Endogenous TGF-beta 1 inhibits the growth and metastatic dissemination of rat oral carcinoma cell lines but enhances local bone resorption

This study examined the effect of stable transfection of latent transformin g growth factor-beta 1 (TGF-beta 1) cDNA into a predominantly polygonal, 4 nitroquinoline N-oxide (4NQO)-induced rat oral keratinocyte cell line. Seve n polygonal and five spindle clonal populations were isolated that overexpr essed TGF-beta 1 protein by approximately two- to four-fold compared to vec tor-only transfected controls. Neutralisation experiments indicated that th e majority of protein was in the latent form. There was no change in the pr oportion of polygonal and spindle cells in vitro after transfection with TG F-beta 1 cDNA. Polygonal and spindle cells that overexpressed TGF-beta 1 pr oduced similar amounts of protein and grew more slowly in vitro than contro ls. The parent cell line and all transfected cells were growth inhibited (6 0-75%) by exogenous TGF-beta 1. Orthotopic transplantation of the parent an d the vector-only control cell lines resulted in primary tumours in the flo or of the mouth in almost 100% (20/21) of athymic mice, with no evidence of bone resorption at the site of the primary tumour and pulmonary metastatic tumour deposits in some 40% (7/20) of these animals. The polygonal and spi ndle cells that overexpressed TGF-beta 1 behaved similarly following orthot opic transplantation. A 96% (23/24) primary tumour take was evident followi ng transplantation of cells that overexpressed TGF-beta 1, with a significa ntly (P<0.02) higher number of animals showing bone resorption at the site of the primary tumour (35%; 8/23) compared to controls. By contrast, there was a significant (P<0.03) decrease in the number of animals with pulmonary metastases (4%; 1/23) following transplantation of TGF-beta 1 overexpressi ng cells compared to controls. Overexpression of TGF-beta 1 did not alter t umour cell differentiation in vivo. The results demonstrate that endogenous TGF-beta 1 functions as a tumour suppressor in the rat-4NQO model of oral carcinogenesis without altering tumour cell morphology or differentiation b ut can also act to promote local bone resorption.