Tumor progression is a multistep process in which proproliferation mutations must be accompanied by suppression of senescence. In melanoma, proproliferative signals are provided by activating mutations in NRAS and BRAF, whereas senescence is bypassed by inactivation of the p16 Ink4a gene. Melanomas also frequently exhibit constitutive activation of the Wnt/␤-catenin pathway that is presumed to induce proliferation, as it does in carcinomas. We show here that, contrary to expectations, stabilized ␤-catenin reduces the number of melanoblasts in vivo and immortalizes primary skin melanocytes by silencing the p16 Ink4a promoter. Significantly, in a novel mouse model for melanoma, stabilized ␤-catenin bypasses the requirement for p16 Ink4a mutations and, together with an activated N-Ras oncogene, leads to melanoma with high penetrance and short latency. The results reveal that synergy between the Wnt and mitogen-activated protein (MAP) kinase pathways may represent an important mechanism underpinning the genesis of melanoma, a highly aggressive and increasingly common disease.[Keywords: Mitf; Wnt; senescence; development; tumor suppressor; oncogene] Supplemental material is available at http://www.genesdev.org.

Background. Gastrointestinal motility and serum thyroid hormone levels are closely related. Our aim was to analyze whether there is a disorder in esophagogastric motor functions as a result of hypothyroidism. Materials and Methods. The study group included 30 females (mean age ± SE 45.17 ± 2.07 years) with primary hypothyroidism and 10 healthy females (mean age ± SE 39.40 ± 3.95 years). All cases underwent esophagogastric endoscopy and scintigraphy. For esophageal scintigraphy, dynamic imaging of esophagus motility protocol, and for gastric emptying scintigraphy, anterior static gastric images were acquired. Results. The mean esophageal transit time (52.56 ± 4.07 sec for patients; 24.30 ± 5.88 sec for controls; P = .02) and gastric emptying time (49.06 ± 4.29 min for the hypothyroid group; 30.4 ± 4.74 min for the control group; P = .01) were markedly increased in cases of hypothyroidism. Conclusion. Hypothyroidism prominently reduces esophageal and gastric motor activity and can cause gastrointestinal dysfunction.

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Primary mesenchymal tumors of the colon are extremely rare tumors among soft tissue sarcomas. These tumors are more aggressive and have poorer prognosis than adenocarcinoma of the colon. Here, we presented 3 cases of primary mesenchymal tumors of the colon. Their histopathological diagnoses are leiomyosarcoma, pleomorphic liposarcoma, and desmoplastic small round cell tumor, respectively. The rarity of primary mesenchymal tumors of the colon makes it difficult to approach the treatment and predict the prognosis of these rare tumors.

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