RESUMEN
Leptin acts on its receptor (ObR) in the hypothalamus to inhibit food intake and energy expenditure. Leptin and ObR are also expressed in the gastrointestinal tract; however, the physiological significance of leptin signaling in the gut remains uncertain. Suppressor of cytokine signaling 3 (SOCS3) is a key negative feedback regulator of ObR-mediated signaling in the hypothalamus. We now show that gastrointestinal epithelial cell-specific SOCS3 conditional knockout (T3b-SOCS3 cKO) mice developed gastric tumors by enhancing leptin production and the ObRb/signal transducer and activator of transcription 3 (STAT3) signaling pathway. All T3b-SOCS3 cKO mice developed tumors in the stomach but not in the bowels by 2 months of age, even though the SOCS3 deletion occurred in both the epithelium of stomach and bowels. The tumors developed in the absence of the inflammatory response and all cKO mice died within 6 months. These tumors displayed pathology and molecular alterations, such as an increase in MUC2 (Mucin 2, oligomeric mucus/gel-forming) and TFF3 (trefoil factor 3), resembling human intestinal-type gastric tumors. Administration of antileptin antibody to T3b-SOCS3 cKO mice reduced hyperplasia of gastric mucosa, which is the step of the initiation of gastric tumor. These data suggest that SOCS3 is an antigastric tumor gene that suppresses leptin overexpression and ObRb/STAT3 hyperactivation, supporting the hypothesis that the leptin/ObRb/STAT3 axis accelerates tumorigenesis and that it may represent a new therapeutic target for the treatment of gastric cancer.
Asunto(s)
Adenocarcinoma/metabolismo , Receptores de Leptina/metabolismo , Neoplasias Gástricas/metabolismo , Proteínas Supresoras de la Señalización de Citocinas/deficiencia , Adenocarcinoma/tratamiento farmacológico , Animales , Anticuerpos/administración & dosificación , Antineoplásicos/administración & dosificación , Carcinogénesis/metabolismo , Células Cultivadas , Modelos Animales de Enfermedad , Evaluación Preclínica de Medicamentos , Mucosa Gástrica/metabolismo , Humanos , Inyecciones Intraperitoneales , Mucosa Intestinal/metabolismo , Leptina/antagonistas & inhibidores , Leptina/inmunología , Ratones , Ratones Transgénicos , Neoplasias Experimentales/tratamiento farmacológico , Neoplasias Experimentales/metabolismo , Proteínas Quinasas/metabolismo , Factor de Transcripción STAT3/metabolismo , Transducción de Señal , Estómago/patología , Neoplasias Gástricas/tratamiento farmacológico , Proteína 3 Supresora de la Señalización de Citocinas , Proteínas Supresoras de la Señalización de Citocinas/genéticaRESUMEN
A systematic method of extraction, fractionation, and purification of polysaccharides from Songshan Lingzhi (Ganoderma tsugae) with antitumor activity was established. Seven glycans with strong antitumor activities were obtained from 14 water-soluble, and 15 water-insoluble fractions: FIo-a, FA-1, FII-1, FIII-2, and FIII-2-a, -b, and -c. FIo-a and FA-1 were protein-containing glucogalactans associated with mannose and fucose. FII-1 was a (1-->3)-beta-D-glucan having a lower protein content. The water-insoluble fractions FIII-2-a, -b, and -c were extracted with alkali, and were found to be protein-containing (1-->3)-beta-D-glucans showing the strongest activity. Chemical properties and structure of each antitumor polysaccharide were compared with three fungi of the Ganoderma family, Kofukitake (G. applanatum), Mannentake (G. lucidum), and Songshan Lingzhi (G. tsugae).