Altered Expression of Autophagy-related Genes in Human Colon Cancer

Abstract

Background and objectives: Autophagy is a physiologic mechanism, which utilizes the self-digestion of cell organelles to promote cellular homeostasis, such as in the setting of dysfunctional cellular components, cellular stress or energy-deprived states. In vitro studies have pointed toward the key role of autophagy in colorectal cancer. However, in vivo studies from human colorectal cancer tissues are lacking. Methods: We collected tissue samples from six patients with colon cancer who received curative surgery at Baylor College of Medicine. We also obtained normal colonic mucosa biopsy from five unrelated polyp-free individuals who were matched to cases individually by age, sex, ethnicity, and colon segment. Total RNA was successfully extracted from fresh frozen tissue biopsies of five tumor tissues and five unrelated normal tissues. We tested the expression levels of 84 genes in a predefined autophagy pathway using the RT2 Profiler PCR array. We compared differences using Student’s t-test. The false-discovery rate was used for multiple testing adjustment. We also used the TCGA dataset to validate our findings. Results: We observed significant differential expression between colon cancer tissue and normal colon mucosa for 29 genes in the autophagy pathway (p < 0.05). After multiple testing adjustment, the expression of 17 genes was significantly down-regulated, with fold-change greater than 2 in colon cancer; these included ATG4A, ATG4C, ATG4D, and CTSS (q < 0.10). The down-regulation was observed in both early and late stage colon cancer. We observed the same down-regulation of multiple autophagy-related genes using the TCGA data. The ATG9B gene was the only statistically non-significantly up-regulated gene after multiple testing adjustment. Conclusions: This pilot study showed the down-regulation of multiple autophagy pathway genes in human colon cancer, corroborating the increasing clinical relevance of autophagy in human colorectal carcinogenesis. This preliminary finding should be validated in larger studies.