Purpose: Adhesion of tumor cells to endothelial cells and to the extracellular matrix is a key step in the initial phase of metastasis. Since radiotherapy of tumors can induce alterations of the cell surface, we investigated the effect of ionizing radiation on the expression of integrins in the colorectal tumor cell line COLO-320 and the modulation of adhesion capacity of irradiated cells to collagen and fibronectin.
Material and methods: The cell surface expression of a broad range of integrins on COLO-320 cells was determined by flow cytometry during 144 hours after X-irradiation. The functional significance of increased adhesion molecule expression was assessed by cell-matrix adhesion and receptor blocking experiments.
Results: Cell surface expression of the following integrin alpha and beta subunits was quantified: beta1 (CD29), alpha 2 (CD49b), alpha 5 (CD49e) and alpha 6 (CD49f). The expression of alpha 1, alpha 2, alpha 5, and alpha 6 changes as a function of time after irradiation (5 Gy). For beta1 even a function of dose (1-5 Gy) could be shown. Adhesion experiments confirmed a time dependent increase in adhesion to both collagen and fibronectin. Radiation-induced increase in adhesion was inhibited significantly by using a CD29 antibody.
Conclusions: Ionizing radiation modulates cell surface expression of integrins and cell-matrix interactions. The beta1-integrin subunit plays an important role in radiation-induced adhesion to both collagen and fibronectin. Possible consequences of these in-vitro results for radiotherapy of colorectal tumors in vivo are discussed.