Targeting protein palmitoylation decreases palmitate­induced sphere formation of human liver cancer cells.

Although non­alcoholic fatty liver disease (NAFLD) is considered a benign disorder, hepatic steatosis has been proposed to be involved in the tumorigenesis of liver cancer. However, the underlying mechanism for carcinogenesis in fatty liver diseases remains unclear. Cancer stem cells (CSCs) have been hypothesized to serve a key role in tumorigenesis. Tumor formation begins with a subset of heterogeneous cells that share properties with stem cells, such as self­renewal and undifferentiated properties. Our previous study reported that the saturated fatty acid palmitate (PA) significantly enhanced the CSC properties of the HepG2 human liver cancer cell line; however, its underlying mechanisms are unknown. In the present study, a proteomic approach was used to investigate the palmitoylation of proteins in HepG2 CSCs. CSC behavior was induced in HepG2 cells via 200 µM PA. Proteomic analysis was performed to identify post­transcriptional modifications of proteins in HepG2 CSCs in response to PA treatment. The present study identified proteins modified by palmitoylation in HepG2 CSC spheres formed following PA treatment. It was therefore hypothesized that palmitoylation may be crucial for CSC sphere formation. Furthermore, the present study demonstrated that two palmitoylation inhibitors, tunicamycin (5, 10 and 25 µg/ml) and 2­bromohexadecanoic acid (25, 50 and 150 µM), significantly decreased CSC sphere formation without affecting cell viability. An association was identified between sphere formation capacity and tumor­initiating capacity of CSCs. The results of the present study demonstrated that protein palmitoylation may influence the PA­induced CSC tumor­initiating capacity, and that the inhibition of palmitoylation may be a suitable chemopreventive strategy for treating patients with NAFLD.

Molecular diagnosis of colorectal tumors by expression profiles of 50 genes expressed differentially in adenomas and carcinomas.

Most colon cancers are thought to develop through the 'adenoma-to-carcinoma sequence' model. To elucidate the mechanisms underlying this pathway, we analysed gene-expression profiles of 20 colorectal tumors (nine adenomas and 11 differentiated adenocarcinomas) by means of a cDNA microarray representing 23,040 genes coupled with laser-capture microdissection. A two-dimensional hierarchical clustering analysis of expression profiles of the 20 tumors correctly separated the carcinoma group from the adenoma group. Furthermore we identified 51 genes whose expression was commonly up-regulated, 376 that were commonly down-regulated in both types of tumors as opposed to normal colonic epithelium and 50 whose expression levels were significantly different between adenomas and carcinomas. On the basis of expression profiles of the 50 discriminating genes, we established a scoring system to separate adenomas from carcinomas. Application of this scoring system for evaluating five additional colorectal tumors correctly predicted their histological features. The genome-wide information reported here should contribute to a more profound understanding of colorectal tumorigenesis, particularly of adenoma-carcinoma progression, and provide indicators for developing novel strategies to diagnose, treat, and ultimately prevent colorectal carcinomas.