Intracellular mature IL-37 suppresses tumor metastasis via inhibiting Rac1 activation

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Abstract

IL-37, a newly found anti-inflammatory cytokine of the IL-1 family, has both extracellular and intracellular functions. Accumulating evidences indicate that it is also involved in tumor progression. However, the mechanism and its intracellular target are unclear. In this study, clinical data from 84 patients showed that loss or reduced expression of IL-37 in lung adenocarcinoma tissues was significantly associated with tumor metastasis. We further provided evidence that IL-37 inhibited effectively tumor metastasis in vitro and in vivo. Moreover, we uncovered a novel mechanism by which IL-37 suppressed tumor cell migration via its intracellular mature form (amino acids 46-218). Intracellular mature form of IL-37, but not its extracellular form, markedly inhibited migration of multiple kinds of tumor cells through inhibiting Rac1 activation. Mechanistically, intracellular mature IL-37 directly bound to the CAAX motif in the C-terminal hypervariable region of Rac1, and then inhibited Rac1 membrane translocation and subsequent downstream signaling. Our research identifies intracellular mature IL-37 as a novel endogenous inhibitor of Rac1. Given the crucial roles of Rac1 in tumor angiogenesis and metastasis, intracellular mature IL-37 might serve as a potential strategy for the control of Rac1 activity and tumor progression.

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Differential Localization of Rho Gtpases in Live Cells

David Michaelson, Joseph Silletti, Gretchen Murphy … (2001)

Determinants of membrane targeting of Rho proteins were investigated in live cells with green fluorescent fusion proteins expressed with or without Rho-guanine nucleotide dissociation inhibitor (GDI)α. The hypervariable region determined to which membrane compartment each protein was targeted. Targeting was regulated by binding to RhoGDIα in the case of RhoA, Rac1, Rac2, and Cdc42hs but not RhoB or TC10. Although RhoB localized to the plasma membrane (PM), Golgi, and motile peri-Golgi vesicles, TC10 localized to PMs and endosomes. Inhibition of palmitoylation mislocalized H-Ras, RhoB, and TC10 to the endoplasmic reticulum. Although overexpressed Cdc42hs and Rac2 were observed predominantly on endomembrane, Rac1 was predominantly at the PM. RhoA was cytosolic even when expressed at levels in vast excess of RhoGDIα. Oncogenic Dbl stimulated translocation of green fluorescent protein (GFP)-Rac1, GFP-Cdc42hs, and GFP-RhoA to lamellipodia. RhoGDI binding to GFP-Cdc42hs was not affected by substituting farnesylation for geranylgeranylation. A palmitoylation site inserted into RhoA blocked RhoGDIα binding. Mutations that render RhoA, Cdc42hs, or Rac1, either constitutively active or dominant negative abrogated binding to RhoGDIα and redirected expression to both PMs and internal membranes. Thus, despite the common essential feature of the CAAX (prenylation, AAX tripeptide proteolysis, and carboxyl methylation) motif, the subcellular localizations of Rho GTPases, like their functions, are diverse and dynamic.

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Interleukin 37 expression protects mice from colitis.

Leonard Collins, F Nieves, Eóin McNamee … (2011)

IL-37, a newly described member of the IL-1 family, functions as a fundamental inhibitor of innate inflammation and immunity. In the present study, we examined a role for IL-37 during experimental colitis. A transgenic mouse strain was generated to express human IL-37 (hIL-37tg), and these mice were subjected to dextran sulfate sodium (DSS)-induced colitis. Despite the presence of a CMV promoter to drive expression of IL-37, mRNA transcripts were not present in colons at the resting state. Expression was observed only upon disruption of the epithelial barrier, with a six- to sevenfold increase (P = 0.02) on days 3 and 5 after continuous exposure to DSS. During the development of colitis, clinical disease scores were reduced by 50% (P < 0.001), and histological indices of colitis were one-third less in hIL-37tg mice compared with WT counterparts (P < 0.001). Reduced inflammation was associated with decreased leukocyte recruitment into the colonic lamina propria. In addition, release of IL-1β and TNFα from ex vivo colonic explant tissue was decreased 5- and 13-fold, respectively, compared with WT (P ≤ 0.005), whereas IL-10 was increased sixfold (P < 0.001). However, IL-10 was not required for the anti-inflammatory effects of IL-37 because IL-10-receptor antibody blockade did not reverse IL-37-mediated protection. Mechanistically, IL-37 originating from hematopoietic cells was sufficient to exert anti-inflammatory effects because WT mice reconstituted with hIL-37tg bone marrow were protected from colitis. Thus, IL-37 emerges as key modulator of intestinal inflammation.

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Rac1 GTPase: a "Rac" of all trades.

E Bosco, J C Mulloy, Y. Zheng (2009)

Rac1, a member of the Rho family of GTPases, is an intracellular transducer known to regulate multiple signaling pathways that control cytoskeleton organization, transcription, and cell proliferation. Deregulated expression or activation patterns of Rac1 can result in aberrant cell signaling and numerous pathological conditions. Here, we highlight the physiological functions and signaling mechanisms of Rac1 and their relevance to disease.