RESUMEN
Kokumi taste is a well-accepted and characterised taste modality and is described as a sensation of enhancement of sweet, salty, and umami tastes. The Calcium Sensing Receptor (CaSR) has been designated as the putative kokumi taste receptor for humans, and a number of kokumi-active ligands of CaSR have been discovered recently with activity confirmed both in vivo and in vitro. Domestic cats (Felis catus) are obligate carnivores and accordingly, their diet is abundant in proteins, peptides, and amino acids. We hypothesised that CaSR is a key taste receptor for carnivores, due to its role in the detection of different peptides and amino acids in other species. Using in silico, in vitro and in vivo approaches, here we compare human CaSR to that of a model carnivore, the domestic cat. We found broad similarities in ligand specificity, but differences in taste sensitivity between the two species. Indeed our in vivo data shows that cats are sensitive to CaCl2 as a kokumi compound, but don't show this same activity with Glutathione, whereas for humans the reverse is true. Collectively, our data suggest that kokumi is an important taste modality for carnivores that drives the palatability of meat-derived compounds such as amino acids and peptides, and that there are differences in the perception of kokumi taste between carnivores and omnivores.
Asunto(s)
Gatos/fisiología , Percepción del Gusto , Secuencia de Aminoácidos , Aminoácidos/análisis , Animales , Cloruro de Calcio/metabolismo , Glutatión/metabolismo , Humanos , Ligandos , Cloruro de Magnesio/metabolismo , Productos de la Carne/análisis , Péptidos/análisis , Unión Proteica , Receptores Sensibles al Calcio/metabolismo , Papilas Gustativas/metabolismoRESUMEN
Oncogenic RAS promotes production of reactive oxygen species (ROS), which mediate pro-malignant signaling but can also trigger DNA damage-induced tumor suppression. Thus RAS-driven tumor cells require redox-protective mechanisms to mitigate the damaging aspects of ROS. Here, we show that MutT Homolog 1 (MTH1), the mammalian 8-oxodGTPase that sanitizes oxidative damage in the nucleotide pool, is important for maintaining several KRAS-driven pro-malignant traits in a nonsmall cell lung carcinoma (NSCLC) model. MTH1 suppression in KRAS-mutant NSCLC cells impairs proliferation and xenograft tumor formation. Furthermore, MTH1 levels modulate KRAS-induced transformation of immortalized lung epithelial cells. MTH1 expression is upregulated by oncogenic KRAS and correlates positively with high KRAS levels in NSCLC human tumors. At a molecular level, in p53-competent KRAS-mutant cells, MTH1 loss provokes DNA damage and induction of oncogene-induced senescence. In p53-nonfunctional KRAS-mutant cells, MTH1 suppression does not produce DNA damage but reduces proliferation and leads to an adaptive decrease in KRAS expression levels. Thus, MTH1 not only enables evasion of oxidative DNA damage and its consequences, but can also function as a molecular rheostat for maintaining oncogene expression at optimal levels. Accordingly, our results indicate MTH1 is a novel and critical component of oncogenic KRAS-associated malignancy and its inhibition is likely to yield significant tumor-suppressive outcomes in KRAS-driven tumors.
Asunto(s)
Carcinoma de Pulmón de Células no Pequeñas/metabolismo , Daño del ADN , Enzimas Reparadoras del ADN/biosíntesis , Regulación Neoplásica de la Expresión Génica , Neoplasias Pulmonares/metabolismo , Monoéster Fosfórico Hidrolasas/biosíntesis , Proteínas Proto-Oncogénicas/metabolismo , Proteínas ras/metabolismo , Animales , Carcinoma de Pulmón de Células no Pequeñas/genética , Carcinoma de Pulmón de Células no Pequeñas/patología , Proliferación Celular/genética , Enzimas Reparadoras del ADN/genética , Femenino , Humanos , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/patología , Masculino , Ratones , Ratones Desnudos , Monoéster Fosfórico Hidrolasas/genética , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas p21(ras) , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/metabolismo , Regulación hacia Arriba , Proteínas ras/genéticaRESUMEN
Approximately 20% of tumors contain activating mutations in the RAS family of oncogenes. As tumors progress to higher grades of malignancy, the expression of oncogenic RAS has been reported to increase, leading to an oncogene-induced senescence (OIS) response. Evasion of this senescence barrier is a hallmark of advanced tumors indicating that OIS serves a critical tumor-suppressive function. Induction of OIS has been attributed to either RAS-mediated production of reactive oxygen species (ROS) or to induction of a DNA damage response (DDR). However, functional links between these two processes in triggering the senescent phenotype have not been explicitly described. Our previous work has shown that, in cultured untransformed cells, preventing elimination of oxidized guanine deoxyribonucleotides, which was achieved by suppressing expression of the cellular 8-oxo-dGTPase, human MutT homolog 1 (MTH1), sufficed to induce a DDR as well as premature senescence. Here, we demonstrate that overexpression of MTH1 can prevent the oncogenic H-RAS-induced DDR and attendant premature senescence, although it does not affect the observed elevation in ROS levels produced by RAS oncoprotein expression. Conversely, we find that loss of MTH1 preferentially induces an in vitro proliferation defect in tumorigenic cells overexpressing oncogenic RAS. These results indicate that the guanine nucleotide pool is a critical target for intracellular ROS produced by oncogenic RAS and that RAS-transformed cells require robust MTH1 expression to proliferate.
Asunto(s)
Daño del ADN/genética , Enzimas Reparadoras del ADN/biosíntesis , Genes ras , Nucleótidos de Guanina/metabolismo , Monoéster Fosfórico Hidrolasas/biosíntesis , Línea Celular , Proliferación Celular , Senescencia Celular/genética , Humanos , Oxidación-Reducción , Especies Reactivas de Oxígeno/metabolismoRESUMEN
The vertebrate Otx gene family is related to otd, a gene contributing to head development in Drosophila. We previously reported on the expression of Xotx2 gene, homologous to the murine Otx2 gene, during early Xenopus development. In the present paper we report an extensive analysis of the expression pattern of Xotx2 during later stages of development and also the cloning and developmental expression of two additional Otx Xenopus genes, Xotx1 and Xotx4. These latter two genes bear a good degree of homology to murine Otx1, higher for Xotx1 than for Xotx4. Both these genes are expressed in the forebrain and midbrain regions and their developmental patterns of expression are very similar, although not perfectly superimposable. Spatial and temporal expression patterns of the three Xotx genes suggest that they may be involved in the early subdivision of the rostral brain, providing antero-posterior positional information within the most anterior districts of the neuraxis. The three Xotx genes are expressed in all the developing sense organs of the head, eyes, olfactory system and otic vesicles. By in situ hybridization the earliest detectable expression is found in anterior mesendoderm for Xotx2, and in presumptive anterior neuroectoderm for Xotx1 and Xotx4. In addition, we examined whether Xotx1 is expressed in exogastrulae, finding that Xotx1 expression can be activated in the apparent absence of vertical signals of neural induction.