Autocrine production of TGF-α and TGF-β during tumour progression of rat oral keratinocytes

This study describes a new technique to separate transforming growth factor-α (TGF-α) and transforming growth factor-β (TGF-β) from culture supernatants using ion exchange chromatography; assays of competitive inhibition of ligand binding were used to quantify the amount of growth factor. The method was simple, inexpensive and did not require large volumes of culture medium. The autocrine production of TGF-α and TGF-β was examined in oral keratinocyte cell lines derived from the palatal and lingual mucosa of rats painted with the carcinogen 4-nitroquinoline N-oxide (4NQO). Escape from cellular senescence (immortality) was associated with a marked increase in TGF-α production (cell line R2P) but tumour progression, as reflected by the development of anchorage independence in agarose gels and tumorigenicity in athymic mice, did not result in a consistent increase or decrease of TGF-α production compared to normals. Four cell lines(R8AP, R1T, R3T, R1P), with different functional cellular phenotypes, produced two to three times more TGF-α than normals. TGF-α production was inversely correlated to epidermal growth factor cell surface receptor expression. The autocrine production of TGF-β was variable with the majority of cell lines producing markedly little TGF-β three cell lines (R4T, R8BP, R9T) produced more TGF-β than normals. The production of TGF-β was unrelated to tumour progression, the expression of TGF-β cell surface receptors or TGF-α production. The results indicate that the autocrine production of TGF-α and TGF-β are not accurate markers of tumour progression in the rat 4NQO model of oral carcinogenesis.