| Abstract: | The expression pattern of transforming growth factor-β1 (TGF-β1) during the stages of complete carcinogenesis in the hamster cheek pouch model was studied. The right cheek pouches of 18 male hamsters were treated with 0.5% 7,12-dimethylbenz[a]anthracene (DMBA) for 16 wk. TGF-β1 was detected immunohistochemically in the resulting samples with two different polyclonal monospecific antibodies that recognize intracellular and extracellular forms of TGF-β1. In the normal cheek pouch, extracellular protein stained the corium strongly, but the reaction was not evenly distributed. As treatment progressed, the reaction increased in both area and intensity; the peak was reached at 8 wk. Intracellular TGF-β1 expression followed a similar pattern, with a peak at 4 wk of treatment. The results of northern blot analysis were concordant with the immunohistochemical results. Overexpression of TGF-β1 was also observed in the malignant tumors, but only the extracellular form of the protein was present; intracellular TGF-β1 was not detected in these tumors. The expression of TGF-β1 in this carcinogenesis model seems to have two formal stages, the first being an overexpression step as a reaction to the uncontrolled growth and the second being one in which tumors have no internal expression of TGF-β1 but in which external protein accumulates in the surrounding stroma. A possible explanation of this paradox may be that TGF-β1 has functions other than its growth-repressing activity. © 1994 Wiley-Liss, Inc. |
