Specific Jak3 Downregulation in Lymphocytes Impairs γc Cytokine Signal Transduction and Alleviates Antigen-driven Inflammation In Vivo

Abstract

Jak3, one of the four members comprising the Jak family of cytosolic tyrosine kinases, has emerged as a promising target for nontoxic immunotherapies. Although a number of Jak inhibitors has already demonstrated efficacy, they suffer from secondary effects apparently associated to their pan-Jak activity. However, whether selective Jak3 inhibition would afford therapeutic efficacy remains unclear. To address this question we have investigated the immunosuppressive potential of selective Jak3 intervention in lymphocytes using RNA interference (RNAi) technology in vitro and in vivo. Using synthetic small interference RNA (siRNA) sequences we achieved successful transfections into human and mouse primary T lymphocytes. We found that Jak3 knockdown was sufficient to impair not only interleukin-2 (IL-2) and T cell receptor (TCR)-mediated cell activation in vitro, but also antigen-triggereds welling, inflammatory cell infiltration, and proinflammatory cytokine raise in vivo. Furthermore, Jak1 (which mediates γc cytokine signaling in conjunction with Jak3) cosilencing did not provide higher potency to the aforementioned immunosuppressant effects. Our data provides direct evidences indicating that Jak3 protein plays an important role in γc cytokine and antigen-mediated T cell activation and modulates Th1-mediated inflammatory disorders, all in all highlighting its potential as a target in immunosuppressive therapies.Molecular Therapy - Nucleic Acids (2012) 1, e42; doi:10.1038/mtna.2012.37; published online 04 September 2012.

Figure 1

Efficient small interference RNA (siRNA) transfection and target gene knockdown in human primary T lymphocytes. (a) Primary human T lymphocytes were incubated with 1 µmol/l Scrambled siRNA fluorescently labeled with FAM (FAM-Scr-siRNA) for 3 days. Fluorescence incorporation in Mock (empty histogram) and FAM-Scr-siRNA transfected T cells (green histogram) was assessed by flow cytometry. A representative histogram of four independent experiments is shown. (b) Cytoplasmatic localization of FAM-Scr-siRNA (green) sequence was confirmed by confocal microscopy. Cy3-CD3 (red) mAb was used as membrane marker. Nuclei were labeled with DRAQ5 (blue). A representative view of three independent experiments is shown. (c) JAK1 and (d) JAK3 mRNA content at day 3 (d3) and 7 (d7) post-transfection with 1 µmol/l indicated siRNA sequence was assessed by quantitative reverse transcription-PCR (RT-PCR). GUSb was used as housekeeping gene. Results are expressed as mean ± SEM relative to Mock; n = 3; ^&P < 0.001 versus Scr. (e) Western blot from protein extracts obtained on d3. A representative blot is shown. (f) Blots were quantified by subsequent densitometry. Results are expressed as mean ± SEM; n = 6–10; *P < 0.05; ^#P < 0.01; ^&P < 0.001 versus Scr. Two sequences (described in Materials and Methods section) were tested for each target, which performed equally (data not shown). Results are expressed as the mean values of the two sequences.

Figure 2

Single Jak depletion compromises the Jak-Stat signaling pathway. Human primary T lymphocytes were cultured in the absence (Ct) or presence of interleukin-2 (IL-2) stimulus during either Mock, Scrambled (Scr), Jak3, Jak1, or Jak1+Jak3 small interference RNA (siRNA) treatments at 1 µmol/l or 250 nmol/l. After 3 days, IL-2 signal transduction was evaluated. (a) Scheme of γc cytokine-mediated Jak-Stat pathway. (b) Jak1-P Tyr^1022–1023 and Jak3-P Tyr^980–981 were analyzed by western blot. Representative blot of six independent experiments is shown. (c) Densitometric analysis of blots obtained from cells treated with 1 µmol/l siRNA; (n = 6). (d) Densitometric analysis of blots obtained from cells treated with 250 nmol/l siRNA; (n = 4). Data are expressed as phospho-Jak/total Jak ratio relative to Mock treatment. (e) Stat5a/b phosphorylation was analyzed using the Luminex xMAP technology (n = 4). Data are expressed as phospho-Stat5a/b relative to nonstimulated control treatment (Ct). In addition, the expression of downstream targets genes as (f) suppressor of cytokine signaling 3 (SOCS3) (n = 4) and (g) B-cell leukemia/lymphoma 2 (BCL2) (n = 4) was examined. Gene expression was quantified by quantitative reverse transcription-PCR (RT-PCR). As housekeeping gene β-glucoronidase (GUSb) was used. Each value represents the mean relative amount of mRNA with respect to Mock treatment. (h) IL-2 induced interferon-γ (IFNγ) secretion was evaluated as IFNγ on the culture supernatant determined by enzyme-linked immunosorbent assay (ELISA) (n = 4). Data are expressed as mean ± SEM; *P < 0.05; ^#P < 0.01; ^&P < 0.001 versus Scr; ^§P < 0.05 versus Jak3 siRNA.

Figure 3

Jak3 and Jak1 are essential to maintain cell viability in interleukin-2 (IL-2) activated T lymphocytes. Human primary T lymphocytes were cultured in absence (Ct) or presence of IL-2 stimulus during either Mock or 1 µmol/l Scrambled (Scr), Jak3, Jak1, or Jak1+Jak3 small interference RNA (siRNA) treatments. (a) Cell viability was measured on day three (d3) and seven (d7) after siRNA incubation. Data are represented as mean ± SEM % viability versus control Mock group on d3. n = 8; *P < 0.05 and ^&P < 0.001. (b) Dose-response silencing in primary human T lymphocytes. Cells were treated with 500, 250, and 100 nmol/l indicated siRNA sequences. On d3 protein extracts were obtained and analyzed by western blot. A representative blot from at least three independent experiments is shown. (c) Cell viability was measured on d7 after 1,000 nmol/l (n = 8), 500 nmol/l (n = 5), 250 nmol/l (n = 8), or 100 nmol/l (n = 7) indicated siRNA sequences treatment. Data are expressed as mean ± SEM relative to control Mock group on d3. (d) Dead and/or apoptotic cell population secondary to Jak knockdown was assessed on d7 by cytometry using Alexa Fluor488-Annexin V and propidium iodide (PI) double staining. Death (AnnV⁺/PI⁺) and apoptotic (Annexin V⁺/PI) populations were quantified. As positive control for apoptotic stimulus (Ct+), cells were incubated with 1.5 µmol/l camptothecin for 24 hours. Data are expressed as mean ± SEM relative to Mock control group. n = 4; *P < 0.05; ^#P < 0.01; ^&P < 0.001 versus Scr.

Figure 4

Jak1 and Jak3 targeting equally impairs early T cell receptor (TCR) signaling events and cell activation in vitro. On day 3 after either Mock (empty bars) or 1 µmol/l Scrambled (dotted bars), Jak3 (black bars), Jak1 (light gray bars), or Jak3 +Jak1 (dark gray bars) small interference RNA (siRNA) treatments, human T lymphocytes were stimulated with CD3-CD28 mAb for 10 minutes. (a) Phospho-CD3ε and (b) phospho-CREB were detected using the Luminex xMAP system. Data are expressed as mean ± SEM relative phosphorylation versus non-CD3-CD28-stimulated control (Ct). n = 4, *P < 0.05; ^#P < 0.01 versus Scr. (c) Cellular viability was assessed before and 72 hours after CD3-CD28 challenge. Data are expressed as mean ± SEM relative to control Mock group before stimulus. n = 3, *P < 0.05; ^#P < 0.01; ^&P < 0.001 versus Scr.

Figure 5

Murine lymphocytes small interference RNA (siRNA) transfection setup and endogenous target silencing. (a) BALB/c Th1 cells were incubated in the absence (empty histogram) or presence of 1 µmol/l Scrambled ACCELL siRNA fluorescently labeled with CyTM3 (red histogram) for 3 days. On the third day, fluorescence incorporation was assessed by flow cytometry. A representative histogram of four independent experiments is shown. (b) Cytoplasmatic localization of CyTM3-labeled scrambled siRNA sequences (red) was confirmed by confocal microscopy in the same cells. FITC-CD3 mAb (green) was used as a T cell membrane marker. Nuclei were labeled with DRAQ5 (blue). A representative view of three independent experiments is shown. For silencing efficiency experiments, cells were left unstimulated (Th1-), or stimulated with Th1 cytokines during incubations in absence (Mock) or presence of 1 µmol/l Scrambled (Scr), mJak3 ormJak1 siRNA sequences. On the third day (c) jak1 and (d) jak3 mRNA levels were assessed by quantitative reverse transcription-PCR (RT-PCR). gusb was used as housekeeping gene. Data are expressed as mean ± SEM relative to nonstimulated cells (Th1-); n = 5; *P < 0.05 versus Scr; n.s.; nonsignificative; one-tailed Student's t-test.

Figure 6

Specific Jak3 knockdown alleviates inflammation in vivo. OVA-TCRtg stimulated Th1 cells were Mock, Scrambled small interference RNA (siRNA), mJak3 siRNA or mJak3+mJak1 siRNA transfected at 1 µmol/l each as stated in Materials and Methods section. After 72 hours, 5 × 10⁶ cells were adoptively transferred into naive syngeneic recipient mice. Twenty four hours after adoptive cell transfer, mice were challenged by s.c. injection of 5 µg OVA_323–339/incomplete Freund's adjuvant (IFA) emulsion in the right footpad. As a control, nonadoptively transferred naive mice were used (Ct). (a) Plasmatic interferon-γ (IFNγ) levels 24 hours after OVA_323–339 challenge were determined by enzyme-linked immunosorbent assay (ELISA). Data are mean ± SEM; n = 6; *P < 0.05 versus Scr. (b) Footpad swelling was measured 24 hours after challenge. Results were defined as % inflammation relative to the background in 0% control (Ct) and the 100% control (Mock), respectively. Data are mean ± SEM of 12 animals analyzed in two independent experiments. *P < 0.05; ^#P < 0.01 versus Scr. (c) Cell migration in the delayed type hypersensibility (DTH) test site was evaluated in hematoxylin-eosin stained sections from Mock (panels i), Scr (panel ii), and Jak3 groups (panels iii and iv). Representative images of five samples analyzed per group are shown. Arrows point to cellular infiltrate indicative of inflammation. Size bars represent 200 µm. (d) Histological score for inflamed footpads was awarded as stated in Material and Methods. n = 4–5; *P < 0.05, ^#P < 0.01, one tailed Student's t-test versus Scr. Finally, 24 hours after in vivo OVA_323–339 challenge, draining lymph node cells were collected and rechallenged in vitro with 10 µg/ml OVA_323–339 further 48 hours. At this point, proliferation and IFNγ secretion were evaluated. (e) Proliferation response was estimated as relative cell viability versus nonchallenged cells (0 µg/ml OVA_323–339) in each group. (f) Supernatant IFNγ was measured by enzyme-linked immunosorbent assay (ELISA). Data are mean ± SEM of 4–7 measurements from two independent experiments. *P < 0.05 versus Scr. TCR, T cell receptor.