Interleukin-22 Suppresses the Growth of A498 Renal Cell Carcinoma Cells via Regulation of STAT1 Pathway Fengbo Zhang*, Donghao Shang, Yuhai Zhang, Ye Tian Department of Urology Surgery, Beijing Friendship Hospital, Capital Medical University, Beijing, China Abstract Background: Renal cell carcinoma (RCC) is one of the most common kidney cancers and is highly resistant to chemotherapy. Accumulating evidence suggests that interleukin-22 (IL-22) may mediate host defense against varietal pathogens as a proinflammatory and anti-inflammatory cytokine. The purpose of this study is to assess the inhibitory effects of IL-22 on human RCC cell line A498 and to investigate the possible mechanisms underlying the anti-tumor effects of this cytokine. Methodology: A498 cells, a RCC cell line, were used to assess the inhibitory growth effects of IL-22 using the MTT assay and flow cytometric analysis in vitro. BALB/C nude mice bearing A498 cell xenografts were used to examine the antitumor efficacy of IL-22 in vivo. Western blotting assay was performed to detect the regulation of the intracellular signaling pathway of IL-22. Principal Findings: We found that IL-22 suppressed the growth of A498 cells in a dose-dependent manner and inhibited the growth of A498 xenografts. We also observed that IL-22 produced a dose-dependent inhibitory effect on A498 cells that involved the induction of G2/M cell cycle arrest without cell apoptosis. Moreover, we showed that the phosphorylation of STAT1 was increased and the phosphorylation of ERK1/2 was attenuated in A498 cells exposed to IL-22. The growth inhibition of A498 cells was partially revised after IL-22 treatment as the expression of STAT1 was knocked down. And inflammatory cytokines, interferon-a and tumor necrosis factor-a (TNF-a) were barely involved in the suppression of A498 cell xenografts treated with IL-22. Conclusions: IL-22 dose-dependently suppresses RCC cell line A498 cells in vitro and induces growth inhibition of A498 cell- bearing mouse xenografts. These results suggest that the anti-RCC effects of IL-22 are at least partially mediated through regulation of STAT1 signaling pathways and G2/M cell cycle arrest, rather than by inducing apoptosis and inflammatory cytokines. Citation: Zhang F, Shang D, Zhang Y, Tian Y (2011) Interleukin-22 Suppresses the Growth of A498 Renal Cell Carcinoma Cells via Regulation of STAT1 Pathway. PLoS ONE 6(5): e20382. doi:10.1371/journal.pone.0020382 Editor: Kevin D. Bunting, Emory University, United States of America Received October 15, 2010; Accepted May 2, 2011; Published May 23, 2011 Copyright: 2011 Zhang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: These authors have no support or funding to report. Competing Interests: The authors have declared that no competing interests exist. * E-mail: Fengbo_zhang@hotmail.com Introduction RCC is one of the most common malignant tumors arising in the kidney [1,2]; chemotherapeutic agents typically have little or no impact on this type of tumor [3–5]. In patients with RCC, there is poor survival following the development of metastatic disease; the 5-year survival rate for these patients is less than 20% [6,7]. Although immunotherapy with interleukin 2 (IL-2) and interferon- a (IFN-a) has been the standard treatment in patients with metastatic RCC, the response rate of patients with the disease to such treatment is only 10,20%, and the addition of the chemotherapeutic agent 5-FU does not notably increase the survival rate [8–10]. Therefore, there is currently an ongoing search for new and effective cytokine therapies for RCC. IL-22, discovered and reported by Dumoutier et al. in 2000, is a member of the IL-10 family of cytokines. IL-22 was identified as a T-cell-derived inducible factor produced by IL-9-activated murine T cells [11]. It has been found to represent an important effector molecule for activated Th1-, Th22-, Th17-, and Tc-cell subsets, natural killer (NK) and NKT cells [12–16]. In contrast to other cytokines, IL-22 does not mediate autocrine or paracrine functions between leukocytes, but instead serves as a mediator of communication between these cells. IL-22 may exert multiple effects on the immune system and may be involved in the acute phase response, activation of the innate immune system, induction of cell migration, inhibition of dentritic cell (DC) functions and attenuation of allergic responses [15–20]. Recent studies have shown that IL-22-producing T cells are more highly concentrated in lung TB granuloma than in blood and lymphoid tissues and that they contribute to anti-tuberculosis responses [12]. In addition, high systemic levels of IL-22, as well as of IL-10 and C-related Protein (CRP), in HIV-1C-infected Indian patients are associated with low viral replication in vitro [21]. IL-22 mediates its effects via a heterodimeric transmembrane receptor complex consisting of IL-22R and IL-10R2. It sequentially regulates several intracellular signal pathways including Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathways including STAT3, Jak1 and Tyk2 [22–25]. PLoS ONE | www.plosone.org 1 May 2011 | Volume 6 | Issue 5 | e20382