Colorectal cancer is the third leading cause of cancer deaths in the United States. The long-term goal of our
research is to develop novel interventions to prevent colorectal carcinogenesis (CRC). CRC invasiveness, a
critical adverse step during CRC progression, requires a combination of certain genetic mutations (e.g. APC,
KRAS and Trp53 mutations), which are the key events to drive CRC. However, CRC progression also requires
additional factors which increase aberrant Beta-catenin (B-catenin) activation above levels induced by APC/B-
catenin mutations. Linoleic acid (LA), the most commonly consumed omega-6 polyunsaturated fatty acids in
humans, increases both chemically (AOM)– and APC mutation– induced CRC tumorigenesis in mice.
Nonetheless, human studies have been inconclusive regarding the impact of dietary LA on CRC. Determination
of LA's role in CRC is important because American diets are enriched with LA while expression of the main
metabolizing enzyme for LA,15-lipoxygenase-1 (ALOX15), is lost in human CRC. Recently, we found that 1)
high dietary levels of LA promoted CRC by increasing phosphatidylinositol 3-phosphate (PI3P) containing LA
(PI3P_LA), which increases LRP5 membranous recycling and subsequently B-catenin activation; 2) ALOX15-
induced conversion of PI3P_LA to PI3P_13-HODE suppresses; LRP5 membranous recycling, B-catenin
activation, CRC stemness and LA promotion of CRC, especially formation of large tumors, associated with CRC
invasiveness; 3) ALOX15 loss of function (LOF) promotes large CRC tumor formation by azoxymethane in
12/15LOX-KO-12LOX (ALOX15-LOF) mice. Whether loss of ALOX15 expression promotes CRC invasiveness
remains unknown. Our preliminary data show that ALOX15-LOF mice increased CRC invasiveness and targeted
APC mutation into Lgr5+ colorectal stem cells induced CRC in the mice, which was blocked by transgenic
ALOX15 expression. We therefore hypothesize that ALOX15 loss of function promotes CRC invasiveness by
increasing PI3P_LA levels, which enhances LRP5 membranous recycling, thus potentiating Wnt/B-catenin
signaling and subsequently stemness. Aim 1 will determine the effects of ALOX15 gain of function and ALOX15
LOF on LRP5, B-catenin activation, CRC stemness and invasiveness using CRC mouse models in which CRC
invasiveness is promoted by either a combination of APC, KRASG12D and Trp53R172H mutations or Trp53R172H
mutation with AOM induced B-catenin and KRAS mutations. Aim 2 will determine the effects of ALOX15 LOF
on PI3P-LA, LRP5, B-catenin activation, stemness and invasiveness in human CRCs and examine the effects
of ALOX15 re-expression via lentivirus Tet-on inducible system in human CRC-derived organoids on
invasiveness in-vitro and in-vivo studies. The proposed studies are expected to provide important mechanistic
insights into whether colonic ALOX15 expression as a host factor affects CRC invasiveness risk especially with
high dietary LA intake. This gained knowledge could inform subjects with colorectal ALOX15 LOF to avoid high
LA intake and spur development of interventions to target ALOX15 for re-expression to prevent invasive CRC.