A synthetic peptide corresponding to a critical intracellular signaling region of the human IL-4 receptor inhibits IL-4-induced proliferation.
We have previously identified a critical region for growth signal transduction in the cytoplasmic domain of the human IL-4 receptor (hIL-4R). Since the entire cytoplasmic domain of this receptor lacks known catalytic activities such as the tyrosine kinase domain, it is likely that the IL-4R associates with other signal-transducing molecules through this critical cytoplasmic region. We test here whether a synthetic peptide corresponding to this critical cytoplasmic region, designated SP-1, interferes with IL-4-induced proliferation by competing with the IL-4R for binding to intracellular signal-transducing molecules. Our data indicated that 100 micrograms/ml SP-1 peptide completely inhibits human IL-4 (hIL-4)-induced proliferation of Ba/F3 transfectants expressing the full-length hIL-4R (hIL-4R-Ba/F3 transfectants). In contrast, a wide concentration range of an unrelated synthetic peptide, designated SP-2, did not affect hIL-4-induced proliferation of hIL-4R-Ba/F3 transfectants. This difference between SP-1 and SP-2 peptides was not due to their differential uptake by cell, since approximately 100 times more SP-2 peptide could be found in cytoplasmic extracts than SP-1 peptide in experiments using radiolabeled peptides. The specificity of SP-1-mediated inhibition of IL-4-induced proliferation was supported by the fact that the SP-1 peptide had no effect on IL-3-induced proliferation of the same hIL-4-Ba/F3 transfectants. In addition, the SP-1 peptide did not affect either IL-2-induced proliferation of Ba/F3 transfectants expressing the human IL-2 receptor beta chain (hIL-2R beta) or hIL-4-induced proliferation of Ba/F3 transfectants expressing a chimeric receptor consisting of the hIL-4R extracellular domain and the hIL-2R beta cytoplasmic domain. SP-1 was unable to inhibit IL-4-induced proliferation of other IL-4-responsive cell lines such as human erythroleukemic cell line TF-1 and mouse T cell lines HT2 and CTLL-2. In addition, SP-1 caused only a 50% inhibition of Ba/F3 cell proliferation induced by mouse IL-4. The failure of SP-1 to inhibit IL-4-induced proliferation in these various cell lines while producing excellent inhibition of hIL-4-induced proliferation of hIL-4R-Ba/F3 transfectants appeared to be related to the number of IL-4Rs expressed on each cell type.(ABSTRACT TRUNCATED AT 400 WORDS)
Izuhara
K
K
Department of Immunology, DNAX Research Institute of Molecular and Cellular Biology, Incorporated, Palo Alto, California 94304-1104, USA.
Sakai
M
M
Inaba
R
R
Imamura
T
T
Howard
M
M
Harada
N
N
D000595:Amino Acid Sequence; D002460:Cell Line; D007136:Immunoglobulins / Q000494:pharmacology; D015847:Interleukin-4 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D008969:Molecular Sequence Data; D018123:Receptors, Interleukin / Q000378:metabolism / Q000502:physiology*; D019948:Receptors, Interleukin-4; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000276:immunology; D014162:Transfection / Q000187:drug effects
D007136:Immunoglobulins; D018123:Receptors, Interleukin; D019948:Receptors, Interleukin-4; D011994:Recombinant Proteins; C090698:SP1 antigen; D015847:Interleukin-4