Phosphorylation of phospholipase C-delta 1 regulates its enzymatic activity.
Phosphorylation of phospholipase C-delta(1) (PLC-delta(1)) in vitro and in vivo was investigated. Of the serine/threonine kinases tested, protein kinase C (PKC) phosphorylated the serine residue(s) of bacterially expressed PLC-delta(1) most potently. It was also demonstrated that PLC-delta(1) directly bound PKC-alpha via its pleckstrin homology (PH) domain. Using deletion mutants of PLC-delta(1) and synthetic peptides, Ser35 in the PH domain was defined as the PKC mediated in vitro phosphorylation site of PLC-delta(1). In vitro phosphorylation of PLC-delta(1) by PKC stimulated [(3)H]PtdIns(4,5)P(2) hydrolyzing activity and [(3)H]Ins(1,4,5)P(3)-binding of the PLC-delta(1). On the other hand, endogenous PLC-delta(1) was constitutively phosphorylated and phosphoamino acid analysis revealed that major phosphorylation sites were threonine residues in quiescent cells. The phosphorylation level and the species of phosphoamino acid were not changed by various stimuli such as PMA, EGF, NGF, and forskolin. Using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, we determined that Thr209 of PLC-delta(1) is one of the constitutively phosphorylated sites in quiescent cells. The PLC activity was potentiated when constitutively phosphorylated PLC-delta(1) was dephosphorylated by endogenous phosphatase(s) in vitro. Additionally, coexpression with PKC-alpha reduced serine phosphorylation of PLC-delta(1) detected by an anti-phosphoserine antibody and PLC-delta(1)-dependent basal production of inositol phosphates in NIH-3T3 cells, suggesting PKC-alpha activates phosphatase or inactivates another kinase involved in PLC-delta(1) serine phosphorylation to modulate the PLC-delta(1) activity in vivo. Taken together, these results suggest that PLC-delta(1) has multiple phosphorylation sites and phosphorylation status of PLC-delta(1) regulates its activity positively or negatively depends on the phosphorylation sites.
Fujii
Makoto
M
Graduate School of Life Science, University of Hyogo, Harima Science Garden City, Hyogo 678-1297, Japan.
Yi
Kye Sook
KS
Kim
Myung Jong
MJ
Ha
Sang Hoon
SH
Ryu
Sung Ho
SH
Suh
Pann-Ghill
PG
Yagisawa
Hitoshi
H
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D041681:NIH 3T3 Cells; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D054803:Phospholipase C delta / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011485:Protein Binding; D051571:Protein Kinase C-alpha / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism
D050505:Mutant Proteins; D010455:Peptides; D011993:Recombinant Fusion Proteins; D010768:Phosphoserine; D015544:Inositol 1,4,5-Trisphosphate; D051571:Protein Kinase C-alpha; D054803:Phospholipase C delta; C518026:Plcd1 protein, rat