Disparate intracellular processing of human IL-12 preprotein subunits: Atypical processing of the P35 signal peptide
Disparate intracellular processing of human IL-12 preprotein subunits: Atypical processing of the P35 signal peptide
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DOI：
10.4049/jimmunol.164.2.839
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发表时间：
2000-01-15
影响因子：
4.4
通讯作者：
Burd, PR
中科院分区：
文献类型：
--
作者：
Murphy, FJ;Hayes, MP;Burd, PR
IL-12是由APC产生的一种异源二聚体细胞因子，对细胞免疫起关键调节作用。由于IL-12在免疫应答中的关键作用，IL-12的产生受到严格的调控，部分是通过其p35亚基的转录控制，这需要干扰素-γ的分化效应才能表达，为了确定IL-12产生的转录后方面是否可能受到调控，我们研究了每个亚基的细胞内蛋白质处理，我们在这里报告p40和p35亚基是由不同的途径处理的。P40的加工符合信号肽去除伴随内质网(ER)转位的共翻译模型，而p35的加工则不符合。P35前蛋白转位到内质网并不伴随着信号肽的切割；相反，p35信号肽的去除是通过两次连续的切割进行的。第一次切割发生在内质网内，切割部位位于信号肽疏水区的中间，虽然前蛋白进入内质网时是糖基化的，但其糖基化状态并不影响初级切割。随后，p35信号肽的剩余部分被第二次切割去除，可能涉及金属蛋白酶，伴随着额外的糖基化和分泌。第二裂解位点突变或糖基化抑制可抑制p40的分泌，而糖基化抑制则不影响p40的分泌。我们的发现表明，IL-12亚单位是由不同的途径处理的，并为调节IL-12的产生提出了新的模式。
IL-12 is a heterodimeric cytokine produced by APC that critically regulates cell-mediated immunity. Because of its crucial function during immune responses, IL-12 production is stringently regulated, in part through transcriptional control of its p35 subunit, which requires the differentiative effects of IFN-gamma for expression, To determine whether post-transcriptional aspects of IL-12 production might be regulated, we examined intracellular protein processing of each subunit, We report here that p40 and p35 subunits are processed by disparate pathways. Whereas processing of p40 conforms to the cotranslational model of signal peptide removal concomitant with translocation into the endoplasmic reticulum (ER), processing of p35 does not. Translocation of the p35 preprotein into the ER was not accompanied by cleavage of the signal peptide; rather, removal of the p35 signal peptide occurred via two sequential cleavages. The first cleavage took place within the ER, and the cleavage site localized to the middle of the hydrophobic region of the signal peptide, Although the preprotein was glycosylated upon entry into the ER, its glycosylation status did not affect primary cleavage. Subsequently, the remaining portion of the p35 signal peptide was removed by a second cleavage, possibly involving a metalloprotease, concomitant with additional glycosylation and secretion. Secretion could be inhibited by mutation of the second cleavage site or by inhibition of glycosylation,vith tunicamycin, In contrast, p40 secretion was not affected by inhibition of glycosylation. Our findings demonstrate that IL-12 subunits are processed by disparate pathways and suggest new modalities for regulation of IL-12 production.