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.
Howard Hughes Medical Institute, University of Chicago, Illinois 60637.
O
O
Blondel
J
J
Takeda
H
H
Janssen
S
S
Seino
G I
GI
Bell
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