CD44H Participates in the Intrahepatic Growth of Murine Colon 26 Adenocarcinoma Cells

The purpose of this study was to determine if CD44, a metastasis‐associated cell adhesion molecule, is involved in the hepatic colonization by murine colon 26 adenocarcinoma cells. Indirect membrane immunofluorescence and FACS analysis showed strong expressions of CD44 and integrin β(1) on colon 26 cells. Injection of 1×10(5) colon 26 cells into the superior mesenteric vein of syngeneic BALB/c mice produced macroscopic hepatic nodules in 92% (22/24) of the mice 14 days after inoculation. When colon 26 cells were pretreated with an anti‐CD44 monoclonal antibody (mAb), IM7, only 30% (3/10) of the mice produced minute nodules in the liver on day 14 (P<0.001), though IM7 did not inhibit growth of the cells in vitro. Pretreatment of colon 26 cells with an anti‐integrin β(1) mAb did not significantly block the hepatic metastasis. Histologically, microcolonies of tumor cells were detected in all of the livers on day 14 including the IM7‐pretreatment mice that were free of gross nodules. However, percentages of tumor‐occupied areas in the liver were consistently lower in IM7‐pretreatment mice than in control mice (0.82% vs. 5.0% on day 14; P<0.005). Reverse transcription‐polymerase chain reaction (RT‐PCR) amplification of mRNA revealed that colon 26 cells and splenocytes only expressed the hematopoietic isoform of CD44 (CD44H), which had no insertion of variant exons, while normal colonocytes expressed possible variant isoforms. These data suggest that malignant transformation of murine colonic epithelium altered the expression pattern of CD44 isoforms and that CD44H participates in the intrahepatic growth of colon 26 cells.