Differential regulation of phospholipase Cgamma subtypes through FcepsilonRI, high affinity IgE receptor.
The high affinity IgE receptor (FcepsilonRI) usually exists as a tetramer composed of alphabetagamma2 subunits. The COOH-tail of beta and gamma subunits contains consensus sequence termed 'immunoreceptor tyrosine-based activation motif' (ITAM). Tyrosine phosphorylated ITAM interacts with signaling proteins that contain the Src homology domain, forming a main amplifying and signaling route for FcepsilonRI. Unlike the COOH-tail, the functional role of NH(2)-tail of beta subunit in the signaling of FcepsilonRI is not clear because it lacks the ITAM sequences. To study the roles of NH(2)-tail of beta subunit, the cDNA library of RBL-2H3 cells was screened by yeast two-hybrid assay, and the NH(2)-tail of the beta subunit was found to interact with phospholipase Cgamma2 (PLCgamma2) but not with PLCgamma1. Since both PLCgamma1 and PLCgamma2 are expressed in RBL-2H3 cells and they possess identical cellular functions, the functional meaning of the protein-protein interaction between PLCgamma2 and NH(2)-tail of beta subunit was studied by comparing the regulatory pathways that control the FcepsilonRI-mediated tyrosine phosphorylation of the two enzymes. Our study shows that PI3-kinase and PMA-sensitive PKCs were required exclusively for the FcepsilonRI-mediated tyrosine phosphorylation of PLCgamma1. Also the FcepsilonRI-mediated tyrosine phosphorylation of PLCgamma1 was more sensitive to the inhibitors of Src and Syk kinases. These results therefore suggest that PLCgamma1 is involved in dynamic regulation of protein kinase C activity and inositol triphosphate levels in response to cellular needs. In contrast, PLCgamma2, through continuous interaction with the NH(2)-tail of beta subunit, co-localizes with FcepsilonRI in the same signaling domain, and maintains the basal cellular PLC activity.
Yoon
Eunju
E
Department of Pharmacology, College of Pharmacy, Chonnam National University, Kwang-Ju 500-757, Republic of Korea.
Beom
Sunryeo
S
Cheong
Ho
H
Kim
Soyoung
S
Oak
Minho
M
Cho
Dongim
D
Kim
Kyeong-Man
KM
D000818:Animals; D002460:Cell Line; D015971:Gene Expression Regulation, Enzymologic; D007073:Immunoglobulin E / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017455:Receptors, IgE / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D010738:Type C Phospholipases / Q000235:genetics / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D007527:Isoenzymes; D021122:Protein Subunits; D017455:Receptors, IgE; D007073:Immunoglobulin E; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D013755:Tetradecanoylphorbol Acetate