title: Regulation of phospholipase C-beta 4 by ribonucleotides and the alpha subunit of Gq.
abstract: The fourth member of mammalian beta-type phospholipase C isozymes, PLC-beta 4, was recently purified from bovine retina, and the corresponding cDNA was cloned from rat brain and sequenced. PLC-beta 4 has now been shown to differ from the other three mammalian beta-type isozymes (PLC-beta 1, -beta 2, and -beta 3) in that it is selectively inhibited by ribonucleotides. The inhibition requires the 5'-phosphate and 2'-hydroxyl groups of ribose as well as the base moiety. Thus, deoxyribonucleotides and ribose 5-phosphate were not inhibitory. The monophosphate, diphosphate, and triphosphate nucleoside derivatives were all inhibitory, whereas cyclic nucleotides were ineffective. Purine nucleotides were more potent inhibitors than pyrimidine nucleotides; the 50% inhibitory concentrations were 20-30 microM for AMP and GMP, and 100-200 microM for UMP and CMP. Unlike the other beta-type isozymes, PLC-beta 4 contains the GX4GKS consensus sequence for the recognition of the phosphoryl group of nucleotides. In the absence of ribonucleotides, the specific activity of PLC-beta 4 toward phosphatidyl-inositol 4,5-bisphosphate was four to five times the average specific activity of PLC-beta 1 and PLC-beta 3. Thus, nucleotide-dependent inhibition may serve to reduce the activity of PLC-beta 4 in the absence of a hormonal signal. The regulation of PLC-beta 4 by G-proteins was also studied. Similar to the other three PLC-beta isozymes, PLC-beta 4 was activated by the alpha subunit of Gq but not by the transducin alpha subunit. However, unlike other PLC-beta isozymes, PLC-beta 4 was not responsive to activation by G beta gamma subunits.
authors.affiliation: Laboratory of Biochemistry, NHLBI, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: C W
authors.initials: CW
authors.lastname: Lee
authors.forename: K H
authors.initials: KH
authors.lastname: Lee
authors.forename: S B
authors.initials: SB
authors.lastname: Lee
authors.forename: D
authors.initials: D
authors.lastname: Park
authors.forename: S G
authors.initials: SG
authors.lastname: Rhee
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D054799:Phospholipase C beta; D011487:Protein Conformation; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012265:Ribonucleotides / Q000494:pharmacology*; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D015293:Transducin / Q000378:metabolism; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; D012265:Ribonucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010738:Type C Phospholipases; D054799:Phospholipase C beta; C518038:Plcb2 protein, rat; C518041:Plcb3 protein, rat; D019204:GTP-Binding Proteins; D015293:Transducin