The molecular basis of IL-21–mediated proliferation

Abstract

Interleukin-21 (IL-21 IntroductionIL-21 is produced mainly by activated CD4 ϩ T cells and regulates functions of T, B, natural killer (NK), and myeloid cells. IL-21 signaling requires the heterodimerization of the IL-21R and ␥ c cytoplasmic domains. 1,2 ␥ c is also shared by the receptors for IL-2, IL-4, IL-7, IL-9, and IL-15, and is mutated in patients with X-linked severe combined immunodeficiency (XSCID), a disease in which T and NK cells are absent and B cells are not functional. 3 Defective IL-21 signaling contributes to the intrinsic B-cell defect in XSCID. 4,5 Il21r Ϫ/Ϫ mice have diminished IgG1 but elevated IgE levels in response to antigen, whereas Il21r Ϫ/Ϫ /Il4 Ϫ/Ϫ double knock-out mice exhibit a pan-hypogammaglobulinemia similar to what is found in XSCID, indicating a cooperative role for IL-4 and IL-21 in Ig production. 4 Depending on the stimulation context, IL-21 can be proapoptotic for B cells [6][7][8] or can promote their differentiation to memory and plasma cells. 7,9 IL-21 can also potently augment T-cell proliferation as a comitogen 10 and cooperates with IL-7 or IL-15 to drive the proliferation of resting CD8 ϩ T cells. 11 It can also augment NK-cell activity [12][13][14][15][16] and exert actions on dendritic cells (DCs) 17 and monocytes/macrophages. 18 Furthermore, IL-21 has been reported to have antitumor effects in a range of model systems and has been implicated as contributing to autoimmunity. 5 However, relatively little is known regarding signaling by this important cytokine.Like other ␥ c -dependent cytokines, 19 IL-21 activates the Janus family tyrosine kinases, Jak1 and Jak3. 2,20 Whereas IL-2, IL-7, IL-9, and IL-15 primarily activate Stat5a and Stat5b, and IL-4 primarily activates Stat6, IL-21 has been reported to activate Stat1, Stat3, and Stat5, with preferential activation of Stat1 and Stat3. 1,2,[20][21][22] Phosphorylation of tyrosine residues in the cytoplasmic domain of cytokine receptors can regulate downstream signaling pathways by providing docking sites for Src homology 2 (SH2) and/or phosphotyrosine binding (PTB) domain-containing proteins, 23,24 including STAT proteins. We now investigate the role of IL-21R tyrosines in mediating IL-21-induced STAT protein activation, and we also demonstrate the importance of these tyrosines as well as the MAPK and PI 3-kinase (PI3K)/Akt pathways in IL-21-mediated proliferation. Materials and methods MiceMice lacking IL-21R 4 and Stat1 25 have been described. Mice lacking Stat3 in T cells (T-cell Stat3) were generated by breeding Stat3 f/f mice 26 to transgenic mice expressing Cre recombinase under the control of CD4 regulatory elements. 27 Mice lacking Stat1 and T-cell Stat3 were generated by standard interbreeding. 28 Mice were analyzed at 6 to 16 weeks of age. Experiments were performed under protocols approved by Animal Use and Care Committees at NIH and the NYU School of Medicine, in accord with NIH guidelines. In vitro cell cultureSplenocytes were prepared by pressing spleens through fine nylon screens. Erythrocytes were deple...

IL-21 Stimulates Human Myeloma Cell Growth through an Autocrine IGF-1 Loop

“…IL-21 is thus distinct from IL-2, IL-7, and IL-15, which mainly activate STAT-5 (19). Although, the activation of STAT-1 by IL-21 was not previously detected by Brenne et al (8) in myeloma cells, we found it in the current study that is in agreement with numerous other studies on other cell types (12,20). Kinetics study indicates that Stat-1 activation is more transient than Stat-3 activation showing that STAT-3 might play a greater role in IL-21 induced clonogenicity.…”

“…This result is consistent with the notion that STAT-1 is a negative regulator of cell growth and survival (21) whereas Stat-3 is a positive regulator of survival and promotes oncogenesis (22). In addition to the JAK/STAT pathway, certain ␥c dependent cytokines can activate MAPK and PI3K/Akt pathways (20). In myeloma cells, we found that IL-21 triggers a rapid Erk 1/2 phosphorylation, a pathway known to contribute to proliferation.…”

The opposite effects of IL-15 and IL-21 on CLL B cells correlate with differential activation of the JAK/STAT and ERK1/2 pathways

“…A similar differential pattern of STAT molecule activation by IL-15 and IL-21 was observed in murine CD8 ϩ T cells. 43 However, an important difference between CD8 ϩ T cells and CLL cells is that IL-21 cooperates with IL-15 in inducing CD8 ϩ T-cell proliferation and function, 55 while IL-21 counteracts the antiapoptotic and proliferative effects of IL-15 in human CLL cells. The predominant activation of STAT3 by IL-21 may depend on the presence of an YXXQ STAT3 consensus binding motif 56 in the IL-21R intracytoplasmic domain, whereas STAT1 phosphorylation could be related to the activation of JAK1.…”

“…Our present findings only partially differ from the recent observation that IL-21 induces signaling via the Shc molecule in mouse CD8 ϩ T cells, albeit less efficiently than IL-15. 43 The different ability of IL-15 and IL-21 to activate ERK1/2 phosphorylation could explain both the antiapoptotic and the mitogenic activity of IL-15. Indeed, the MEK inhibitor UO126 blocked both the mitogenic and antiapoptotic activity of IL-15 on CLL cells.…”

“…39 Similar early signaling events are also activated by IL-21, IL-2, or IL-15 in normal lymphocytes. [41][42][43][44] In addition, IL-15 or IL-2, through the IL-2R␤, induces the recruitment of the adaptor protein Shc, 45,46 which regulates cell survival and proliferation via the Ras and the downstream MAPK p38 and/or MEK/ERK1/2 pathways. 47,48 IL-21R displays structural similarities with the IL-2R␤ 36 and weakly induces phosphorylation of Shc.…”