Our data that claudin-2 expression decreases sharply in differentiating colonocytes and/or CRC cells, and claudin-2 expression positively affects cell growth while inhibiting P-21 expression suggests that the increased claudin-2 expression in CRC cells may help promote colon tumorigenesis by facilitating dedifferentiation and cell cycle progression. The gene discussed is CLDN2; the disease is colorectal carcinoma.