Izuhara K, Sakai M, Inaba R, Imamura T, Howard M, Harada N
Department of Immunology, DNAX Research Institute of Molecular and Cellular Biology, Incorporated, Palo Alto, California 94304-1104, USA.
Cell Immunol. 1995 Jul;163(2):254-9. doi: 10.1006/cimm.1995.1124.
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)
我们之前已在人白细胞介素4受体（hIL-4R）的胞质结构域中确定了一个生长信号转导的关键区域。由于该受体的整个胞质结构域缺乏已知的催化活性，如酪氨酸激酶结构域，因此IL-4R很可能通过这个关键的胞质区域与其他信号转导分子结合。我们在此测试一种对应于这个关键胞质区域的合成肽，命名为SP-1，是否通过与IL-4R竞争结合细胞内信号转导分子来干扰IL-4诱导的增殖。我们的数据表明，100微克/毫升的SP-1肽完全抑制人IL-4（hIL-4）诱导的表达全长hIL-4R的Ba/F3转染细胞（hIL-4R-Ba/F3转染细胞）的增殖。相比之下，一种无关的合成肽，命名为SP-2，在很宽的浓度范围内都不影响hIL-4R-Ba/F3转染细胞中hIL-4诱导的增殖。SP-1和SP-2肽之间的这种差异并非由于它们被细胞摄取的差异，因为在使用放射性标记肽的实验中，胞质提取物中发现的SP-2肽比SP-1肽多约100倍。SP-1介导的对IL-4诱导增殖的抑制的特异性得到了以下事实的支持：SP-1肽对相同的hIL-4-Ba/F3转染细胞中IL-3诱导的增殖没有影响。此外，SP-1肽既不影响表达人白细胞介素2受体β链（hIL-2Rβ）的Ba/F3转染细胞中IL-2诱导的增殖，也不影响表达由hIL-4R胞外结构域和hIL-2Rβ胞质结构域组成的嵌合受体的Ba/F3转染细胞中hIL-4诱导的增殖。SP-1无法抑制其他IL-4反应性细胞系中IL-4诱导的增殖，如人红白血病细胞系TF-1和小鼠T细胞系HT2及CTLL-2。此外，SP-1仅对小鼠IL-4诱导的Ba/F3细胞增殖产生50%的抑制。SP-1在这些不同细胞系中未能抑制IL-4诱导的增殖，却能出色地抑制hIL-4R-Ba/F3转染细胞中hIL-4诱导的增殖，这似乎与每种细胞类型上表达的IL-4R数量有关。（摘要截短于400字）
