Javier Gómez

Dual role of Ras and Rho proteins: At the cutting edge of life and death

Small GTP‐binding proteins of the Ras superfamily are master controllers of the cell physiology. The range of processes in which these proteins are involved include cell cycle progression, cell division, regulation of cell morphology and motility and intracellular trafficking of molecules and organelles. The study of apoptosis, the physiological form of cell suicide, is progressively linking the functions of small G proteins to the control of the mechanisms that trigger the genetic programmes of cell death. To date, isoforms of the Ras and Rho groups have been related to both promotion and suppression of apoptosis. Further, signalling pathways driven by these proteins have been associated with the function and/or expression of molecules that regulate apoptotic responses. Thus, all available evidence points to a critical role for Ras and Rho proteins as major gatekeepers of the decision between cellular life and death.

The Bcl-2 gene is differentially regulated by IL-2 and IL-4: role of the transcription factor NF-AT.

The murine TS1αβ T cell line expresses the anti-apoptotic protein Bcl-2 upon IL-2 stimulation, whereas IL-4-mediated growth of this cell line proceeds in the absence of Bcl-2 expression. In addition, IL-4 stimulation inhibits Bcl-2 expression and modulates its mRNA level. IL-2-induced DNA binding activity for these transcription factors is sensitive to phosphatidylinositol 3 kinase inhibitor wortmannin and to Rho inhibitor Clostridium difficile toxin B, which inhibit IL-2-induced Bcl-2 expression. NF-AT transcription factor appears to be the most important in the control Bcl-2 expression, since inhibition of the calcium-calmodulin-dependent phosphatase calcineurin, which regulates NF-AT activity, downregulates Bcl-2 expression in IL-2-stimulated cells. Constitutive expression of this phosphatase also upregulates Bcl-2 expression in IL-4-stimulated cells. In addition, a dominant negative NF-AT expression vector downregulates Bcl-2 expression in IL-2-stimulated cells. These results suggest that IL-2 induction of Bcl-2 expression may be directly or indirectly mediated by NF-AT.

IL-2 deprivation triggers apoptosis which is mediated by c-Jun N-terminal kinase 1 activation and prevented by Bcl-2

A variety of environmental stresses, as well as inflammatory cytokines, induce activation of c-Jun N-terminal kinases. We describe here that IL-2 deprivation-induced apoptosis in TS1αβ cells does not modify c-Jun protein levels and correlates Bcl-2 downregulation and an increase in JNK1, but not JNK2, activity directly related to the induction of apoptosis. Indeed, downregulation of JNK1 expression using antisense oligonucleotides inhibits apoptosis induced by IL-2 withdrawal. Overexpression of Bcl-2 promotes cell survival and blocks JNK1 activation as well as apoptosis caused by IL-2 deprivation. This suggests that inhibition of the JNK1 signaling pathway may be a mechanism through which Bcl-2 promotes cell survival and prevents apoptosis triggered by growth factor withdrawal.

Towards a solvent acidity scale: the calorimetry of the N-methyl imidazole probe

This paper reports a rather straightforward calorimetric method for the precise determination of the acidity of organic solvents. From the calculated enthalpies of solvation (ΔHsolv) of the probe compounds N-methylimidazole and N-methylpyrrole and the known relative permittivity (Iµ) of the solvent ΔHacid is obtained through the equation: ΔHacid=–[ΔH0solv(N-methylimidazole)-ΔH0solv(N-methylpyrrole)]+ 18.760 f(Iµ)+ 1.69. The proposed method allowed us to determine the acidity of 36 solvents, including some slightly acidic ones, whose acidity is difficult to obtain by existing methods.

CALORIMETRIC QUANTIFICATION OF THE HYDROGEN-BOND ACIDITY OF SOLVENTS AND ITS RELATIONSHIP WITH SOLVENT POLARITY

A new solvent polarity–polarizability scale (SPP) has been used to reevaluate the hydrogen-bond acidity scale of organic solvents previously reported and has been extended to a new set of solvents. The hydrogen-bond acidity, expressed as the enthalpy term ΔacidH, has been evaluated by measuring the differences between the solvation enthalpies of N-methylimidazole and N-methylpyrrole in these solvents along with the solvent polarity–polarizability (SPP) values. The ΔacidH values for 63 solvents are reported.

Role of NF-kappaB in the control of apoptotic and proliferative responses in IL-2-responsive T cells

The NF-kappaB/Rel/IkappaB family of transcription factors regulates a number of genes involved in a wide variety of biological processes. The activation of p53, c-myc and Ras genes suggests a role for NF-kappaB in cell proliferation; NF-kappaB is also important in immune and inflammatory responses. By virtue of its role in apoptosis, NF-kappaB participates in the thymus as well as in embryonic development. The NF-kappaB family of transcription factors is also involved in viral transcription, transformation and in the development of some types of human cancers. Given the pivotal role of NF-kappaB, clarification is needed of the mechanisms through which its deregulation contributes to disease. Several aspects of NF-kappaB regulation, such as phosphatase involvement, the mechanism of IkappaB ubiquitination and the regulation of nuclear translocation, remain obscure. Here, we review and discuss the function of NF-kappaB activation in IL-2-stimulation and in apoptosis induced by IL-2 deprivation in T cells.

Ras-mediated cell proliferation and cell death: some clues from the interleukin-2 receptor system

Oncoproteins of the Ras family have been extensively studied because of their implication in human cancer. Their roles have been primarily assigned to the commandment of cell proliferation and suppression of apoptosis, which has also been demonstrated by the involvement of Ras activation in the signal transduction pathways triggered by most cytokine receptors. Nevertheless, the functions of Ras proteins have been extended in the last years by the findings showing that they can also act as promoters or enhancers of apoptosis in various systems and conditions. These considerations have raised the issue as to how the signals delivered by Ras are regulated and translated in terms of cellular responses, suggesting that signal complementation may direct the final fate of cells. As an example, the interleukin-2 receptor system may represent a useful model in which the meaning of Ras signals may be evaluated in terms of interactions with other simultaneous signalling events, since knowledge of the biochemical events triggered by the interaction of interleukin-2 with its cell surface receptor in lymphocytes has allowed the proposal of a complete signalling model arranged in three independent channels, one of which is mediated by Ras.