain, which has demonstrated safety and potency in millions of children. One or two doses protect for life against rubella infection. The question was whether rubella vectors could similarly enhance the immunogenicity of a foreign vaccine insert. We have previously reported that rubella vectors can express small protein antigens in vitro and in vivo, where they elicit a strong immune response to the vaccine insert. The vectors have now expressed larger vaccine inserts that include epitope-rich fragments of the Gag matrix and capsid proteins (aa 41-211) or the complete p27 capsid protein with p2 (aa 136-381). These vectors have elicited a robust and durable immune response to Gag in rhesus macaques. This size range also encompasses the engineered outer domain (eOD) of HIV envelope gp120 (172 amino acids). The rubella/eOD-GT6 and GT8 vectors stably expressed glycoproteins that bind germline precursors and mature forms of VRC01-class broadly neutralizing antibodies. These vectors potentially could be used as part of a sequential immunization strategy to initiate the production of broadly neutralizing antibodies.

Neurogenesis begins in embryonic development and continues at a reduced rate into adulthood in vertebrate species, yet the signaling cascades regulating this process remain poorly understood. Plasma membrane-initiated signaling cascades regulate neurogenesis via downstream pathways including components of the transcriptional machinery. A nuclear factor that temporally regulates neurogenesis by repressing neuronal differentiation is the repressor element 1 (RE1) silencing transcription (REST) factor. We have recently discovered a regulatory site on REST that serves as a molecular switch for neuronal differentiation. Specifically, C-terminal domain small phosphatase 1, CTDSP1, present in non-neuronal cells, maintains REST activity by dephosphorylating this site. Reciprocally, extracellular signal-regulated kinase, ERK, activated by growth factor signaling in neural progenitors, and peptidylprolyl cis/trans isomerase Pin1, decrease REST activity through phosphorylation-dependent degradation. Our findings further resolve the mechanism for temporal regulation of REST and terminal neuronal differentiation. They also provide new potential therapeutic targets to enhance neuronal regeneration after injury.