Search

The possible role of leptin in colorectal tumors has been investigated in previous studies; however, to date, the conclusions remain under debate. Therefore, we investigated the serum leptin levels in colorectal adenoma patients. In addition, expression of the leptin receptor, and the leptin receptor-mediated signaling pathways were investigated in biopsy specimens collected from human patients with colorectal adenoma. No significant difference in the mean serum leptin level was observed between the colorectal adenoma patients and the control subjects; however, increased expression and activation of the leptin receptor, as indicated by findings such as the phosphorylation of Tyr 1141, was observed in the colorectal adenoma tissues. In addition, activation of the JAK/STAT signaling pathway mediated by the leptin receptor and increased transcriptional regulation of downstream target molecules were observed in colorectal adenomas compared with the non-adenoma tissues. These results indicate STAT3-mediated leptin receptor signaling pathways may be activated in human colorectal adenomas. (Cancer Sci 2011; 102: 367–372)

The association between obesity and the risk of colorectal cancer (CRC) cannot be easily evaluated because CRC itself is associated with a gradual loss of bodyweight. Aberrant crypt foci (ACF) can be classified as dysplastic ACF or non-dysplastic ACF by magnifying colonoscopy, and dysplastic ACF are thought to be a biomarker of CRC. Ninety-four participants who underwent colonoscopy at Yokohama City University Hospital, Japan, were enrolled in the current study. We detected 557 ACF, including 67 dysplastic ACF (12.0%). Univariate regression analysis was conducted to determine correlations between the number of dysplastic ACF and various potential risk factors, including patient age, waist circumference, body mass index, visceral fat area (VFA), and plasma adiponectin level. The results of multiple regression analysis revealed that the number of dysplastic ACF correlated with age (correlation coefficient r=0.212, P=0.0383) and plasma adiponectin level (r=-0.201, P=0.0371), even after adjustments for sex, waist circumference, body mass index, and VFA. Our univariate correlation analysis data showed a significant correlation with the number of dysplastic ACF with VFA (r=0.238, P=0.0209), no correlation with subcutaneous fat area, and an inverse correlation with the plasma level of adiponectin (r=-0.258, P=0.0118). Thus, our results suggest that aging and visceral fat accumulation could correlate moderately with colorectal carcinogenesis. The novelty of our study lies in the finding that visceral fat accumulation and a low plasma adiponectin level may promote colorectal carcinogenesis; therefore, these obesity-related parameters may serve as novel targets for CRC prevention.

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor that has been implicated in the carcinogenesis and progression of various solid tumors, including pancreatic carcinomas. We aimed to clarify the role of this receptor in pancreatic cell motility in vitro and in metastasis in vivo. Cell motility was examined by assaying transwell migration and wound filling in Capan-1 and Panc-1 pancreatic cancer cells, with or without the PPARgamma-specific inhibitor T0070907. A severe combined immunodeficiency xenograft metastasis model was used to examine the in vivo effect of PPARgamma inhibition on pancreatic cancer metastasis. In both transwell-migration and wound-filling assays, inhibition of PPARgamma activity suppressed pancreatic cell motility without affecting in vitro cell proliferation. Inhibition of PPARgamma also suppressed liver metastasis in vivo in metastatic mice. In PPARgamma-inhibited cells, p120 catenin accumulation was induced predominantly in cell membranes, and the Ras-homologous GTPases Rac1 and Cdc42 were inactive. Inhibition of PPARgamma in pancreatic cancer cells decreased cell motility by altering p120ctn localization and by suppressing the activity of the Ras-homologous GTPases Rac1 and Cdc42. Based on these findings, PPARgamma could function as a novel target for the therapeutic control of cancer cell invasion or metastasis.