TY - JOUR
T1 - Posttranslational regulation of Lck and a p36-38 protein by activators of protein kinase C
T2 - Differential effects of the tumor promoter, PMA, and the non-tumor-promoter, bryostatin
AU - Galron, Dalia
AU - Ansotegui, Ignacio J.
AU - Isakov, Noah
N1 - Funding Information:
1The work reported herein was supported, in part, by grants from the Israel Academy of Sciences and Humanities, the Chief Scientist's Of®ce, Israel Ministry of Health, the Israel Cancer Association, the Basque Goverenment, and an ICRF Career Development Award (N.I.).
PY - 1997/6/15
Y1 - 1997/6/15
N2 - T cell activation via the antigen receptor or by PKC-activating drugs results in phosphorylation of Lck and alteration of its electrophoretic mobility. Although tyrosine phosphorylation appears to regulate Lck enzymatic activity, the significance of phosphorylation of serine residues and its relevance to the cell proliferation process are yet unclear. We found that the PKC activator, bryostatin, like PMA, induced the conversion of p56(lck) to a slower migrating form with an apparent molecular mass of 60 kDa. The effect of PMA lasted over 48 hr but that of bryostatin was transient and correlated in time kinetics with that of the bryostatin-induced degradation of PKC. The effects of bryostatin were dominant over those of PMA. In addition, PKC was found to affect both serine and tyrosine phosphorylation of Lck but had no significant effect on the in vitro catalytic activity of Lck. To test whether serine phosphorylation of Lck may affect its ability to bind tyrosine phosphoproteins, we compared Lck immuno-precipitates from PMA- and bryostatin-treated T cells. We found that a 36-to 38-kDa tyrosine phosphoprotein co-immunoprecipitated with Lck from cells that were treated for 24 hr with PMA, but not bryostatin. A p36-38 from PMA- but not bryostatin-treated cells also interacted with an Lck-SH2 fusion protein, suggesting differential regulation of p36-38 by PMA and bryostatin. Furthermore, in vitro phosphorylation of p36-38 occurred in lysates of cells that were treated for 24 hr with PMA, but not in lysates of bryostatin- treated cells. The results show that tyrosine phosphorylation and the association of p36-38 with Lck are differentially affected by bryostatin and PMA and suggest that PKC regulates the interaction of potential signaling molecules with Lck, thereby regulating biochemical events that are relevant to T cell mitogenesis and/or transformation.
AB - T cell activation via the antigen receptor or by PKC-activating drugs results in phosphorylation of Lck and alteration of its electrophoretic mobility. Although tyrosine phosphorylation appears to regulate Lck enzymatic activity, the significance of phosphorylation of serine residues and its relevance to the cell proliferation process are yet unclear. We found that the PKC activator, bryostatin, like PMA, induced the conversion of p56(lck) to a slower migrating form with an apparent molecular mass of 60 kDa. The effect of PMA lasted over 48 hr but that of bryostatin was transient and correlated in time kinetics with that of the bryostatin-induced degradation of PKC. The effects of bryostatin were dominant over those of PMA. In addition, PKC was found to affect both serine and tyrosine phosphorylation of Lck but had no significant effect on the in vitro catalytic activity of Lck. To test whether serine phosphorylation of Lck may affect its ability to bind tyrosine phosphoproteins, we compared Lck immuno-precipitates from PMA- and bryostatin-treated T cells. We found that a 36-to 38-kDa tyrosine phosphoprotein co-immunoprecipitated with Lck from cells that were treated for 24 hr with PMA, but not bryostatin. A p36-38 from PMA- but not bryostatin-treated cells also interacted with an Lck-SH2 fusion protein, suggesting differential regulation of p36-38 by PMA and bryostatin. Furthermore, in vitro phosphorylation of p36-38 occurred in lysates of cells that were treated for 24 hr with PMA, but not in lysates of bryostatin- treated cells. The results show that tyrosine phosphorylation and the association of p36-38 with Lck are differentially affected by bryostatin and PMA and suggest that PKC regulates the interaction of potential signaling molecules with Lck, thereby regulating biochemical events that are relevant to T cell mitogenesis and/or transformation.
UR - http://www.scopus.com/inward/record.url?scp=0031570744&partnerID=8YFLogxK
U2 - 10.1006/cimm.1997.1120
DO - 10.1006/cimm.1997.1120
M3 - Article
AN - SCOPUS:0031570744
SN - 0008-8749
VL - 178
SP - 141
EP - 151
JO - Cellular Immunology
JF - Cellular Immunology
IS - 2
ER -