The Osmoregulatory and the Amino Acid-regulated Responses of System A Are Mediated by Different Signal Transduction Pathways

The osmotic response of system A for neutral amino acid transport has been related to the adaptive response of this transport system to amino acid starvation. In a previous study (Ruiz-Montasell, B., M. Gómez-Angelats, F.J. Casado, A. Felipe, J.D. McGivan, and M. Pastor-Anglada. 1994. Proc. Natl. Acad. Sci. USA. 91:9569–9573), a model was proposed in which both responses were mediated by different mechanisms. The recent cloning of several isoforms of system A as well as the elucidation of a variety of signal transduction pathways involved in stress responses allow to test this model. SAT2 mRNA levels increased after amino acid deprivation but not after hyperosmotic shock. Inhibition of p38 activity or transfection with a dominant negative p38 did not alter the response to amino acid starvation but partially blocked the hypertonicity response. Inhibition of the ERK pathway resulted in full inhibition of the adaptive response of system A and no increase in SAT2 mRNA levels, without modifying the response to hyperosmolarity. Similar results were obtained after transfection with a dominant negative JNK1. The CDK2 inhibitor peptide-II decreased the osmotic response in a dose-dependent manner but did not have any effect on the adaptive response of system A. In summary, the previously proposed model of up-regulation of system A after hypertonic shock or after amino acid starvation by separate mechanisms is now confirmed and the two signal transduction pathways have been identified. The involvement of a CDK–cyclin complex in the osmotic response of system A links the activity of this transporter to the increase in cell volume previous to the entry in a new cell division cycle

Regulation of c-Jun NH2-terminal Kinase ( Jnk) Gene Expression during T Cell Activation

The c-Jun NH2-terminal kinases (JNKs) are a group of mitogen-activated protein (MAP) kinases that participate in signal transduction events mediating specific cellular functions. Activation of JNK is regulated by phosphorylation in response to cellular stress and inflammatory cytokines. Here, we demonstrate that JNK is regulated by a second, novel mechanism. Induction of Jnk gene expression is required in specific tissues before activation of this signaling pathway. The in vivo and in vitro ligation of the T cell receptor (TCR) leads to induction of JNK gene and protein expression. TCR signals are sufficient to induce JNK expression, whereas JNK phosphorylation also requires CD28-mediated costimulatory signals. Therefore, both expression and activation contribute to the regulation of the JNK pathway to ensure proper control during the course of an immune response

The JNK Pathway Regulates the In Vivo Deletion of Immature CD4+CD8+ Thymocytes

The extracellular signal-regulated kinase (ERK), the c-Jun NH2-terminal kinase (JNK), and p38 MAP kinase pathways are triggered upon ligation of the antigen-specific T cell receptor (TCR). During the development of T cells in the thymus, the ERK pathway is required for differentiation of CD4−CD8− into CD4+CD8+ double positive (DP) thymocytes, positive selection of DP cells, and their maturation into CD4+ cells. However, the ERK pathway is not required for negative selection. Here, we show that JNK is activated in DP thymocytes in vivo in response to signals that initiate negative selection. The activation of JNK in these cells appears to be mediated by the MAP kinase kinase MKK7 since high levels of MKK7 and low levels of Sek-1/MKK4 gene expression were detected in thymocytes. Using dominant negative JNK transgenic mice, we show that inhibition of the JNK pathway reduces the in vivo deletion of DP thymocytes. In addition, the increased resistance of DP thymocytes to cell death in these mice produces an accelerated reconstitution of normal thymic populations upon in vivo DP elimination. Together, these data indicate that the JNK pathway contributes to the deletion of DP thymocytes by apoptosis in response to TCR-derived and other thymic environment– mediated signals

JNK signalling in cancer: In need of new, smarter therapeutic targets

Copyright © 2013 The British Pharmacological Society. This is the accepted version of the following article: Bubici, C. and Papa, S. (2014), JNK signalling in cancer: in need of new, smarter therapeutic targets. British Journal of Pharmacology, 171: 24–37, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/bph.12432/abstract.The JNKs are master protein kinases that regulate many physiological processes, including inflammatory responses, morphogenesis, cell proliferation, differentiation, survival and death. It is increasingly apparent that persistent activation of JNKs is involved in cancer development and progression. Therefore, JNKs represent attractive targets for therapeutic intervention with small molecule kinase inhibitors. However, evidence supportive of a tumour suppressor role for the JNK proteins has also been documented. Recent studies showed that the two major JNK proteins, JNK1 and JNK2, have distinct or even opposing functions in different types of cancer. As such, close consideration of which JNK proteins are beneficial targets and, more importantly, what effect small molecule inhibitors of JNKs have on physiological processes, are essential. A number of ATP-competitive and ATP-non-competitive JNK inhibitors have been developed, but have several limitations such as a lack of specificity and cellular toxicity. In this review, we summarize the accumulating evidence supporting a role for the JNK proteins in the pathogenesis of different solid and haematological malignancies, and discuss many challenges and scientific opportunities in the targeting of JNKs in cancer.Kay Kendall Leukemia Fund, Italian Association for Cancer Research and Foundation for Liver Research

Enhancing chemosensitivity to gemcitabine via RNA interference targeting the catalytic subunits of protein kinase CK2 in human pancreatic cancer cells

<p>Abstract</p> <p>Background</p> <p>Pancreatic cancer is a complex genetic disorder that is characterized by rapid progression, invasiveness, resistance to treatment and high molecular heterogeneity. Various agents have been used in clinical trials showing only modest improvements with respect to gemcitabine-based chemotherapy, which continues to be the standard first-line treatment for this disease. However, owing to the overwhelming molecular alterations that have been reported in pancreatic cancer, there is increasing focus on targeting molecular pathways and networks, rather than individual genes or gene-products with a combination of novel chemotherapeutic agents.</p> <p>Methods</p> <p>Cells were transfected with small interfering RNAs (siRNAs) targeting the individual CK2 subunits. The CK2 protein expression levels were determined and the effect of its down-regulation on chemosensitization of pancreatic cancer cells was investigated.</p> <p>Results</p> <p>The present study examined the impact on cell death following depletion of the individual protein kinase CK2 catalytic subunits alone or in combination with gemcitabine and the molecular mechanisms by which this effect is achieved. Depletion of the CK2α or -α' subunits in combination with gemcitabine resulted in marked apoptotic and necrotic cell death in PANC-1 cells. We show that the mechanism of cell death is associated with deregulation of distinct survival signaling pathways. Cellular depletion of CK2α leads to phosphorylation and activation of MKK4/JNK while down-regulation of CK2α' exerts major effects on the PI3K/AKT pathway.</p> <p>Conclusions</p> <p>Results reported here show that the two catalytic subunits of CK2 contribute differently to enhance gemcitabine-induced cell death, the reduced level of CK2α' being the most effective and that simultaneous reduction in the expression of CK2 and other survival factors might be an effective therapeutic strategy for enhancing the sensitivity of human pancreatic cancer towards chemotherapeutic agents.</p

c-Jun N-terminal kinase phosphorylates DCP1a to control formation of P bodies

JNK-mediated phosphorylation of the mRNA-decapping protein DCP1a disrupts P body structure, mRNA stability, and gene expression in response to stress and inflammatory stimuli