Expression of chimeric human transferrin genes in vitro.

Transferrin (TF), a major plasma protein, binds and transports ferric iron. Evidence exists for unique roles for TF in brain in oligodendrocyte differentiation, myelination and neuronal development. In this study, 5' flanking regions of the TF gene important in regulating gene expression were identified by transfected cell studies and a comparison of 5' flanking sequences of the human TF and TF receptor genes. Human glioma cell lines HTB-16 and HTB-17 were shown to synthesize TF identical in size and immunological reaction to TF synthesized by liver. The expression of a series of human chimeric TF genes in glioma cells was compared with hepatoma and HeLa cells. A difference in transient expression was observed in hepatoma and glioma cells transfected with TF chimeric genes containing 3.9 kb of the 5' region; hepatoma cells demonstrated significantly more expression than did glioma cells, suggesting that a DNA region present in the 3.9-kb construct is important either in liver-specific expression or in repression of brain expression, or in both. Smaller constructs containing less than or equal to 0.622 kb of the 5' regulatory region of the TF gene failed to demonstrate cell-specific expression; they were expressed in HeLa cells, a line that does not synthesize TF. High levels of expression of 0.15-kb TF constructs were also observed in hepatoma and glioma cell lines, but not in transgenic mice. Possible explanations of differences observed in expression of shorter TF constructs in vitro and in vivo are discussed.