Epithelial-to-Mesenchymal Transition Chain , α to the Soluble Interleukin-15 Receptor Membrane-Bound Interleukin-15 that Induces , in Response Human Renal Cancer Cells Express a Novel

Although interleukin-15 (IL-15) is a powerful immunomodulatory factor that has been proposed for cancer immunotherapy, its intratumoral expression may be correlated with tumor progression and/or poor clinical outcome. Therefore, neoplasias potentially sensitive to immunotherapy should be checked for their IL-15 expression and function before choosing immunotherapy protocols. Primary human renal cancer cells (RCC) express a novel form of membranebound IL-15 (mb-IL-15), which displays three major original properties: (a) It is expressed as a functional membrane homodimer of 27 kDa, (b) it is shed in the extracellular environment by the metalloproteases ADAM17 and ADAM10, and (c) its stimulation by soluble IL-15 receptor A (s-IL-15RA) chain triggers a complex reverse signal (mitogen-activated protein kinases, FAK, pMLC) necessary and sufficient to ~induce epithelial-mesenchymal transdifferentiation (EMT), a crucial process in tumor progression whose induction is unprecedented for IL-15. In these cells, complete EMT is characterized by a dynamic reorganization of the cytoskeleton with the subsequent generation of a mesenchymal/contractile phenotype (A-SMA and vimentin networks) and the loss of the epithelial markers E-cadherin and ZO-1. The retrosignaling functions are, however, hindered through an unprecedented cytokine/receptor interaction of mb-IL-15 with membraneassociated IL-15RA subunit that tunes its signaling potential competing with low concentrations of the s-IL-15RA chain. Thus, human RCC express an IL-15/IL-15R system, which displays unique biochemical and functional properties that seem to be directly involved in renal tumoral progression. [Cancer Res 2009;69(4):1561–9] Introduction Interleukin-15 (IL-15) is a proinflammatory cytokine that plays an important role in both the innate and adaptive immune system. IL-15 promotes the activation of neutrophils and macrophages and is critical to dendritic cell function. In addition, IL-15 is essential to the development, homeostasis, function, and survival of natural killer (NK) cells, NK T cells, and memory CD8+ T cells. Based on these properties, IL-15 has been proposed as a useful cytokine for immunotherapy (1). Indeed, in preclinical models, IL-15 displays antitumor activity mainly mediated by CD8+ T cells and NK cells (2–4). However, in humans, recent clinical studies reported a correlation between high intratumoral IL-15 concentrations and poor clinical outcome in patients with lung or head and neck cancers (5, 6). Moreover, IL-15 production by human melanoma, colon cancer, or prostate cancer cells contributes to the progression of the disease (7–12). IL-15 is a 14-kDa cytokine that belongs to the four-helix bundle cytokine family and was first characterized by its ability to substitute IL-2. Indeed, IL-15 shares with IL-2 the IL-2 receptor (IL-2R) h and g chains but has a unique private a chain (IL-15Ra) that is responsible for high-affinity binding and signal transduction (13). In addition, IL-15Ra may be secreted as a functional soluble molecule (s-IL-15Ra) that behaves as an agonist or antagonist for IL-15, depending on its cleavage mechanism certainly in mouse and probably in human (14–16). Three different functional forms of IL-15 have been identified: (a) the soluble cytokine secreted by accessory cells (at pg/mL) that activates cells expressing high-affinity IL-15R (1), (b) the hyper IL15 (s-IL-15/IL-15Ra complex) 100-fold more efficient than the noncomplexed soluble cytokine (17, 18), and (c) the membranebound forms (mb-IL-15) considered as the dominant physiologic forms of the cytokine (17, 19, 20). Thus, a mb-IL-15 anchored through IL-15Ra, which activates by transpresentation of bystander cells, has been described. This mechanism is essential for lymphoid homeostasis, both in mice and man. In addition, human cells display two other forms of mb-IL-15. The first one, anchored at the surface of spleen stromal cells through the IL-15Rahgc complex, is able to induce NK differentiation (17). The other one is an IL-15R–independent mb-IL-15 that can function as a receptor and participate in reverse signaling and/or act in a juxtacrine fashion (19). IL-15 has been involved in renal inflammatory pathologies in mice and human but with contrasting conclusion between the two species (21, 22). Furthermore, cytosolic and nonsecreted IL-15 Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). K. Khawam, J. Giron-Michel, and Y. Gu contributed equally to this article. Present address for Y. Gu: Department of Clinical Oncology, Nanjing Medical University, China. Requests for reprints: Azzarone Bruno, Institut National de la Sante et de la Recherche Medicale, UMR 542, Bâtiment Lavoisier, Hôpital Paul Brousse, 14, Avenue Paul Vaillant Couturier, 94807, Villejuif Cedex, France. Phone: 33-0145595343; Fax: 330145595344; E-mail: bazzarone@hotmail.com. I2009 American Association for Cancer Research. doi:10.1158/0008-5472.CAN-08-3198 www.aacrjournals. org 1561 Cancer Res 2009; 69: (4). February 15, 2009 Research Article Research. on July 10, 2014. © 2009 American Association for Cancer cancerres.aacrjournals. org Downloaded from Published OnlineFirst February 3, 2009; DOI: 10.1158/0008-5472.CAN-08-3198