The angiogenic switch in hamster buccal pouch keratinocytes is dependent on TGFbeta-1 and is unaffected by ras activation |
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Authors: | Lingen MW; DiPietro LA; Solt DB; Bouck NP; Polverini PJ |
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Institution: | Northwestern University Medical School, Department of Pathology, Chicago, IL 60611, USA. |
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Abstract: | This study was undertaken to investigate the mechanisms by which Syrian
hamster buccal pouch keratinocytes treated in vivo with 7,12-
dimethylbenza]anthracene (DMBA), switch from an angio-inhibitory to an
angiogenic phenotype. Cells were cultured from pouches at various times
after exposure to carcinogen and their angiogenic activity assessed. The
angio-inhibitory activity present in conditioned media from normal cells
was lost as early as 3 weeks after carcinogen treatment, resulting in weak
expression of angiogenic activity. By 5 weeks, cells had become strongly
angiogenic due to the secretion of high levels of TGFbeta-1, a potent
angiogenic factor. Because the switch to high levels of secreted TGFbeta-1
occurred at the same time as the activation of the H-ras oncogene,
non-angiogenic cell lines lacking an activated H-ras oncogene were stably
transfected with mutant H-ras and their transformed and angiogenic
phenotypes were evaluated. Although ras transfection drove two of the three
cultured cell lines to anchorage independence and modestly increased their
ability to clone in low serum, it had no effect on the angiogenic phenotype
or on the level of secreted active TGFbeta-1. These results demonstrate
that the angiogenic phenotype in the hamster buccal pouch model of oral
carcinogenesis develops in a step-wise fashion with an early decrease in
the production of an inhibitor of angiogenesis and a subsequent marked
increase in the secretion of the inducer TGFbeta-1. Although the activation
of the H-ras oncogene contributed to anchorage independence, it did not
affect the expression of the angiogenic phenotype in this model system.
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