When analyzing high density transcript profiles in normal/tumor colon tissues, we found that zymogen granule protein 16 (ZG-16) was the most significant down-regulated gene among all transcripts analyzed. We performed real-time quantitative RT-PCR in 25 pairs of normal/tumor colon tissues and confirmed significant down-regulation of the gene in these tumors. To further explore the expression levels of this gene, we generated a polyclonal antibody and performed immunohistochemistry analysis using tissue arrays. These arrays included a variety of normal tissues and tissues from patients with various diseases, which included 40 cases with colorectal cancers, 2 cases with Peutz-Jeghers syndrome, 3 cases with juvenile polyposis syndrome, 10 cases with adenomatous polyps, and 6 cases with chronic ulcerative colitis. We found that ZG-16 was expressed in an organ-specific manner: specifically, very high expression levels in normal epithelial cells of the small and large intestine and no or weak expression in other tissue types. Protein expression was predominantly localized to the top one-third of the colon crypt, suggesting that control of expression is linked to epithelial differentiation. We also found that expression of the ZG-16 was completely lost in all 40 colon cancers tested, and partially lost in the 3 hamartomatous polyps from juvenile polyposis syndrome, the 10 adenomatous polyps and the 6 tissues with chronic ulcerative colitis (4 with cancer, 2 without cancer), while remained unchanged in the 2 hamartomatous polyps from Peutz-Jeghers syndrome. The partial loss in adenomas demonstrated a unique distribution. For example, complete loss in one crypt was observed with normal expression in another. The partial loss in chronic ulcerative colitis displayed an evenly distributed weak signal along affected crypts. Protein sequence analysis of the gene showed that the putative protein had a signal peptide and a jacalin-like lectin domain, indicating that it is a secretory protein and has similar function with jackfruit jacalin. It has been reported that jacalin selectively stimulates CD4+ lymphocytes and specifically binds to IgA. Jacalin also displays strong affinity for Thomsen-Friedenreich antigen, an oncofetal protein, and inhibits the proliferation of colon cancer cells. Therefore, ZG-16 may play an important role in colon immunity and tumorigenesis. Further characterization of the protein will facilitate our understanding of colorectal cancer and may provide a new strategy for cancer prevention.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]