The differential production of three forms of IL-1 receptor antagonist by human neutrophils and monocytes.
IL-1R antagonist (IL-1Ra) exists as three well-characterized isoforms. The 17-kDa secretory IL-1Ra (sIL-1Ra) and 18-kDa intracellular IL-1Ra (icIL-1RaI) arise by alternative transcription of the same IL-1Ra gene. The recently described 16-kDa intracellular IL-1Ra (icIL-1RaII) is formed by alternative translation initiation of sIL-1Ra mRNA. Transcription and translation of IL-1Ra isoforms were examined in LPS-stimulated human neutrophils and PBMC using RT-PCR, ELISA, and Western blot analysis. LPS stimulation of neutrophils resulted in elevated sIL-1Ra mRNA levels by 1 h, whereas icIL-1RaI mRNA remained undetectable through 22 h of culture. Extracellular glycosylated sIL-1Ra protein and intracellular icIL-1RaII were observed in LPS-stimulated neutrophils by 3 h of culture; no icIL-1RaI protein was detected by immunoblot. LPS stimulation of PBMC resulted in elevated sIL-1Ra mRNA levels by 1 h and detectable icIL-1RaI mRNA at 8 h of culture. LPS-stimulated PBMC demonstrated extracellular glycosylated sIL-1Ra protein and intracellular icIL-1RaII within 3 h of stimulation, whereas detection of icIL-1RaI protein was delayed until 15 h of culture. Subcellular localization experiments established that both icIL-1RaI and icIL-1RaII were present primarily within the cytoplasmic compartment, as expected by their lack of a signal peptide. These results demonstrate that although both LPS-stimulated neutrophils and PBMC synthesize sIL-1Ra and icIL-1RaII, only PBMC transcribe and translate icIL-1RaI. Furthermore, sIL-Ra transcription and translation (and translation of icIL-1RaII) are early events, whereas icIL-1RaI transcription in PBMC is delayed.
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
M
M
Malyak
M F
MF
Smith
A A
AA
Abel
K R
KR
Hance
W P
WP
Arend
D002478:Cells, Cultured; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D007424:Intracellular Fluid / Q000378:metabolism; D007536:Isomerism; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D009000:Monocytes / Q000378:metabolism*; D009504:Neutrophils / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D017472:Receptors, Interleukin-1 / Q000037:antagonists & inhibitors*; D012795:Sialoglycoproteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
C507763:IL1RN protein, human; D053590:Interleukin 1 Receptor Antagonist Protein; D012333:RNA, Messenger; D017472:Receptors, Interleukin-1; D012795:Sialoglycoproteins