The angiogenic switch in hamster buccal pouch keratinocytes is dependent on TGFbeta-1 and is unaffected by ras activation

This study was undertaken to investigate the mechanisms by which Syrianhamster buccal pouch keratinocytes treated in vivo with 7,12-dimethylbenz[a]anthracene (DMBA), switch from an angio-inhibitory to anangiogenic phenotype. Cells were cultured from pouches at various timesafter exposure to carcinogen and their angiogenic activity assessed. Theangio-inhibitory activity present in conditioned media from normal cellswas lost as early as 3 weeks after carcinogen treatment, resulting in weakexpression of angiogenic activity. By 5 weeks, cells had become stronglyangiogenic due to the secretion of high levels of TGFbeta-1, a potentangiogenic factor. Because the switch to high levels of secreted TGFbeta-1occurred at the same time as the activation of the H-ras oncogene,non-angiogenic cell lines lacking an activated H-ras oncogene were stablytransfected with mutant H-ras and their transformed and angiogenicphenotypes were evaluated. Although ras transfection drove two of the threecultured cell lines to anchorage independence and modestly increased theirability to clone in low serum, it had no effect on the angiogenic phenotypeor on the level of secreted active TGFbeta-1. These results demonstratethat the angiogenic phenotype in the hamster buccal pouch model of oralcarcinogenesis develops in a step-wise fashion with an early decrease inthe production of an inhibitor of angiogenesis and a subsequent markedincrease in the secretion of the inducer TGFbeta-1. Although the activationof the H-ras oncogene contributed to anchorage independence, it did notaffect the expression of the angiogenic phenotype in this model system.