Christophe Mas

Melanomas require HEDGEHOG-GLI signaling regulated by interactions between GLI1 and the RAS-MEK/AKT pathways

Melanoma is one of the most aggressive cancers, and its incidence is increasing. These tumors derive from the melanocyte lineage and remain incurable after metastasis. Here we report that SONIC HEDGEHOG (SHH)-GLI signaling is active in the matrix of human hair follicles, and that it is required for the normal proliferation of human melanocytes in culture. SHH-GLI signaling also regulates the proliferation and survival of human melanomas: the growth, recurrence, and metastasis of melanoma xenografts in mice are prevented by local or systemic interference of HH-GLI function. Moreover, we show that oncogenic RAS-induced melanomas in transgenic mice express Gli1 and require Hh-Gli signaling in vitro and in vivo. Finally, we provide evidence that endogenous RAS-MEK and AKT signaling regulate the nuclear localization and transcriptional activity of GLI1 in melanoma and other cancer cells. Our data uncover an unsuspected role of HH-GLI signaling in melanocytes and melanomas, demonstrate a role for this pathway in RAS-induced tumors, suggest a general integration of the RAS/AKT and HH-GLI pathways, and open a therapeutic approach for human melanomas.

Human colon cancer epithelial cells harbour active HEDGEHOG-GLI signalling that is essential for tumour growth, recurrence, metastasis and stem cell survival and expansion

Human colon cancers often start as benign adenomas through loss of APC, leading to enhanced βCATENIN (βCAT)/TCF function. These early lesions are efficiently managed but often progress to invasive carcinomas and incurable metastases through additional changes, the nature of which is unclear. We find that epithelial cells of human colon carcinomas (CCs) and their stem cells of all stages harbour an active HH‐GLI pathway. Unexpectedly, they acquire a high HEDGEHOG‐GLI (HH‐GLI) signature coincident with the development of metastases. We show that the growth of CC xenografts, their recurrence and metastases require HH‐GLI function, which induces a robust epithelial‐to‐mesenchymal transition (EMT). Moreover, using a novel tumour cell competition assay we show that the self‐renewal of CC stem cells in vivo relies on HH‐GLI activity. Our results indicate a key and essential role of the HH‐GLI1 pathway in promoting CC growth, stem cell self‐renewal and metastatic behavior in advanced cancers. Targeting HH‐GLI1, directly or indirectly, is thus predicted to decrease tumour bulk and eradicate CC stem cells and metastases.

Small molecule modulation of HH-GLI signaling: current leads, trials and tribulations.

Many human sporadic cancers have been recently shown to require the activity of the Hedgehog-GLI pathway for sustained growth. The survival and expansion of cancer stem cells is also HH-GLI dependent. Here we review the advances on the modulation of HH-GLI signaling by small molecules. We focus on both natural compounds and synthetic molecules that target upstream pathway components, mostly SMOOTHENED, and those that target the last steps of the pathway, the GLI transcription factors. In this review we have sought to provide some bases for useful comparisons, listing original assays used and sources to facilitate comparisons of IC50 values. This area is a rapidly expanding field where biology, medicine and chemistry intersect, both in academia and industry. We also highlight current clinical trials, with positive results in early stages. While we have tried to be exhaustive regarding the molecules, not all data is in the public domain yet. Indeed, we have opted to avoid listing chemical structures but these can be easily found in the references given. Finally, we are hopeful that the best molecules will soon reach the patients but caution about the lack of investment on compounds that lack tight IP positions. While the market in developed nations is expected to compensate the investment and risk of making HH-GLI modulators, other sources or plans must be available for developing nations and poor patient populations. The promise of curing cancer recalls the once revered dream of El Dorado, which taught us that not everything that GLI-tters is gold.

Sequential activation of p75 and TrkB is involved in dendritic development of subventricular zone-derived neuronal progenitors in vitro

Dendritic arbor development of subventricular zone‐derived interneurons is a critical step in their integration into functional circuits of the postnatal olfactory bulb. However, the mechanism and molecular control of this process remain unknown. In this study, we have developed a culture model where dendritic development of purified subventricular zone cells proceeds under serum‐free conditions in the absence of added growth factors and non‐neural cells. We demonstrate that the large majority of these cells in culture express GABA and elaborate dendritic arbors with spine‐like protrusions but they do not possess axons. These neurons expressed receptors for neurotrophins including p75, TrkB and TrkC but not TrkA. Application of exogenous neurotrophins, including brain‐derived neurotrophic factor (BDNF), neurotrophin‐3 (NT3) and nerve growth factor (NGF), to cultures stimulated dendritic growth and led to more complex dendritic arbors during the initial 3 days in culture. Our results suggest that these effects are independent of Trk receptors and mediated by the p75/ceramide signaling pathway. We also show that brain‐derived neurotrophic factor is the only neurotrophin that is able to influence late‐phase dendritic development via TrkB receptor activation. These results suggest that dendritic arbor development of subventricular zone‐derived cells may be regulated by neurotrophins through the activation of p75 and the TrkB receptor signaling pathways in a sequentially defined temporal pattern.

Association of the connexin36 gene with juvenile myoclonic epilepsy

Epilepsy is one of the most common and serious neurological disorders, with up to 60 million people affected worldwide.1 Juvenile myoclonic epilepsy (JME) is a common familial form that accounts for 5–10% of all epilepsy cases.2 This form belongs to the idiopathic epilepsy group, due to the absence of detectable structural or metabolic abnormalities. Clinically, JME is mainly characterised by isolated myoclonic jerks on awakening that usually begin during adolescence. It is also highly drug-dependent, since a 90% recurrence is reported after interruption of pharmacological treatment.3 Studies on the incidence of epilepsy in relatives of probands with JME, as well as on twins, have provided strong evidence for a genetic contribution.4,5 Autosomal dominant, autosomal recessive, two locus, monogenic, and polygenic models of inheritance have been suggested.6 So far, three genes that are mutated in different forms of JME have been identified, namely CACNB4 ,7 GABRA1 ,8 and CLCN2 .9 In addition, two different susceptibility loci have been identified by linkage analysis. The first locus, termed EJM1 (OMIM 254770), is on the human leukocyte antigen region of chromosome 6p.10 Although no trait-causing mutation has yet been identified at this locus, association with a haplotype of the BRD2 gene has been recently reported.11 The second locus, termed EJM2 (OMIM 604827), is in the region of chromosome 15q that contains the gene coding for the α7-nicotinic acetylcholine receptor subunit. Genetic mapping of the EJM2 locus defined a 15.1 cM candidate region on chromosome 15q14, flanked by the D15S165 and D15S971 loci.6 Interestingly, this region includes the CX36 gene, which codes for the first connexin identified in neurons.12 Connexins are integral membrane proteins, encoded by a family of at least 20 genes in humans, which form the subunits of gap junction …

Connexins and secretion.

Summry— Connexin channels clustered at gap junctions are obligatory attributes of all macroscopic endocrine and exocrine glands investigated so far and also connect most types of cells which produce secretory products in other tissues. Increasing evidence indicates that connexins, and the cell‐to‐cell communications that these proteins permit, contribute to control the growth of secretory cells, their expression of specific genes and their differentiated function, including their characteristic ability to biosynthetize and release secretory products in a regulated manner. Since the previous reviews which have been published on this topic, several lines of evidence have been added in support of multiple regulatory roles of gland connexins. Here, we review this novel evidence, point to the many questions which are still open and discuss some interesting perspectives of the field.

Ventilatory responses to hypercapnia and hypoxia in Mash-1 heterozygous newborn and adult mice.

Normal control of breathing is characterized by maintenance of CO2 and O2 arterial pressures at constant levels by appropriate ventilatory responses to changes in CO2 production and O2 consumption. Abnormal development of this regulatory system during embryogenesis may produce early impairments in chemosensitivity, as in congenital central hypoventilation syndrome. The present study addresses the role of the mammalian achaete-scute homologous gene (Mash-1) in the development of respiratory control. We analyzed ventilatory responses to hypercapnia (8% CO2, 21% O2, 71% N2) and hypoxia (10% O2, 3% CO2, 87% N2) in newborn and adult Mash-1 heterozygous mice (Mash-1+/−) and their wild-type littermates (Mash-1+/+). Ventilation, breath duration, and tidal volume were measured using whole-body plethysmography. Ventilatory responses to hypercapnia were significantly weaker in newborn male Mash-1+/− compared with Mash-1+/+ mice as a result of a weaker breath-duration response. No differences were observed between adult Mash-1+/− and Mash-1+/+ mice. Our data suggest that Mash-1 may be involved in respiratory control development via mechanisms linked to the X chromosome.

Survival motor neuron SMN1 and SMN2 gene promoters: identical sequences and differential expression in neurons and non-neuronal cells

Spinal muscular atrophy (SMA) is a recessive disorder involving the loss of motor neurons from the spinal cord. Homozygous absence of the survival of motor neuron 1 gene (SMN1) is the main cause of SMA, but disease severity depends primarily on the number of SMN2 gene copies. SMN protein levels are high in normal spinal cord and much lower in the spinal cord of SMA patients, suggesting neuron-specific regulation for this ubiquitously expressed gene. We isolated genomic DNA from individuals with SMN1 or SMN2 deletions and sequenced 4.6 kb of the 5′ upstream regions of the these. We found that these upstream regions, one of which is telomeric and the other centromeric, were identical. We investigated the early regulation of SMN expression by transiently transfecting mouse embryonic spinal cord and fibroblast primary cultures with three transgenes containing 1.8, 3.2 and 4.6, respectively, of the SMN promoter driving β-galactosidase gene expression. The 4.6 kb construct gave reporter gene expression levels five times higher in neurons than in fibroblasts, due to the combined effects of a general enhancer and a non-neuronal cell silencer. The differential expression observed in neurons and fibroblasts suggests that the SMN genes play a neuron-specific role during development. An understanding of the mechanisms regulating SMN promoter activity may provide new avenues for the treatment of SMA.

Lentivirus-mediated transduction of connexin cDNAs shows level- and isoform-specific alterations in insulin secretion of primary pancreatic beta-cells

We have generated novel lentiviral vectors to integrate various connexin cDNAs into primary, non-dividing cells. We have used these vectors to test whether proper control of insulin secretion depends on a specific connexin isoform and/or on its level of expression. We have observed that transduced connexin32, connexin36 and connexin43 were expressed by primary adultβ -cells at membrane interfaces, were packed into typical gap junction plaques and formed functional channels that allowed a variable coupling, depending on the type and level of connexin expressed. The infected cells spontaneously reaggregated into three-dimensional pseudo-islet organs that could be maintained in culture. We have found that pseudo-islets made by cells transduced with either GFP- or connexin43-expressing lentivirus released insulin in response to various secretagogues similarly to controls. By contrast, pseudo-islets made by cells expressing connexin32, a connexin exogenous to pancreatic islets, or over-expressing connexin36, the endogenous islet connexin, featured a marked decrease in the secretory response to glucose. The data show: (1) that lentiviral vectors allow stable modulation of various connexin in primary, non-proliferating cells; (2) that specific connexin isoforms affect insulin secretion differently; and (3) that adequate levels of coupling via connexin36 channels are required for proper β-cell function.

General and Conditional Replacement of Connexin43-Coding DNA by a lacZ Reporter Gene for Cell-Autonomous Analysis of Expression

Using the Cre/loxP system, we have circumvented early postnatal lethality and possible pleiotropic effects of general Cx43 gene deletion, in order to determine the expression and function of connexin43 (Cx43) in defined cell types. General or cell type-specific, Cre-mediated deletion of the floxed (i.e. flanked by loxP sites) Cx43-coding region led to activation of the inserted lacZ reporter gene in cells with transcriptional activity of the Cx43 gene. As deduced from lacZ expression in mice with general deletion, transcriptional activity of the Cx43 gene was not only found in a broad range of cell types known to a express Cx43, but also in pancreatic duct cells and vascular cells of the gut and skeletal muscle. Cre-mediated deletion restricted to defined cell types led to lacZ activation highlighting corresponding subsets of cells expressing Cx43, such as vascular endothelial cells, hepatic duct cells and putative neural crest cells, which were otherwise masked by strong Cx43 expression in neighbouring cells. In Cx43 expressing cell types, the floxed Cx43 allele was useful as a Cre-excision reporter for the characterization of Cre transgenes.