Transfection of the Type II TGF-β Receptor Into Colon Cancer Cells Increases Receptor Expression, Inhibits Cell Growth, and Reduces the Malignant Phenotype

Abstract

To determine if transfection of SW48 colon cancer cells with the type II transforming growth factor-beta (TGF-beta) receptor restores growth inhibition and reverses the in vitro and in vivo malignant phenotype. The authors have previously shown that SW48 colon cancer cells that are replication error positive in both alleles lack functional cell surface TGF-beta type I (RI) and type II (RII) receptors and are insensitive to TGF-beta1-induced growth inhibition. SW48 cells were stably transfected with the cDNA for the normal type II TGF-beta receptor (RII). Once transfected, the cells were evaluated for in vitro phenotypic changes and in vivo changes in tumor growth. Denaturing sequencing gel electrophoresis of the reverse transcriptase-polymerase chain reaction product from SW48 cells revealed that the RII coding sequence contained a single base deletion mutation. When these cells were transfected with normal RII cDNA, Northern and Western blot analyses revealed increased levels of RII mRNA and protein. Affinity labeling techniques revealed that RII-transfected SW48 cells produced functional RI and RII protein. Transfection of SW48 cells also led to changes in cell phenotype, as shown by inhibition of both in vitro growth rate and incorporation of [3H]-thymidine. SW48 cells expressing normal RII also exhibited reduced cloning efficiency in semisolid medium and reduced growth as a xenograft in NOD/LtSz-scid/J mice. The results confirm that RII is a tumor-suppressor protein that is required for TGF-beta-induced growth inhibition in SW48 colon cancer cells.