Search

Abstract: Modulation on the duration of intracellular Ca2+ transients is essential for B-cell activation. We have previously shown that extracellular-signal-regulated kinase (ERK) can phosphorylate inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) at serine 436 and regulate its calcium channel activity. Here we investigate the potential physiological interaction between ERK and IP3R1 using chicken DT40 B-cell line in which different mutants are expressed. The interaction between ERK and IP3R1 is confirmed by co-immunoprecipitation and fluorescence resonance energy transfer (FRET) assays. This constitutive interaction is independent of either ERK kinase activation or IP3R1 phosphorylation status. Back phosphorylation analysis further shows that type 1 IP3R (IP3R1) is phosphorylated by ERK in anti-IgM-activated DT40 cells. Finally, our data show that the phosphorylation of Ser 436 in the IP3-binding domain of IP3R1 leads to less Ca2+ release from endoplasmic reticulum (ER) microsomes and accelerates the declining of calcium increase in DT40 cells in response to anti-IgM stimulation. [Copyright &y& Elsevier]

Abstract: Type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) is a widely expressed intracellular calcium-release channel found in many cell types. The operation of IP3R1 is regulated through phosphorylation by multiple protein kinases. Extracellular signal-regulated kinase (ERK) has been found involved in calcium signaling in distinct cell types, but the underlying mechanisms remain unclear. Here, we present evidence that ERK1/2 and IP3R1 bind together through an ERK binding motif in mouse cerebellum in vivo as well as in vitro. ERK-phosphorylating serines (Ser 436) was identified in mouse IP3R1 and Ser 436 phosphorylation had a suppressive effect on IP3 binding to the recombinant N-terminal 604-amino acid residues (N604). Moreover, phosphorylation of Ser 436 in R(224–604) evidently enhance its interaction with the N-terminal “suppressor” region (N223). At last, our data showed that Ser 436 phosphorylation in IP3R1 decreased Ca2+ releasing through IP3R1 channels. [Copyright &y& Elsevier]