The p42 and p44 mitogen-activated protein kinases (MAPKs), also called Erk2 and Erk1, respectively, have been implicated in proliferation as well as in differentiation programs. The specific role of the p44 MAPK isoform in the whole animal was evaluated by generation of p44 MAPK-deficient mice by homologous recombination in embryonic stem cells. The p44 MAPK ^–/– mice were viable, fertile, and of normal size. Thus, p44 MAPK is apparently dispensable and p42 MAPK (Erk2) may compensate for its loss. However, in p44 MAPK ^−/− mice, thymocyte maturation beyond the CD4 ⁺ CD8 ⁺ stage was reduced by half, with a similar diminution in the thymocyte subpopulation expressing high levels of T cell receptor (CD3 ^high ). In p44 MAPK ^−/− thymocytes, proliferation in response to activation with a monoclonal antibody to the T cell receptor in the presence of phorbol myristate acetate was severely reduced even though activation of p42 MAPK was more sustained in these cells. The p44 MAPK apparently has a specific role in thymocyte development.

The vascular endothelial growth factor A (VEGF-A) is essential during embryonic development as inactivation of only one allele of its gene results in embryonic lethality. Up-regulation of VEGF under physiological situations allows for adaptation to hypoxic stress, to transient inflammatory processes, and to wounding. Its expression also increases all along the process of neovascularization of solid and hematological tumors. The object of this article is to focus on the transcriptional regulation of its gene. The major cis-acting sequences and trans-activating factors will be described as well as the physiological and pathological situations leading to the intervention of such sequences and factors. We will also focus on two transcription factors essential to VEGF gene transcription: the hypoxia-inducible factor-1, which is responsible for its increased by hypoxia, as well as Sp1, which is implicated in the response to various extracellular stimuli.

Breast cancer is the most common type of cancer found in women and today represents a significant challenge to public health. With the latest breakthroughs in molecular biology and immunotherapy, very specific targeted therapies have been tailored to the specific pathophysiology of different types of breast cancers. These recent developments have contributed to a more efficient and specific treatment protocol in breast cancer patients. However, the main challenge to be further investigated still remains the emergence of therapeutic resistance mechanisms, which develop soon after the onset of therapy and need urgent attention and further elucidation. What are the recent emerging molecular resistance mechanisms in breast cancer targeted therapy and what are the best strategies to apply in order to circumvent this important obstacle? The main scope of this review is to provide a thorough update of recent developments in the field and discuss future prospects for preventing resistance mechanisms in the quest to increase overall survival of patients suffering from the disease.

Stability of the vascular endothelial growth factor (VEGF) mRNA is tightly regulated through its 3′-untranslated region (3′-UTR). Here, we demonstrate that VEGF mRNA levels are increased by anisomycin, a strong activator of stress-activated protein kinases. Hence, VEGF mRNA induction is inhibited by SB202190, an inhibitor of JNK and p38/HOG kinase. Furthermore, VEGF mRNA expression is increased in cells that overexpress JNK and p38/HOG by an increase in its stability. We show by two different approaches that anisomycin exerts its effect on the VEGF mRNA 3′-UTR. First, by using an in vitro mRNA degradation assay, the half-life of the VEGF mRNA 3′-UTR region transcript was found to be increased when incubated with extracts from anisomycin-treated cells; and second, the 3′-UTR was also sufficient to confer mRNA instability to theNhe3(Na⁺/H ⁺ exchanger 3) heterologous reporter gene, and anisomycin treatment stabilized the chimeric mRNA (Nhe3fused to the VEGF mRNA 3′-UTR). This chimeric mRNA is also more stable in cells overexpressing p38/HOG and JNK that have been stimulated by anisomycin. We show that such regulation is mediated through an AU-rich region of the 3′-UTR contained within a stable hairpin structure. By RNA electrophoretic mobility shift assays, we show that this region binds proteins specifically induced by anisomycin treatment. These findings clearly demonstrate a major role of stress-activated protein kinases in the post-transcriptional regulation of VEGF.

Metastatic renal cell carcinomas (mRCC) are highly vascularized tumors that are a paradigm for the treatment with antiangiogenesis drugs targeting the vascular endothelial growth factor (VEGF) pathway. The available drugs increase the time to progression but are not curative and the patients eventually relapse. In this study we have focused our attention on the molecular mechanisms leading to resistance to sunitinib, the first line treatment of mRCC. Because of the anarchic vascularization of tumors the core of mRCC tumors receives only suboptimal concentrations of the drug. To mimic this in vivo situation, which is encountered in a neoadjuvant setting, we exposed sunitinib-sensitive mRCC cells to concentrations of sunitinib below the concentration of the drug that gives 50% inhibition of cell proliferation (IC50). At these concentrations, sunitinib accumulated in lysosomes, which downregulated the activity of the lysosomal protease CTSB (cathepsin B) and led to incomplete autophagic flux. Amino acid deprivation initiates autophagy enhanced sunitinib resistance through the amplification of autolysosome formation. Sunitinib stimulated the expression of ABCB1 (ATP-binding cassette, sub-family B [MDR/TAP], member 1), which participates in the accumulation of the drug in autolysosomes and favor its cellular efflux. Inhibition of this transporter by elacridar or the permeabilization of lysosome membranes with Leu-Leu-O-methyl (LLOM) resensitized mRCC cells that were resistant to concentrations of sunitinib superior to the IC50. Proteasome inhibitors also induced the death of resistant cells suggesting that the ubiquitin-proteasome system compensates inhibition of autophagy to maintain a cellular homeostasis. Based on our results we propose a new therapeutic approach combining sunitinib with molecules that prevent lysosomal accumulation or inhibit the proteasome.

Age-related macular degeneration (AMD) was described for the first time in the 1840s and is currently the leading cause of blindness for patients over 65 years in Western Countries. This disease impacts the eye’s posterior segment and damages the macula, a retina section with high levels of photoreceptor cells and responsible for the central vision. Advanced AMD stages are divided into the atrophic (dry) form and the exudative (wet) form. Atrophic AMD consists in the progressive atrophy of the retinal pigment epithelium (RPE) and the outer retinal layers, while the exudative form results in the anarchic invasion by choroidal neo-vessels of RPE and the retina. This invasion is responsible for fluid accumulation in the intra/sub-retinal spaces and for a progressive dysfunction of the photoreceptor cells. To date, the few existing anti-AMD therapies may only delay or suspend its progression, without providing cure to patients. However, in the last decade, an outstanding number of research programs targeting its different aspects have been initiated by academics and industrials. This review aims to bring together the most recent advances and insights into the mechanisms underlying AMD pathogenicity and disease evolution, and to highlight the current hypotheses towards the development of new treatments, i.e., symptomatic vs. curative. The therapeutic options and drugs proposed to tackle these mechanisms are analyzed and critically compared. A particular emphasis has been given to the therapeutic agents currently tested in clinical trials, whose results have been carefully collected and discussed whenever possible.