Inhibition of Head and Neck Squamous Cell Carcinoma Cell Lines by Transforming Growth Factor-β

Abstract

Transforming growth factor-β is known to be a potent autocrine growth inhibitor produced by a wide variety of cells, including cells of the immune system. Other investigators have noted that the growth of nontransformed keratinocytes is inhibited by transforming growth factor-β, whereas various carcinoma cell lines are resistant to these effects. Head and neck squamous cell carcinoma cells are known to have surface receptors for this cytokine. We thus assessed the effect of transforming growth factor-β on the growth of head and neck squamous cell carcinoma cell lines. Four head and neck squamous cell carcinoma cell lines were incubated with varying concentrations of transforming growth factor-β, and cytotoxicity was evaluated with a methylene blue colorimetric assay. After culturing in transforming growth factor-β for 4 days, inhibition of growth was detected in CAL-27 (maximal inhibition at 5.0 ng/ml), UMSCC-1, and UMSCC-19 (maximal inhibition at 50 ng/ml) cell lines. One other cell line, UMSCC-8 was found resistant to the inhibitory effects of transforming growth factor-β. Kinetics analysis experiments revealed minimal inhibition before day 2 of incubation, at which time inhibition increased linearly to day 4. Assessment of double-stranded DNA fragmentation suggested that DNA fragmentation occurs before significant cytotoxicity. Electron microscopic analysis and gel electrophoresis of extracted DNA revealed morphologic features consistent with apoptotic cell death. Our findings indicate that transforming growth factor-β significantly inhibits the growth of head and neck squamous cell carcinoma cell lines by inducing apoptotic cell death.