Endogenously Bound Calmodulin Is Essential for the Function of the Inositol 1,4,5-Trisphosphate Receptor

Abstract

Calmodulin (CaM) is a ubiquitous Ca2؉ sensor protein that plays an important role in regulating a large number of Ca 2؉ channels, including the inositol 1,4,5-trisphosphate receptor (IP 3 R). Despite many efforts, the exact mechanism by which CaM regulates the IP 3 R still remains elusive. Here we show, using unidirectional 45 (17). This can be explained by the large conformational change that the IP 3 R undergoes in the presence of Ca 2ϩ and which may be necessary for CaM action. This interaction may provide a tonic regulation of IP 3 R activity and can explain the low sensitivity of the IP 3 R in neuronal tissues where CaM is highly expressed. The role of the Ca 2ϩ -dependent CaM-binding site in the regulatory domain, however, still remains to be elucidated.CaM-binding sites have not merely been identified as regulatory sites but have also recently been implicated in inter-and intrasubunit interactions. For example, the CaM-binding domain of the RyR1 modulates channel activity by at least two mechanisms: 1) by direct binding of CaM and 2) by forming a bridge between two different regions on the RyR1. Peptides of the RyR1 were used to demonstrate that the CaM-binding region is indeed directly involved in intersubunit interactions between the RyR subunits (18). In the case of small conductance K ϩ channels, CaM is involved in intersubunit interactions. Functional small conductance K ϩ channels are heteromeric complexes with CaM, which is constitutively associated with the ␣-subunits in a Ca 2ϩ -independent manner (19). In this study, we investigated whether endogenously bound CaM is essential for IP 3 R functioning. To test this hypothesis, we measured IP 3 R activity in the presence of different synthetic peptides corresponding to the CaM-binding region of myosin light-chain kinase (MLCK), which has a very high affinity for CaM, and in the presence of peptides corresponding to CaM-binding sites of the IP 3 R and other

The Calponin Homology Domain of Vav1 Associates with Calmodulin and Is Prerequisite to T Cell Antigen Receptor-induced Calcium Release in Jurkat T Lymphocytes

“…6A, right panel). As reported previously, CaM antagonists (such as W-7) or high affinity CaM-binding peptides strongly inhibited IP 3 -induced Ca 2ϩ release (29,42). Therefore, by using intact cells and virally reconstituted cells, we tested the effects of Vav1 and Vav1⌬CH on Ca 2ϩ release by the inhibition of CaM.…”

“…CaM came to the scene as it was demonstrated to ubiquitously bind and regulate IP 3 R (29,(42)(43)(44). CaM pulldown assay was performed by incubating CaM-conjugated agarose with cell lysates of Jurkat or J.Vav1, respectively, or using plain agarose beads as a negative control.…”

“…Section 1734 solely to indicate this fact. 1 Ca 2ϩ -dependent association of CaM to IP 3 R is necessary for normal calcium release (29).…”

IP3 Receptors: Toward Understanding Their Activation

“…This evidence and the absence of the site from IP 3 R3 suggest that the central Ca 2þ -CaM-binding site cannot be responsible for Ca 2þ inhibition of IP 3 R. An additional high-affinity Ca 2þ -CaMbinding site is created in IP 3 R1 after removal of the S2 splice region: While this may increase the Ca 2þ -CaM sensitivity of peripheral S2 2 IP 3 R1, it is not a universal candidate for mediating Ca 2þ inhibition of IP 3 R (Islam et al 1996;Lin et al 2000). Recently, it was suggested that bound CaM is essential for IP 3 R function because a peptide antagonist of CaM inhibited IP 3 -evoked Ca 2þ release (Nadif Kasri et al 2006). It is now clear that this peptide acts directly on IP 3 R, with no requirement for CaM (Sun and Taylor 2008).…”

Vav Protein Guanine Nucleotide Exchange Factor Regulates CD36 Protein-mediated Macrophage Foam Cell Formation via Calcium and Dynamin-dependent Processes

“…4B), suggesting the possible involvement of PLC-␥1 activity in this process. Because Ca 2ϩ -dependent association of calmodulin (CaM) with the inositol trisphosphate (IP 3 ) receptor can regulate calcium release from intracellular stores (33) and because the calponin homology domain of Vav1 has been shown to interact with CaM in T cells (17), we also assessed uptake and binding of NO 2 LDL in the presence of TFP, a specific CaM inhibitor (Fig. 4B).…”