Inflammatory Signals Direct Expression of Human IL12RB1 into Multiple Distinct Isoforms

Abstract

IL12RB1 is essential for human resistance to multiple intracellular pathogens, including Mycobacterium tuberculosis. In its absence, the proinflammatory effects of the extracellular cytokines IL-12 and IL-23 fail to occur, and intracellular bacterial growth goes unchecked. Given the recent observation that mouse leukocytes express more than one isoform from il12rb1, we examined whether primary human leukocytes similarly express more than one isoform from IL12RB1. We observed that human leukocytes express as many as 13 distinct isoforms, the relative levels of each being driven by inflammatory stimuli both in vitro and in vivo. Surprisingly, the most abundant isoform present before stimulation is a heretofore uncharacterized intracellular form of the IL-12R (termed “isoform 2”) that presumably has limited contact with extracellular cytokine. After stimulation, primary PBMCs, including the CD4+, CD8+, and CD56+ lineages contained therein, alter the splicing of IL12RB1 RNA to increase the relative abundance of isoform 1, which confers IL-12/IL-23 responsiveness. These data demonstrate both a posttranscriptional mechanism by which cells regulate their IL-12/IL-23 responsiveness, and that leukocytes primarily express IL12RB1 in an intracellular form located away from extracellular cytokine.

IL12Rβ1ΔTM Is a Secreted Product ofil12rb1That Promotes Control of Extrapulmonary Tuberculosis

“…Preliminary experiments testing this possibility have thus far been inconclusive (data not shown); however, should IL12R␤1⌬TM function in trans, it raises the exciting possibility that recombinant IL12R␤1⌬TM could be used to boost both IL-12 responsiveness as part of a vaccine strategy. Although IL12R␤1⌬TM is expressed by both innate and adaptive lineages (24,26), our recent demonstration that il12rb1 gene products must be expressed by rag1-dependent lineages for TB control to occur (32) supports a model wherein T cell expression of IL12R␤1⌬TM, and not innate expression, is primarily responsible for IL12R␤1⌬TM's protective effects in extrapulmonary sites. Therefore, it will be important to understand IL12R␤1⌬TM's mechanism in the context of T H 1 cell biology and how the balance between IL12R␤1 and IL12R␤1⌬TM fine-tunes the T H 1 response, since this lineage is required for TB control (33).…”

“…Efforts are under way to identify the cis-elements in the human genome that direct preferential splicing of the various human IL12RB1 isoforms. Sequence variation in these elements may underlie why, between healthy individuals with otherwise identical IL12RB1 exon sequences, such wide variation in IL12RB1 splicing exists (26). Finally, the mechanism by which IL12R␤1⌬TM promotes IL12p40-dependent responses is likely distinct from that of IL12R␤1, a type I transmembrane protein that associates with the IL12p40 domain of IL-12, and signals in concert with IL12R␤2 (which binds the IL12p35 domain of IL-12).…”

“…IL12R␤1⌬TM is a product of il12rb1 alternative splicing that was first discovered by Chua et al upon cloning of the IL-12 receptor (25). IL12R␤1⌬TM is similar to IL12R␤1 in its retention of a signal peptide, cytokine-binding region, fibronectin domains (25,26), and expression by both innate and lymphocyte lineages (26). IL12R␤1⌬TM is dissimilar to IL12R␤1, however, in that it lacks a transmembrane domain, has an alternate C-terminal amino acid sequence, and localizes to an intracellular reticulum that resembles the endoplasmic reticulum (ER) (26).…”

“…IL12R␤1⌬TM is similar to IL12R␤1 in its retention of a signal peptide, cytokine-binding region, fibronectin domains (25,26), and expression by both innate and lymphocyte lineages (26). IL12R␤1⌬TM is dissimilar to IL12R␤1, however, in that it lacks a transmembrane domain, has an alternate C-terminal amino acid sequence, and localizes to an intracellular reticulum that resembles the endoplasmic reticulum (ER) (26). IL12R␤1⌬TM's characteristics make it similar to other cytokine receptor splice variants that pass through the ER prior to secretion (27); however, it has not yet been demonstrated that IL12R␤1⌬TM is a secreted protein.…”

The introduction of RNA-DNA differences underlies interindividual variation in the human IL12RB1 mRNA repertoire

“…IL12RB1 mRNA (isoform 1) was purified and amplified from PBMC and lung lysates, using our previously established protocols (23). gDNA from the same cell preparations was isolated using the DNeasy method (Qiagen); the primers and conditions used to amplify each IL12RB1 exon (17 total) are provided in Dataset S1.…”