Effects of Gut-Targeted 15-LOX-1 Transgene Expression on Colonic Tumorigenesis in Mice

Abstract

Expression of 15-lipoxygenase-1 (15-LOX-1) is decreased in many human cancers; however, the mechanistic significance of its decreased expression has been difficult to determine because its mouse homolog 12/15-LOX has opposing functions. We generated a mouse model in which expression of a human 15-LOX-1 transgene was targeted to the intestinal epithelium via the villin promoter. Targeted expression was confirmed by real-time reverse transcription-polymerase chain reaction and immunoblotting. When the 15-LOX-1 transgene was expressed in colonic epithelial cells of two independent mouse lines (B6 and FVB), azoxymethane-inducible colonic tumorigenesis was suppressed (mean number of tumors: wild type [WT] = 8.2, 15-LOX-1(+/-) = 4.91, 15-LOX-1(+/+) = 3.57; WT vs 15-LOX-1(+/-) two-sided P = .003, WT vs 15-LOX-1(+/+) two-sided P < .001; n = 10-14 mice per group). 15-LOX-1 transgene expression was always decreased in the tumors that did develop. In the presence of expression of the 15-LOX-1 transgene, expression of tumor necrosis factor alpha and its target inducible nitric oxide synthase were decreased and activation of nuclear factor-kappa B in colonic epithelial cells was inhibited.

ALOX15 as a suppressor of inflammation and cancer: Lost in the link

“…Downregulation of ALOX15 expression in human colorectal cancer cells is associated with upregulation of IL-1β, and re-expression of ALOX15 in colon cancer cells suppresses IL-1β expression [31]. Furthermore, transgenic expression of human ALOX15 in mouse colonic epithelial cells inhibits TNF-α and nuclear factor kappa B (NF-κB) signaling [32]. …”

“…Loss of ALOX15 expression is transcriptionally mediated [81] and independent of substrate availability [31]. While some earlier studies suggested that ALOX15 might have a procarcinogenic role, several lines of evidence, including more recent evidence [32, 82] have demonstrated that ALOX15 has a tumor-suppressing role, especially in colorectal tumorigenesis [74, 83]. ALOX15 re-expression in human colorectal cancer cells via pharmaceutical agents [21, 84, 85] or plasmid or adenoviral vectors [20, 70, 73] inhibits the growth of those cells in vitro and in vivo [86].…”

“…ALOX15 re-expression in human colorectal cancer cells via pharmaceutical agents [21, 84, 85] or plasmid or adenoviral vectors [20, 70, 73] inhibits the growth of those cells in vitro and in vivo [86]. Transgenic expression of human ALOX15 in mouse colonocytes (ALOX15-Gut mice) inhibits colorectal tumorigenesis [32]. ALOX15 expression in ALOX15-Gut mice inhibits NF-κB activation and azoxymethane-induced colorectal tumorigenesis [32] and colitis-associated colorectal tumorigenesis [82].…”

The role of 15-LOX-1 in colitis and colitis-associated colorectal cancer

“…15-LOX-1 transgene expression was always decreased in the tumors that did develop. In the presence of expression of the 15-LOX-1 transgene, expression of TNF-a and its target-inducible nitric oxide synthase was decreased and activation of NFjB in colonic epithelial cells was inhibited [41]. These results indicate that 15-LOX-1 can serve as a tumor suppressor gene.…”

“…The nuclear factor-kappa B (NF-jB) pathway is involved in the mechanistic route to IBDs such as ulcerative colitis, Crohn disease, and CAC. However, expression of 15-LOX-1 is associated with reduced expression of NF-jB, tumor necrosis factor-alpha (TNF-a), and its target, inducible nitric oxide synthase (iNOS), all of which play well-known roles in the induction of colitis [41].…”