Ceacam1 also directly regulates intestinal epithelia. Due to enhanced Wnt/b-catenin signaling, Ceacam1 2/2 jejunal and ileal enterocytes exhibit higher levels of the positive cell cycle regulators c-Myc and cyclin D1 [41] . Dysregulated c-Myc may sensitize cells to apoptosis [42, 43] , and higher levels of these proteins may render Ceacam1 2/2 enterocytes more sensitive to radiation injury. Finally, Ceacam1 also regulates cell-cell adhesion [17, 18, 44, 45] under normal and pathological conditions; it may therefore also be possible that loss of Ceacam1 regulates radiationinduced sloughing of intestinal epithelium.