7. Dkk‐1/Ror2 and Wnt5a/Ror2 Production of CDX2: Defining Intestinal Adenocarcinoma

Abstract

Wnt signaling regulates cell proliferation and differentiation through ahomeostasis of canonical and noncanonical pathways. Aberrant Wnt signaling induces intestinal adenocarcinoma by promoting stem cell hyperproliferation. In the intestine, Wnt5a binds to its receptor Ror2 to increase the caudal homeobox factor CDX2, a transcriptional activator of intestinal differentiation. Contradictorily, it was also shown that Ror2 alone is overexpressed in adenocarcinoma, and that Ror2 alone will mediate CDX2 increase in vitro. The purpose of this research is to determine how CDX2 is increased by Ror2 alone and Wnt5a/Ror2. Human colon adenocarcinoma cells (HT‐29, SW‐480, and RKO) were used as an in vitro epithelial model. HT‐29 cells constitutively express the signaling protein Dickkopf‐1, whereas SW‐480 and RKO do not. Wnt5a/rhDkk‐1 was used to treat Ror2 or siRor2 transfected cells primed with MAP kinase pharmacological inhibitors. The results show that CDX2 was increased after Ror2 overexpression in HT29, but not RKO/SW480 cells. Further addition of Dkk‐1 to RKO/SW480 cells resulted in CDX2 increase. Pharmacological inhibition of p38 MAPK, casein kinase 1, or Src kinase decreased CDX2 protein ~24% in Dkk‐1/Ror2 cells, while inhibition of JNK, casein kinase 1, or Src kinase in Wnt5a/Ror2 cells decreased CDX2 protein ~35%. The conclusion is that Ror2 increase in CDX2 protein is dependent on Dkk‐1 or Wnt5a. Dkk‐1/Ror2 CDX2 production is mediated by the MAP kinases p38, CK1, and Src. Wnt5a/Ror2 increases in CDX2 require JNK activation, but not p38 MAPK. Different signaling pathways, dependent on the presence of Dkk1/Wnt5a, offer an explanation for the seemingly contradictory increase in Ror2 alone seen in intestinal adenocarcinoma.