Sequence and functional characterization of a third inositol trisphosphate receptor subtype, IP3R-3, expressed in pancreatic islets, kidney, gastrointestinal tract, and other tissues.
Inositol 1,4,5-trisphosphate (IP3) functions as a second messenger for many neurotransmitters, hormones and growth factors. It causes the release of Ca2+ from intracellular stores by binding to specific receptors that are coupled to Ca2+ channels. Recent studies have shown that there is a family of IP3 receptors, and the complete sequences of two members of this family and partial sequences of two others have been reported. We have determined the complete sequence of a third IP3 receptor, designated IP3R-3, and characterized its pharmacological properties and sites of expression. Rat IP3R-3 is 2670 amino acids in size, has 62 and 64% identity with IP3R-1 and IP3R-2, and is predicted to have a similar structure including a region of eight potential membrane-spanning segments at its COOH terminus, which presumably functions as a Ca2+ channel. Expression of recombinant rat IP3R-3 in COS-7 cells showed that it bound IP3 as well as inositol 1,3,4,5-tetrakisphosphate and inositol hexakisphosphate. Immunohistocytochemical studies of cells expressing recombinant IP3R-3 indicated that it has a preferential cellular distribution in the endoplasmic reticulum. RNA and protein blotting studies indicate that IP3R-3 is expressed in a number of different cultured cell lines including insulin-secreting RINm5F cells. The IP3R-3 is also expressed in adult pancreatic islets, kidney, gastrointestinal tract, and brain. Reverse transcriptase-polymerase chain reaction amplification of IP3R-1, -2, and -3 mRNAs in adult rat pancreatic islets indicated that IP3R-3 was the predominant subtype expressed in this tissue and thus may be responsible for mediating the effects of IP3 on insulin secretion.
Blondel
O
O
Howard Hughes Medical Institute, University of Chicago, Illinois 60637.
Takeda
J
J
Janssen
H
H
Seino
S
S
Bell
G I
GI
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015220:Calcium Channels; D002460:Cell Line; D003001:Cloning, Molecular; D004064:Digestive System / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D007150:Immunohistochemistry; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007515:Islets of Langerhans / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009838:Oligodeoxyribonucleotides; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D018160:Receptors, Cytoplasmic and Nuclear; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate