Rat basophiliv leukemia cells as model system for inositol 1,4,5-trisphosphate receptor IV, a receptor of the type II family: functional comparison and immunological detection (original) (raw)
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Molecular properties of inositol 1,4,5-trisphosphate receptors
Cell Calcium, 1999
The receptors for the second messenger inositol 1,4,5-trisphosphate (IP3) constitute a family of Ca2+ channels responsible for the mobilization of intracellular Ca2+ stores. Three different gene products (types I-III) have been isolated, encoding polypeptides which assemble as large tetrameric structures. Recent molecular studies have advanced our knowledge about the structure, regulation and function of IP3 receptors. For example, several Ca(2+)-binding sites and a Ca(2+)-calmodulin-binding domain have been mapped within the type I IP3 receptor, and studies on purified cerebellar IP3 receptors propose a second Ca(2+)-independent calmodulin-binding domain. In addition, minimal requirements for the binding of immunophilins and the formation of tetramers have been identified. Overexpression of IP3 receptors has provided further clues to the regulation of individual IP3 receptor isoforms present within cells, and the role that they play in the generation of IP3-dependent Ca2+ signals. Inhibition of IP3 receptor function and expression, and analysis of mutant IP3 receptors, suggests that IP3 receptors are involved in such diverse cellular processes as proliferation and apoptosis and are thus, necessary for normal development. Our understanding of the complex spatial and temporal nature of cytosolic Ca2+ increases and the role that these Ca2+ signals play in cell function depend upon our knowledge of the structure and the regulation of IP3 receptors. This review focuses on the molecular properties of these ubiquitous intracellular Ca2+ channels.
Proceedings of the National Academy of Sciences of the United States of America, 1992
Three inositol 1,4,5-trisphosphate receptor (IP3R) cDNAs, designated IP3R-II, -III, and -IV, were cloned from a mouse placenta cDNA library. All three display strong homology in membrane-spanning domains M7 and M8 to the originally cloned cerebellar IP3R-I, with divergences predominantly in cytoplasmic domains. Levels of mRNA for the three additional IP3Rs in general are substantially lower than for IP3R-I, though in the gastrointestinal tract the levels of IP3R-III may be comparable to IP3R-I. Cerebellar Purkinje cells express at least two and possibly three distinct IP3Rs, suggesting heterogeneity of IP3 action within a single cell.
The Biochemical journal, 1996
InsP3 receptor (InsP3R)/Ca(2+)-release channels differ markedly in abundance in different tissues/cell types and InsP3R expression levels may be modulated in response to a variety of external cues. Cell lines overexpressing InsP3Rs will provide useful models for the study of the influence of receptor density and subtype on InsP3-mediated Ca2+ signalling. We have investigated the properties of InsP3Rs in mouse L fibroblast cell lines transfected with either type-1 InsP3R cDNA (L15) or vector control (Lvec). L15 cells express approximately eightfold higher levels of the type-1 InsP3R protein than Lvec cells, as assessed by radioligand binding and immunoblotting. Increased expression was stable since it did not alter over ten cell passages. Both L15 and Lvec cells express predominantly the type-1 InsP3R isoform, indicating that functional differences in the InsP3-mediated Ca2+ signalling in these cell lines are due to alteration in the levels of receptor rather than changes in the isof...
The Journal of General Physiology, 1998
The inositol (1,4,5)-trisphosphate receptor (InsP3R) mediates Ca2+release from intracellular stores in response to generation of second messenger InsP3. InsP3R was biochemically purified and cloned, and functional properties of native InsP3-gated Ca2+channels were extensively studied. However, further studies of InsP3R are obstructed by the lack of a convenient functional assay of expressed InsP3R activity. To establish a functional assay of recombinant InsP3R activity, transient heterologous expression of neuronal rat InsP3R cDNA (InsP3R-I, SI− SII+ splice variant) in HEK-293 cells was combined with the planar lipid bilayer reconstitution experiments. Recombinant InsP3R retained specific InsP3binding properties (Kd= 60 nM InsP3) and were specifically recognized by anti–InsP3R-I rabbit polyclonal antibody. Density of expressed InsP3R-I was at least 20-fold above endogenous InsP3R background and only 2–3-fold lower than InsP3R density in rat cerebellar microsomes. When incorporated i...
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