AUTOCRINE PRODUCTION OF TGF-ALPHA AND TGF-BETA DURING TUMOR PROGRESSION OF RAT ORAL KERATINOCYTES

This study describes a new technique to separate transforming growth f actor-alpha (TGF-alpha) and transforming growth factor-beta (TGF-beta) from culture supernatants using ion exchange chromatography; assays o f competitive inhibition of ligand binding were used to quantify the a mount of growth factor. The method was simple, inexpensive and did not require large volumes of culture medium. The autocrine production of TGF-alpha and TGF-beta was examined in oral keratinocyte cell lines de rived from the palatal and lingual mucosa of rats painted with the car cinogen 4-nitroquinoline N-oxide (4NQO). Escape from cellular senescen ce (immortality) was associated with a marked increase in TGF-alpha pr oduction (cell line R2P) but tumour progression, as reflected by the d evelopment of anchorage independence in agarose gels and tumorigenicit y in athymic mice, did not result in a consistent increase or decrease of TGF-alpha production compared to normals. Four cell lines (R8AP, R 1T, R3T, R1P), with different functional cellular phenotypes, produced two to three times more TGF-alpha than normals. TGF-alpha production was inversely correlated to epidermal growth factor cell surface recep tor expression. The autocrine production of TGF-beta was variable with the majority of cell lines producing markedly little TGF-beta; three cell lines (R4T, R8BP, R9T) produced more TGF-beta than normals. The p roduction of TGF-beta was unrelated to tumour progression, the express ion of TGF-beta cell surface receptors or TGF-alpha production. The re sults indicate that the autocrine production of TGF-alpha and TGF-beta are not accurate markers of tumour progression in the rat 4NQO model of oral carcinogenesis.