The role of Ras in T lymphocyte activation

Differential contribution for ERK1 and ERK2 kinases in BRAFV600E-triggered phenotypes in adult mouse models

The BRAF gene is mutated in a plethora of human cancers. The majority of such molecular lesions result in the expression of a constitutively active BRAF variant (BRAFV600E) which continuously bolsters cell proliferation. Although we recently addressed the early effects triggered by BRAFV600E-activation, the specific contribution of ERK1 and ERK2 in BRAFV600E-driven responses in vivo has never been explored. Here we describe the first murine model suitable for genetically dissecting the ERK1/ERK2 impact in multiple phenotypes induced by ubiquitous BRAFV600E-expression. We unveil that ERK1 is dispensable for BRAFV600E-dependent lifespan shortening and for BRAFV600E-driven tumor growth. We show that BRAFV600E-expression provokes an ERK1-independent lymphocyte depletion which does not rely on p21CIP1-induced cell cycle arrest and is unresponsive to ERK-chemical inhibition. Moreover, we also reveal that ERK1 is dispensable for BRAFV600E-triggered cytotoxicity in lungs and that ERK-chemical inhibition abrogates some of these detrimental effects, such as DNA damage, in Club cells but not in pulmonary lymphocytes. Our data suggest that ERK1/ERK2 contribution to BRAFV600E-driven phenotypes is dynamic and varies dependently on cell type, the biological function, and the level of ERK-pathway activation. Our findings also provide useful insights into the comprehension of BRAFV600E-driven malignancies pathophysiology as well as the consequences in vivo of novel ERK pathway-targeted anti-cancer therapies.

Involvement of H-Ras in the adaptive immunity of Nile tilapia by regulating lymphocyte activation

H-Ras is a guanosine triphosphatase (GTPase), which acts as a molecular switch and controls multiple important cellular processes including lymphocyte activation and function. However, regulatory mechanism of adaptive immune response by H-Ras remains unclear in non-mammalian animals. In the present study, we investigated the involvement of H-Ras in lymphocyte activation with a teleost model Oreochromis niloticus. H-Ras from O. niloticus (On-H-Ras) is highly conserved with those from other vertebrates. The mRNA of On-H-Ras showed a wide expression pattern in the lymphoid-tissues and with the highest level in liver. After Aeromonas hydrophila infection, transcription of On-H-Ras was significantly induced on day 8 but came back to basal level on day 16, suggesting that On-H-Ras potentially participated in primary response during the adaptive immunity. Furthermore, On-H-Ras mRNA was obviously up-regulated when leukocytes were activated by T lymphocyte mitogen PHA in vitro. Meanwhile, protein level of H-Ras was also augmented once leukocytes were stimulated with lymphocyte receptor signaling agonist PMA and ionomycin. More importantly, once Ras activity was inhibited by specific inhibitor, the up-regulation of lymphocyte activation marker CD122 was obviously impaired during lymphocyte activation process. Therefore, On-H-Ras regulated lymphocyte activation through both mRNA and protein level. Altogether, our results illustrated the involvement of H-Ras in teleost adaptive immunity via controlling lymphocyte activation, and thus provided a novel perspective to understand evolution of the lymphocyte-mediated adaptive immunity.

Synthetic Lethality Induced by Loss of PKC δ and Mutated Ras

Synthetic lethal interaction between oncogenic Ha-ras and loss of PKC has been demonstrated. Recently, the authors reported that the concurrent knockdown of PKC α and β, via upregulating PKC δ, sensitizes cells with aberrant Ras signaling to apoptosis. As a continuation of the study, using shRNA, the authors demonstrate that loss of PKC δ causes a lethal reaction in NIH3T3/Hras or prostate cancer DU145 cells that overexpress JNK. In this apoptotic process, PKC α and β are upregulated and then associated with RACK1 (an adaptor for activated PKC) and JNK. Immunoblotting analysis shows that JNK is phosphorylated, accompanied with caspase 8 cleavage. The inhibition of JNK abrogates this apoptotic process triggered by PKC δ knockdown. Interestingly, without blocking PKC δ, the concurrent overexpression of wt- or CAT-PKC α and β is insufficient to induce apoptosis in the cells. Together with the authors' previous findings, the data suggest that PKC α/β and δ function oppositely to maintain a balance that supports cells expressing v-ras to survive and prevents them from being eliminated through oncogenic stress-induced apoptosis.

Nore1B regulates TCR signaling via Ras and Carma1

Nore1A was originally identified as a potential Ras effector, and Nore1B is an alternatively spliced isoform. Both share a Ras/Rap association domain (RA domain) but only Nore1A contains sequence motifs that predict SH3 domain binding and diacylglycerol/phorbol ester binding in the amino-terminal region. Here we report that Carma1 binds to Nore1A and Nore1B through the RA domain and that Carma1 interacts with active Ras in the presence of Nore1B. RNA interference against Nore1B attenuates NF-kappaB activation induced by T cell receptor (TCR) ligation, but not NF-kappaB activation induced by TNFalpha or lipoteichoic acid. In addition, Nore1B is also required for KiRas GV12-mediated ERK1 activation and Elk1 reporter activity in T cells. We also provide evidence that knockdown of Nore1B also impairs polarized redistribution of Ras at the B cell-T cell immune interface. Together, these findings suggest that endogenous Nore1B recruits active Ras to the APC-T cell interface and mediates the interaction between Ras and Carma1.

Role of mitochondria in the immune response to cancer: a central role for Ca2+

This study demonstrates that Ca2+ stimulates mitochondrial energy metabolism during spleen lymphocyte activation in response to the ascitic Walker 256 tumor in rats. Intracellular Ca2+ concentrations, phosphorylated protein kinase C (pPKC) levels, Bcl-2 protein contents, interleukin-2 (IL-2) levels, mitochondrial uncoupling protein-2 (UCP-2) contents and reactive oxygen species (ROS) were significantly elevated in these activated lymphocytes. Mitochondria of activated lymphocytes exhibited high free Ca2+ concentrations in the matrix and enhanced oligomycin-sensitive oxygen consumption, indicating an increased rate of oxidative phosphorylation. The production of ROS was largely decreased by diphenylene iodinium in the activated lymphocytes, suggesting that NADPH oxidase is the prevalent source of these species. Accumulation of UCP-2 and the anti-apoptotic protein Bcl-2 is probably important to prevent mitochondrial dysfunction and cell death elicited by the sustained high levels of intracellular Ca2+ and ROS and may explain the observed higher resistance from activated lymphocytes against the opening of the mitochondrial membrane permeability pore (MPT). All these changes were blocked by pretreatment of the rats with verapamil, an L-type Ca2+ channel antagonist. These data demonstrate a central role of Ca2+ in the control of mitochondrial bioenergetics in spleen lymphocytes during the immune response to cancer.

Differential effect of calcineurin inhibitors, anti-CD25 antibodies and rapamycin on the induction of FOXP3 in human T cells

BACKGROUND

The transcription factor FOXP3 has been identified as the molecule associated with the regulatory function of CD25+ T cells.

METHODS

To understand the biology of FOXP3+ T cells in allogeneic reactions, we measured FOXP3 mRNA expression levels in allostimulated CD25 cells and CD25 cells and in peripheral blood mononuclear cells (PBMC). The effect of immunosuppressive drugs on FOXP3 expression was studied in mixed lymphocyte reactions (MLR) in the presence and absence of calcineurin inhibitors (CNI), alphaCD25 mAb, and Rapamycin (Rapa), and analyzed in biopsies from cardiac allograft recipients during acute rejection by quantitative (Q)-PCR.

RESULTS

FOXP3 mRNA expression was restricted to the CD25 population that inhibited the proliferation of allostimulated CD25 cells. In the MLR FOXP3 was readily induced after allostimulation. Kinetic examination of the MLR showed a 10-20-fold higher FOXP3 mRNA expression level after 5 days of culture. The CNI Cyclosporin and Tacrolimus, and alphaCD25 mAb inhibited in vitro induced FOXP3 gene transcription (range 70%-90%), whereas Rapa did not inhibit the induction. After clinical heart transplantation the highest FOXP3 mRNA expression levels were measured in biopsies during acute rejection (P=0.03).

CONCLUSIONS

The high FOXP3 mRNA levels during allogeneic responses in vivo and in vitro suggests that regulatory activities of CD25 T cells or the generation of these cells is an intrinsic part of activation. CNI and alphaCD25 mAb in contrast to Rapa, did interfere with this immunosuppressive counter-mechanism and as a result might have an inhibitory effect to tolerance induction after transplantation.