Lipid metabolic reprogramming in cancer cells.

Many human diseases, including metabolic, immune and central nervous system disorders, as well as cancer, are the consequence of an alteration in lipid metabolic enzymes and their pathways. This illustrates the fundamental role played by lipids in maintaining membrane homeostasis and normal function in healthy cells. We reviewed the major lipid dysfunctions occurring during tumor development, as determined using systems biology approaches. In it, we provide detailed insight into the essential roles exerted by specific lipids in mediating intracellular oncogenic signaling, endoplasmic reticulum stress and bidirectional crosstalk between cells of the tumor microenvironment and cancer cells. Finally, we summarize the advances in ongoing research aimed at exploiting the dependency of cancer cells on lipids to abolish tumor progression.

TAp73 loss favors Smad-independent TGF-ß signaling that drives EMT in pancreatic ductal adenocarcinoma.

Advances made in pancreatic cancer therapy have been far from sufficient and have allowed only a slight improvement in global survival of patients with pancreatic ductal adenocarcinoma (PDA). Recent progresses in chemotherapy have offered some hope for an otherwise gloomy outlook, however, only a limited number of patients are eligible because of important cytotoxicity. In this context, enhancing our knowledge on PDA initiation and evolution is crucial to highlight certain weaknesses on which to specifically target therapy. We found that loss of transcriptionally active p73 (TAp73), a p53 family member, impacted PDA development. In two relevant and specific engineered pancreatic cancer mouse models, we observed that TAp73 deficiency reduced survival and enhanced epithelial-to-mesenchymal transition (EMT). Through proteomic analysis of conditioned media from TAp73 wild-type (WT) and deficient pancreatic tumor cells, we identified a secreted protein, biglycan (BGN), which is necessary and sufficient to mediate this pro-EMT effect. Interestingly, BGN is modulated by and modulates the transforming growth factor-ß (TGF-ß) pathway, a key regulator of the EMT process. We further examined this link and revealed that TAp73 impacts the TGF-ß pathway by direct regulation of BGN expression and Sma and Mad-related proteins (SMADs) expression/activity. Absence of TAp73 leads to activation of TGF-ß signaling through a SMAD-independent pathway, favoring oncogenic TGF-ß effects and EMT. Altogether, our data highlight the implication of TAp73 in the aggressiveness of pancreatic carcinogenesis through modulation of the TGF-ß signaling. By suggesting TAp73 as a predictive marker for response to TGF-ß inhibitors, our study could improve the classification of PDA patients with a view to offering combined therapy involving TGF-ß inhibitors.

Stromal SLIT2 impacts on pancreatic cancer-associated neural remodeling.

Pancreatic ductal adenocarcinoma (PDA) is a critical health issue in the field of cancer, with few therapeutic options. Evidence supports an implication of the intratumoral microenvironment (stroma) on PDA progression. However, its contribution to the role of neuroplastic changes within the pathophysiology and clinical course of PDA, through tumor recurrence and neuropathic pain, remains unknown, neglecting a putative, therapeutic window. Here, we report that the intratumoral microenvironment is a mediator of PDA-associated neural remodeling (PANR), and we highlight factors such as 'SLIT2' (an axon guidance molecule), which is expressed by cancer-associated fibroblasts (CAFs), that impact on neuroplastic changes in human PDA. We showed that 'CAF-secreted SLIT2' increases neurite outgrowth from dorsal root ganglia neurons as well as from Schwann cell migration/proliferation by modulating N-cadherin/ß-catenin signaling. Importantly, SLIT2/ROBO signaling inhibition disrupts this stromal/neural connection. Finally, we revealed that SLIT2 expression and CAFs are correlated with neural remodeling within human and mouse PDA. All together, our data demonstrate the implication of CAFs, through the secretion of axon guidance molecule, in PANR. Furthermore, it provides rationale to investigate the disruption of the stromal/neural compartment connection with SLIT2/ROBO inhibitors for the treatment of pancreatic cancer recurrence and pain.

Long-term variations of AP-1 composition after CRH stimulation: consequence on POMC gene regulation.

It has been shown previously that the CRH-induced POMC gene transcription in the corticotroph cell line AtT-20 involves an increase in AP-1 DNA binding activity that remained elevated for at least 24 h, while induction of c-fos was transient. We showed here that there were dramatic changes in protein components of AP-1 including an initial recruitment of the transcriptional activators c-Fos and Jun-B then of Fra-2 and Jun-D. Changes in AP-1 composition were concomitant with a decrease in POMC mRNA. Moreover, the presence of Fra-2/Jun-D dimers suppressed the CRH-induction of c-fos mRNA expression as well as c-Fos/Jun-B recruitment in AP-1 complexes, suggesting the existence of autoregulatory loops of AP-1 composition that involve complex interactions between the different members of the Jun and Fos families. It is concluded that CRH stimulation of corticotroph cells involves successive recruitment of activators and repressors, possibly contributing to prevent over expression of POMC.

Is light-regulated AP-1 binding in the rat suprachiasmatic nucleus gated by the circadian clock?

In mammals, photic entrainment of circadian rhythms likely involves light- and clock-dependent expression of immediate early genes, including fos-like and jun-like genes, in the rat suprachiasmatic nucleus. Using an electrophoretic mobility shift assay, we evaluated whether the photic regulation of DNA-binding activity and composition of activating protein-1 (AP-1) complexes in the suprachiasmatic nucleus is also dependent on circadian phase. Phase-dependent light inducibility in the expression of fra-2 and c-fos genes and in immunoreactive Fra-2 and c-Fos protein expression was also evaluated, by in situ hybridization and immunocytochemistry. Light's effects on AP-1 DNA-binding differed both qualitatively and quantitatively according to the circadian phase at which light was applied. This phase dependence accounted for by both compartmentalization of proteins involved in constitutive AP-1 complexes within the nucleus or cytoplasm and control of the extent to which the expression of specific complexes was induced. It was then shown that the mechanisms by which the circadian clock gates the photic induction of AP-1 components differed according to the nature of the protein.

DNA microarray analysis and functional profile of pituitary transcriptome under core-clock protein BMAL1 control.

Although it is known to contain five cell types that synthesize and release hormones with a circadian pattern, the pituitary gland is poorly characterized as a circadian oscillator. By a differential microarray analysis, 252 genes were found to be differentially expressed in pituitaries from Bmal1(-/-) knockout versus wild-type mice. By integrative analyses of the data set with the Annotation, Visualization, and Integrated Discovery (DAVID) Bioinformatics Resources annotation analysis system, pituitary genes with altered expression in Bmal1(-/-) mice were dispatched among functional categories. Clusters of genes related to signaling and rhythmic processes as well as transcription regulators, in general, were found enriched in the data set, as were pathways such as circadian rhythm, transforming growth factor ß (TGFß) signaling, valine, leucine, and isoleucine degradation, and peroxisome proliferator-activated receptor (PPAR) signaling pathways. Gene Ontology term overrepresentation analyses revealed significant enrichment for genes involved in 10 key biological processes. To determine whether genes with altered expression in Bmal1(-/-) mice were actually circadian genes, we further characterized in the mouse pituitary gland the daily pattern of some of these genes, including core-clock genes. Core-clock genes and genes selected from three identified overrepresented biological processes, namely, hormone metabolic process, regulation of transcription from RNA polymerase II promoter, and cell adhesion, displayed a rhythmic pattern. Given the enrichment in genes dedicated to cell adhesion and their daily changes in the pituitary, it is hypothesized that cell-cell interactions could be involved in the transmission of information between endocrine cells, allowing rhythmic hormone outputs to be controlled in a temporally precise manner.

Consequences of DJ-1 upregulation following p53 loss and cell transformation.

p53 is a tumor suppressor that responds to various stress signals by initiating cell-cycle arrest, senescence and apoptosis. Mutations of the p53 gene are found in over 50% of human tumors, highlighting the importance of p53 in tumor suppression. Numerous studies have reported on the interactions between p53, IGF-1-AKT and mTOR pathways as potentially explaining some of the tumor suppressive activities of p53. To further understand the basis of these interactions, we analyzed the involvement of DJ-1, an oncogene known to drive AKT-mediated cell survival, in the p53-AKT axis. In this study, we show that DJ-1 and p53 are tightly 'linked': p53 prevents the accumulation of DJ-1 protein, whereas loss of p53 leads to stabilization and enhancement of DJ-1 expression. Interestingly, this increase in DJ-1 level is only observed when p53 loss is accompanied by transformation of cells. Moreover, DJ-1 seems to be required for the enhanced activation of AKT observed in p53-deficient cells. Such observation confers a new property to DJ-1 associated to transforming-process to its oncogenic ability to drive AKT activation. We also show that DJ-1 is necessary for p53 activation following oxidative stress, suggesting the existence of a finely regulated loop between these two proteins in transformed cells. Finally, we demonstrate that in the absence of p53, DJ-1 is stabilized by ROS accumulation, and surprisingly seems to be required for this high intracellular ROS production. These data offer new insights into the regulation of DJ-1 and suggest that DJ-1 is a target of p53. Importantly, our study highlights that during transformation, DJ-1 is having a key role in the p53-regulated AKT pathway and p53-driven oxidative-stress response.

Vitamin A is a necessary factor for sympathetic-independent rhythmic activation of mitogen-activated protein kinase in the rat pineal gland.

The circadian clock in the suprachiasmatic nucleus (SCN) controls day-to-day physiology and behavior by sending timing messages to multiple peripheral oscillators. In the pineal gland, a major SCN target, circadian events are believed to be driven exclusively by the rhythmic release of norepinephrine from superior cervical ganglia (SCG) neurons relaying clock messages through a polysynaptic pathway. Here we show in rat an SCN-driven daily rhythm of pineal MAPK activation that is not dependent on the SCG and whose maintenance requires vitamin A as a blood-borne factor. This finding challenges the dogma that SCG-released norepinephrine is an exclusive mediator of SCN-pineal communication and allows the assumption that humoral mechanisms are involved in pineal integration of temporal messages.

Adrenergic inducibility of AP-1 binding in the rat pineal gland depends on prior photoperiod.

The main known function of the pineal gland in mammals is the temporal synchronization of physiological rhythms to seasonal changes of day length (photoperiod). In rat, the transcription factor activating protein-1 (AP-1) displays a circadian rhythm in its DNA binding in the pineal gland, which results from the rhythmic expression of Fra-2. We postulated that, if AP-1 is an important component of pineal gland functioning, then variations in photoperiodic conditions should lead to an adaptation of the AP-1 binding rhythm. Here we show that AP-1 binding patterns adapt to variations in lighting conditions, in the same way as the rhythm of arylalkylamine-N-acetyltransferase (AA-NAT) activity. This adaptation appeared to result from photoperiodic adaptation of the rhythmic fra-2 gene expression and was reflected by an adapted delay between the onset of night and the acrophase of the nocturnal peak. We further showed that photoperiodic adaptation of both the AP-1 binding and AA-NAT activity rhythms resulted from adapted changes in adrenergic inducibility of both variables at night onset. We finally provided evidence that AP-1 shared with the CREM gene encoding the transcriptional repressor protein inducible cAMP early repressor (ICER) the ability to be hypersensitive or subsensitive to adrenergic stimuli, depending on prior photoperiod.

Circadian binding activity of AP-1, a regulator of the arylalkylamine N-acetyltransferase gene in the rat pineal gland, depends on circadian Fra-2, c-Jun, and Jun-D expression and is regulated by the clock's zeitgebers.

The daily rhythm in circulating melatonin is driven by a circadian rhythm in the expression of the arylalkylamine N:-acetyltransferase gene in the rat pineal gland. Turning off expression of this gene at the end of night is believed to involve inhibitory transcription factors, among which Fos-related antigen 2 (Fra-2) appears as a good candidate. Circadian rhythms in the expression of three proteins of activating protein-1 (AP-1) complexes, namely, Fra-2, c-Jun, and Jun-D, are shown here to account for circadian variations in AP-1 binding activity. Quantitative variations in the Fra-2 component over the circadian cycle were associated with qualitative variations in protein isoforms. Destruction of the suprachiasmatic nucleus resulted in decreased nocturnal AP-1 activity, showing that AP-1 circadian rhythm is driven by this nucleus. Exposure to light during subjective night and administration of a serotonin 5-HT(1A)/5-HT(7) receptor agonist during subjective day, respectively, induced a 50% decrease and a 50% increase in both AP-1 and Fra-2 expression. These effects were impaired by suprachiasmatic nucleus lesions. These data show that pineal AP-1 binding activity, which results from Fra-2 expression, can be modulated by light and serotonin through the suprachiasmatic nucleus according to a "phase dependence" that is characteristic of the rhythm of clock sensitivity to both zeitgebers.