Stimulation of GHRH Neuron Axon Growth by Leptin and Impact of Nutrition during Suckling in Mice.

Nutrition during the early postnatal period can program the growth trajectory and adult size. Nutritionally regulated hormones are strongly suspected to be involved in this physiological regulation. Linear growth during the postnatal period is regulated by the neuroendocrine somatotropic axis, whose development is first controlled by GHRH neurons of the hypothalamus. Leptin that is secreted by adipocytes in proportion to fat mass is one of the most widely studied nutritional factors, with a programming effect in the hypothalamus. However, it remains unclear whether leptin stimulates the development of GHRH neurons directly. Using a Ghrh-eGFP mouse model, we show here that leptin can directly stimulate the axonal growth of GHRH neurons in vitro in arcuate explant cultures. Moreover, GHRH neurons in arcuate explants harvested from underfed pups were insensitive to the induction of axonal growth by leptin, whereas AgRP neurons in these explants were responsive to leptin treatment. This insensitivity was associated with altered activating capacities of the three JAK2, AKT and ERK signaling pathways. These results suggest that leptin may be a direct effector of linear growth programming by nutrition, and that the GHRH neuronal subpopulation may display a specific response to leptin in cases of underfeeding.

Hereditary Diffuse Gastric Cancer.

Hereditary diffuse gastric cancer (HDGC) is a dominantly inherited cancer syndrome characterized by a high incidence of diffuse gastric cancer (DGC) and lobular breast cancer (LBC). HDGC is caused by germline mutations in 2 genes involved in the epithelial adherens junction complex, CDH1 and CTNNA1. We discuss the genetics of HDGC and the variability of its clinical phenotype, in particular the variable penetrance of advanced DGC and LBC, both within and between families. We review the pathology of the disease, the mechanism of tumor initiation, and its natural history. Finally, we describe current best practice for the clinical management of HDGC, including emerging genetic testing criteria for the identification of new families, methods for endoscopic surveillance, the complications associated with prophylactic surgery, postoperative quality of life, and the emerging field of HDGC chemoprevention.

E-Cadherin-Deficient Cells Are Sensitive to the Multikinase Inhibitor Dasatinib.

The CDH1 gene, encoding the cell adhesion protein E-cadherin, is one of the most frequently mutated genes in gastric cancer and inactivating germline CDH1 mutations are responsible for the cancer syndrome hereditary diffuse gastric cancer (HDGC). CDH1-deficient gastric cancers exhibit high AKT serine/threonine kinase 3 (AKT3) expression, but specific drugs against this AKT isoform are not available. We therefore used two publicly available datasets to identify AKT3-associated genes which could be used to indirectly target AKT3. Reactome analysis identified an enrichment of extracellular matrix remodelling genes in AKT3-high gastric cancers. Of the 51 genes that were significantly correlated with AKT3 (but not AKT1), discoidin domain receptor tyrosine kinase 2 (DDR2) showed the strongest positive association. Treatment of isogenic human cells and mouse gastric and mammary organoids with dasatinib, a small molecule inhibitor of multiple kinases including SRC, BCR-ABL and DDR2, preferentially slowed the growth and induced apoptosis of E-cadherin-deficient cells. Dasatinib treatment also preferentially slowed the growth of gastric and mammary organoids harbouring both Cdh1 and Tp53 mutations. In organoid models, dasatinib treatment was associated with decreased phosphorylation of total AKT, with a stronger effect seen in Cdh1-deficient organoids. Treatment with combinations of dasatinib and an inhibitor of AKT, MK2206, enhanced the effect of dasatinib in breast MCF10A cells. In conclusion, targeting the DDR2-SRC-AKT3 axis with dasatinib represents a promising approach for the chemoprevention and chemotherapy of gastric and breast cancers lacking E-cadherin.

E-Cadherin-Deficient Epithelial Cells Are Sensitive to HDAC Inhibitors.

Inactivating germline mutations in the CDH1 gene (encoding the E-cadherin protein) are the genetic hallmark of hereditary diffuse gastric cancer (HDGC), and somatic CDH1 mutations are an early event in the development of sporadic diffuse gastric cancer (DGC) and lobular breast cancer (LBC). In this study, histone deacetylase (HDAC) inhibitors were tested for their ability to preferentially inhibit the growth of human cell lines (MCF10A and NCI-N87) and murine organoids lacking CDH1 expression. CDH1-/- breast and gastric cells were more sensitive to the pan-HDAC inhibitors entinostat, pracinostat, mocetinostat and vorinostat than wild-type cells, with an elevated growth inhibition that was, in part, attributable to increased apoptosis. CDH1-null cells were also sensitive to more class-specific HDAC inhibitors, but compared to the pan-inhibitors, these effects were less robust to genetic background. Increased sensitivity to entinostat was also observed in gastric organoids with both Cdh1 and Tp53 deletions. However, the deletion of Tp53 largely abrogated the sensitivity of the Cdh1-null organoids to pracinostat and mocetinostat. Finally, entinostat enhanced Cdh1 expression in heterozygous Cdh1+/- murine organoids. In conclusion, entinostat is a promising drug for the chemoprevention and/or treatment of HDGC and may also be beneficial for the treatment of sporadic CDH1-deficient cancers.