ANTISENSE TO CYCLIN D1 INHIBITS THE GROWTH AND TUMORIGENICITY OF HUMAN COLON-CANCER CELLS

Cyclin D1 plays an important role in regulating the progression of cel ls through the G1 phase of the cell cycle. This gene is frequently ove r-expressed in human colon cancer. To address the role of cyclin D1 in growth control and tumorigenesis in this disease, we have overexpress ed an antisense cyclin D1 cDNA construct in the human colon cancer cel l line SW480E8, which expresses high levels of cyclin D1. The integrat ion and expression of the antisense construct was verified by Southern and Northern blot analyses, respectively, and resulted in decreased e xpression of the cyclin D1 protein. This was associated with decreased levels of the Rb and p27(Kip1) proteins. In addition, the hypophospho rylated form of Rb was increased in these cells. The SW480E8 antisense cyclin D1 cells displayed an increased doubling time, a decrease in s aturation density, decreased plating efficiency and anchorage-independ ent growth, and a loss of tumorigenicity in nude mice. These findings provide direct evidence that increased expression of cyclin D1 in colo n tumor cells contributes to their abnormal growth and tumorigenicity. The ability to revert the transformed phenotype of these cells with a ntisense cyclin D1 suggests that cyclin D1 or its associated cyclin-de pendent kinase 4 may be useful targets in the therapy of colon cancer.