CaMKII2 plays a ubiquitous and central role in calcium signaling. Alternative splicing of the four CaMKII genes (␣, ␤, ␥, and ␦) gives rise to ϳ30 known mRNA/protein products. CaMKII␣ and CaMKII␤ predominate in the brain and are involved in normal regulation of synaptic transmission (1-4). Calcium/calmodulin-dependent autophosphorylation at Thr 286 (numbered as in CaMKII␣) enhances the affinity for calcium/calmodulin and confers autonomous (calcium-independent) activity after calmodulin dissociates. Consequently, CaMKII is capable of integrating information conveyed by the amplitude, frequency, and duration of local calcium transients to which it is exposed. Autophosphorylation at Thr 305/306 occurs only in the absence of bound calcium/calmodulin and blocks subsequent calmodulin binding (reviewed in Ref. 5).Knock-in mutation of the Thr 286 or Thr 305/306 autophosphorylation sites in murine CaMKII␣ to Ala or Asp drastically alters some forms of hippocampal synaptic plasticity and disrupts spatial learning behaviors (reviewed in Ref. 6). The specificity of changes in synaptic responses to their dedicated inputs implies that postsynaptic actions of CaMKII, such as modulation of the trafficking and activity of AMPA-type glutamate receptors, are exquisitely regulated in a spatial and temporal manner (7-9).CaMKII interacts with other proteins that we refer to collectively as CaMKII-associated proteins (CaMKAPs). At postsynaptic sites, these include multiple subunits of the N-methyl-D-aspartate-type glutamate receptor (NMDA receptor) (10 -13), densin-180 (14, 15), ␣-actinin (15, 16), cyclin-dependent protein kinase 5 (16), synGAP␤ (17), and filamentous actin (18,19). However, specific contributions of each of these interactions to neuronal signaling and the regulation of synaptic plasticity remain unclear (reviewed in Refs. 7-9). To specifically address this issue, it is critical to have a thorough understanding of the molecular bases for these interactions and the factors regulating complex formation.Prior studies have identified dissimilar high affinity CaMKII-binding domains in the NR2B subunit of the NMDA receptor and in densin-180. These interactions are differentially regulated by calcium/calmodulinbinding, autophosphorylation at Thr 286 , and phosphorylation of the binding proteins (10, 11, 13-15, 20, 21). Moreover, densin-180 and NR2B do not compete with each other for binding to CaMKII (14). Interestingly, densin-180 makes an additional direct interaction with ␣-actinin (15), and ␣-actinin can bind to the NR1 and NR2B subunits of the NMDA receptor (21-24). However, little is known about the molecular determinants for CaMKII binding to ␣-actinin. Here, we report an initial molecular dissection of the CaMKII-binding domain in ␣-actinin-2 and explore the relationship of this interaction to CaMKII binding with densin-180 and NR2B. The data indicate that CaMKII itself may serve as a structural scaffold for the assembly of a postsynaptic signalosome. MATERIALS AND METHODSAntibodies-Western blotting was performed wit...

Cav1 (L-type) channels and calmodulin-dependent protein kinase II (CaMKII) are key regulators of Ca2+signaling in neurons. CaMKII directly potentiates the activity of Cav1.2 and Cav1.3 channels, but the underlying molecular mechanisms are incompletely understood. Here, we report that the CaMKII-associated protein densin is required for Ca2+-dependent facilitation of Cav1.3 channels. While neither CaMKII nor densin independently affects Cav1.3 properties in transfected HEK293T cells, the two together augment Cav1.3 Ca2+currents during repetitive, but not sustained, depolarizing stimuli. Facilitation requires Ca2+, CaMKII activation, and its association with densin, as well as densin binding to the Cav1.3 α1subunit C-terminal domain. Cav1.3 channels and densin are targeted to dendritic spines in neurons and form a complex with CaMKII in the brain. Our results demonstrate a novel mechanism for Ca2+-dependent facilitation that may intensify postsynaptic Ca2+signals during high-frequency stimulation.

The enzymes glutathione-S-transferases (GSTs, E.C.2.5.1.18) have been associated with detoxification of xenobiotics, limiting oxidative damage and other stress responses in plants. In this study, we report the isolation of a mustard gene, BjGSTF2, homologous to the phi class GSTs and changes in plant growth in vivo and shoot regeneration in vitro were related to GST expression. GST transcripts accumulated differentially in mustard organs, where transcript was most abundant in root. Tissues incubated at high temperature or in the presence of exogenous H2O2, HgCl2, 1-aminocyclopropane-1-carboxylate, salicylic acid and paraquat upregulated GST expression, whereas spermidine was inhibitory. To investigate the in vivo function of GST, transgenic Arabidopsis thalianaplants expressing sense (GST-S6), antisense (GST-A4) and double-stranded BjGSTF2 (GST-DS1) RNAs were generated. GST-S6 was shown to flower two days earlier and was relatively more tolerant to HgCl2 and paraquat, whereas GST-DS1 with least stress tolerance flowered one week later compared to WT and GST-A4. In shoot regeneration response, tissues originated from GST-S6 were highly regenerative, whereas no shoot regeneration was observed in GST-DS1 tissues after 30 days of culture. Results of this study provide the evidence showing that GST plays a role in plant growth and development in vivo and shoot regeneration in vitro.