Regulation of Ca(2+) release through inositol 1,4,5-trisphosphate receptors (InsP(3)R) has important consequences for defining the particular spatio-temporal properties of intracellular Ca(2+) signals. In this study, regulation of Ca(2+) release by phosphorylation of type 1 InsP(3)R (InsP(3)R-1) was investigated by constructing "phosphomimetic" charge mutations in the functionally important phosphorylation sites of both the S2+ and S2- InsP(3)R-1 splice variants. Ca(2+) release was investigated following expression in Dt-40 3ko cells devoid of endogenous InsP(3)R. In cells expressing either the S1755E S2+ or S1589E/S1755E S2- InsP(3)R-1, InsP(3)-induced Ca(2+) release was markedly enhanced compared with nonphosphorylatable S2+ S1755A and S2- S1589A/S1755A mutants. Ca(2+) release through the S2- S1589E/S1755E InsP(3)R-1 was enhanced approximately 8-fold over wild type and approximately 50-fold when compared with the nonphosphorylatable S2- S1589A/S1755A mutant. In cells expressing S2- InsP(3)R-1 with single mutations in either S1589E or S1755E, the sensitivity of Ca(2+) release was enhanced approximately 3-fold; sensitivity was midway between the wild type and the double glutamate mutation. Paradoxically, forskolin treatment of cells expressing either single Ser/Glu mutation failed to further enhance Ca(2+) release. The sensitivity of Ca(2+) release in cells expressing S2+ S1755E InsP(3)R-1 was comparable with the sensitivity of S2- S1589E/S1755E InsP(3)R-1. In contrast, mutation of S2+ S1589E InsP(3)R-1 resulted in a receptor with comparable sensitivity to wild type cells. Expression of S2- S1589E/S1755E InsP(3)R-1 resulted in robust Ca(2+) oscillations when cells were stimulated with concentrations of alpha-IgM antibody that were threshold for stimulation in S2- wild type InsP(3)R-1-expressing cells. However, at higher concentrations of alpha-IgM antibody, Ca(2+) oscillations of a similar period and magnitude were initiated in cells expressing either wild type or S2- phosphomimetic mutations. Thus, regulation by phosphorylation of the functional sensitivity of InsP(3)R-1 appears to define the threshold at which oscillations are initiated but not the frequency or amplitude of the signal when established.
"InsP 3 R1 is phosphorylated by multiple protein kinases, including PKA (protein kinase A). Phosphorylation by PKA sensitises InsP 3 R1 to activation by InsP 3, both in vitro and in intact cells (Tang et al., 2003; Wagner et al., 2004). As a second messenger activating PKA, cAMP, similar to InsP 3 /Ca 2+ , regulates many cellular processes . "
[Show abstract][Hide abstract] ABSTRACT: Interconnections between the Ca2+ and cAMP signalling pathways can determine the specificity and diversity of the cellular effects mediated by these second messengers. Most cAMP effects are mediated by PKA (protein kinase A), which is anchored close to its membranous substrates by AKAPs (A kinase-anchoring proteins). In many cell types, the activation of InsP3R (inositol 1,4,5-trisphosphate receptor), an endoplasmic reticulum Ca2+ channel, is a key event of Ca2+ signalling. The phosphorylation of InsP3R1 by PKA stimulates Ca2+ mobilization. This control is thought to be tight, involving the association of PKA with InsP3R1. The InsP3R1 isoform predominates in central nervous tissue and its concentration is highest in the cerebellar microsomes. We investigated the complex formed by InsP3R1 and PKA in this fraction, vith a view to identifying its components and determining its distribution in the cerebellar cortex.
Immunoprecipitation experiments showed that InsP3R1 associated with PKA type IIbeta and AKAP450, the longer variant of AKAP9, in sheep cerebellar microsomes. The co-purification of AKAP450 with InsP3R1 on heparin-agarose provided further evidence of the association of these proteins. Immunohistofluorescence experiments on slices of cerebellar cortex showed that AKAP450 was colocalized with InsP3R1 and RIIbeta (regulatory subunit of PKA IIbeta) in granule cells, but not in Purkinje cells. AKAP450 was localized in the Golgi apparatus of these two cell types whereas InsP3R1 was detected in this organelle only in granule cells.
Taken together these results suggest that InsP3R1 forms a complex with AKAP450 and PKAIIbeta, localized in the Golgi apparatus of cerebellar granule cells. In contrast, the association of InsP3R1 with PKA in Purkinje cells would require a different macromolecular complex.
Biology of the Cell 03/2009; 101(8):469-80. DOI:10.1042/BC20080184 · 3.51 Impact Factor
"In contrast, substitution of phosphorylated S/T and Y residues with neutral or basic amino acids are considered to function as silencing substitutions (Wang and Klemke, 2008). Consequently, these two classes of mutations are often used to evaluate the role of S/T and Y protein phosphorylation in eukaryotes (for examples, see Fillebeen et al., 2003; Wagner et al., 2004; Lauberth et al., 2007; Onischenko et al., 2007). "
[Show abstract][Hide abstract] ABSTRACT: All living organisms communicate with the external environment for their survival and existence. In prokaryotes, communication is achieved by two-component systems (TCS) comprising histidine kinases and response regulators. In eukaryotes, signalling is accomplished by serine/threonine and tyrosine kinases. Although TCS and serine/threonine kinases coexist in prokaryotes, direct cross-talk between these families was first described in Group B Streptococcus (GBS). A serine/threonine kinase (Stk1) and a TCS (CovR/CovS) co-regulate toxin expression in GBS. Typically, promoter binding of regulators like CovR is controlled by phosphorylation of the conserved active site aspartate (D53). In this study, we show that Stk1 phosphorylates CovR at threonine 65. The functional consequence of threonine phosphorylation of CovR in GBS was evaluated using phosphomimetic and silencing substitutions. GBS encoding the phosphomimetic T65E allele are deficient for CovR regulation unlike strains encoding the non-phosphorylated T65A allele. Further, compared with wild-type or T65A CovR, the T65E CovR is unable to bind promoter DNA and is decreased for phosphorylation at D53, similar to Stk1-phosphorylated CovR. Collectively, we provide evidence for a novel mechanism of response regulator control that enables GBS (and possibly other prokaryotes) to fine-tune gene expression for environmental adaptation.
" AA InsP 3 R - 1 . C , WT InsP 3 R - 1 following addition of forskolin . D , EE InsP 3 R - 1 . The τ derived under these various conditions was unaltered . we monitored activity following activation of adenylate cyclase or by using InsP 3 R - 1 constructs which have been engineered to be either PKA non - phosphorylatable or mimic phosphorylation ( Wagner et al . 2003 , 2004 ) . These complimentary protocols clearly illustrate the power of the experimental system . In the former experiments , the measurement of PM InsP 3 R - 1 activity in the whole cell mode of the patch clamp technique allows the activation of endogenous PM signalling pathways resulting in PKA activation . The latter experiments , however "
[Show abstract][Hide abstract] ABSTRACT: Phosphorylation of inositol 1,4,5-trisphosphate receptors (InsP(3)R) by PKA represents an important, common route for regulation of Ca(2+) release. Following phosphorylation of the S2 splice variant of InsP(3)R-1 (S2-InsP-1), Ca(2+) release is markedly potentiated. In this study we utilize the plasma membrane (PM) expression of InsP(3)R-1 and phosphorylation state mutant InsP(3)R-1 to study how this regulation occurs at the single InsP(3)R-1 channel level. DT40-3KO cells stably expressing rat S2- InsP(3)R-1 were generated and studied in the whole-cell mode of the patch clamp technique. At hyperpolarized holding potentials, small numbers of unitary currents (average approximately 1.7 per cell) were observed which were dependent on InsP(3) and the presence of functional InsP(3)R-1, and regulated by both cytoplasmic Ca(2+) and ATP. Raising cAMP markedly enhanced the open probability (P(o)) of the InsP(3)R-1 and induced bursting activity, characterized by extended periods of rapid channel openings and subsequent prolonged refractory periods. The activity, as measured by the P(o) of the channel, of a non-phosphorylatable InsP(3)R-1 construct (Ser1589Ala/Ser1755Ala InsP(3)R-1) was markedly less than wild-type (WT) InsP(3)R-1 and right shifted some approximately 15-fold when the concentration dependency was compared to a phosphomimetic construct (Ser1589Glu/Ser1755Glu InsP(3)R-1). No change in conductance of the channel was observed. This shift in apparent InsP(3) sensitivity occurred without a change in InsP(3) binding or Ca(2+) dependency of activation or inactivation. Biophysical analysis indicated that channel activity can be described by three states: an open state, a long lived closed state which manifests itself as long interburst intervals, and a short-lived closed state. Bursting activity occurs as the channel shuttles rapidly between the open and short-lived closed state. The predominant effect of InsP(3)R-1 phosphorylation is to increase the likelihood of extended bursting activity and thus markedly augment Ca(2+) release. These analyses provide insight into the mechanism responsible for augmenting InsP(3)R-1 channel activity following phosphorylation and moreover should be generally useful for further detailed investigation of the biophysical properties of InsP(3)R.
The Journal of Physiology 07/2008; 586(Pt 15):3577-96. DOI:10.1113/jphysiol.2008.152314 · 5.04 Impact Factor
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