In this study, we demonstrate that the E3 ubiquitin ligase gene related to anergy in lymphocytes (GRAIL) is expressed in quiescent naive mouse and human CD4 T cells and has a functional role in inhibiting naive T cell proliferation. Following TCR engagement, CD28 costimulation results in the expression of IL-2 whose signaling through its receptor activates the Akt-mammalian target of rapamycin (mTOR) pathway. Activation of mTOR allows selective mRNA translation, including the epistatic regulator of GRAIL, Otubain-1 (Otub1), whose expression results in the degradation of GRAIL and allows T cell proliferation. The activation of mTOR appears to be the critical component of IL-2R signaling regulating GRAIL expression. CTLA4-Ig treatment blocks CD28 costimulation and resultant IL-2 expression, whereas rapamycin and anti-IL-2 treatment block mTOR activation downstream of IL-2R signaling. Thus, all three of these biotherapeutics inhibit mTOR-dependent translation of mRNA transcripts, resulting in blockade of Otub1 expression, maintenance of GRAIL, and inhibition of CD4 T cell proliferation. These observations provide a mechanistic pathway sequentially linking CD28 costimulation, IL-2R signaling, and mTOR activation as important requirements for naive CD4 T cell proliferation through the regulation of Otub1 and GRAIL expression. Our findings also extend the role of GRAIL beyond anergy induction and maintenance, suggesting that endogenous GRAIL regulates general cell cycle and proliferation of primary naive CD4 T cells.
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"Previously, OTUB1 has been implicated in the regulation of several physiological and pathological processes independently of its de-ubiquitinase activity. OTUB1 has been reported to regulate T-cell anergy by enhancing the degradation of the E3 ligase GRAIL (gene related to anergy in lymphocytes) (Lin et al, 2009), to augment TGF-b signaling by inhibiting degradation of phosphorylated SMAD2/3 (Herhaus et al, 2013), and to suppress DNA-damage-dependent chromatin ubiquitination (Nakada et al, 2010) and MDM2-mediated ubiquitination of the tumor suppressor p53 (Sun et al, 2012). Here we found that OTUB1 promotes tumorigenic transformation of wt RAS cells by triggering the RAS/ MAPK pathway. "
[Show abstract][Hide abstract]ABSTRACT: Activation of the RAS oncogenic pathway, frequently ensuing from mutations in RAS genes, is a common event in human cancer. Recent reports demonstrate that reversible ubiquitination of RAS GTPases dramatically affects their activity, suggesting that enzymes involved in regulating RAS ubiquitination may contribute to malignant transformation. Here, we identified the de‐ubiquitinase OTUB1 as a negative regulator of RAS mono‐ and di‐ubiquitination. OTUB1 inhibits RAS ubiquitination independently of its catalytic activity resulting in sequestration of RAS on the plasma membrane. OTUB1 promotes RAS activation and tumorigenesis in wild‐type RAS cells. An increase of OTUB1 expression is commonly observed in non‐small‐cell lung carcinomas harboring wild‐type KRAS and is associated with increased levels of ERK1/2 phosphorylation, high Ki67 score, and poorer patient survival. Our results strongly indicate that dysregulation of RAS ubiquitination represents an alternative mechanism of RAS activation during lung cancer development.
Full-text · Article · Feb 2016 · EMBO Molecular Medicine
"GRAIL may mediate anergy induction by down-regulating the expression of CD3, CD40L, CD151, and CD81, as well as affecting rearrangement of the actin cytoskeleton (Whiting et al., 2011). Moreover, Lin et al. (2009) suggested that GRAIL expressed in quiescent naïve CD4 T cells has a functional role in inhibiting cell proliferation, and its degradation is required to allow T cell proliferation. Mehlhop-Williams and Bevan (2014) recently showed that memory CD8 + T cells exhibit reduced sensitivity to activation through TCR. "
[Show abstract][Hide abstract]ABSTRACT: Memory T cells resist co-stimulatory blockade and present a unique therapeutic challenge in transplantation and autoimmune diseases. Herein, we determined whether memory T cells express less "tolerogenic" genes than naïve T cells to reinforce a proliferative response under the deprivation of co-stimulatory signals. The expression of ∼40 tolerogenic genes in memory and naïve CD4(+) T cells was thus assessed during an in vitro TCR stimulation without co-stimulation. Briefly, upon TCR stimulation with an anti-CD3 mAb alone, memory CD4(+) T cells exhibited more proliferation than naïve CD4(+) T cells. To our surprise, at 24h upon anti-CD3 mAb stimulation, memory CD4(+) T cells expressed more than a 5-fold higher level of the transcription factor Egr2 and a 20-fold higher level of the transmembrane E3 ubiquitin ligase GRAIL than those in naïve T cells. Hence, the high-level expression of tolerogenic genes, Egr2 and GRAIL, in memory CD4(+) T cells does not prevent cell proliferation. Importantly, anti-CD3 mAb-stimulated memory CD4(+) T cells expressed high protein/gene levels of phosphorylated STAT5, Nedd4, Bcl-2, and Bcl-XL. Therefore, co-stimulation-independent proliferation of memory CD4(+) T cells may be due to elevated expression of molecules that support cell proliferation and survival, but not lack of tolerogenic molecules.
Full-text · Article · Oct 2014 · Molecular Immunology
"In naïve CD4 T cells, engagement of the IL-2R induced phosphorylation of STAT5 and Akt. Phosphorylation of Akt leads to mTOR activation and resultant S6K1 phosphorylation, in turn downregulating the cell cycle inhibitor Kip1/p27 [11, 19] and the T cell unresponsiveness factor GRAIL . When IL-2R signaling was abrogated by anti-IL-2 antibody there was a lack of STAT5, Akt, and S6K1 phopshorylation while Kip1/p27 and GRAIL expression were maintained. "
[Show abstract][Hide abstract]ABSTRACT: The signaling pathways utilized by naïve and experienced effector CD4 T cells during activation and proliferation were evaluated. While inhibition of either mTOR or MAPK alone was able to inhibit naïve T cell proliferation, both mTOR and MAPK (ERK) pathway inhibition was required to efficiently block experienced, effector CD4 T cell proliferation. This was demonstrated both in vitro, and in vivo by treating mice with collagen-induced arthritis using mTOR and/or ERK inhibitors. The combination of mTOR and ERK inhibition prevented or treated disease more efficiently than either agent alone. These data illustrate the different requirements of naïve and experienced effector CD4 T cells in the use of the mTOR and MAPK pathways in proliferation, and suggest that therapies targeting both the mTOR and MAPK pathways may be more effective than targeting either pathway alone in the treatment of CD4 T cell-mediated autoimmunity.
Full-text · Article · Oct 2011 · Clinical Immunology