Characterization of a pituitary-tumor-derived cell line, TtT/GF, that expresses Hoechst efflux ABC transporter subfamily G2 and stem cell antigen 1.

The anterior lobe of the pituitary gland is composed of five types of endocrine cells and of non-endocrine folliculo-stellate cells that produce various local signaling molecules. The TtT/GF cell line is derived from pituitary tumors, produces no hormones and has folliculo-stellate cell-like characteristics. The biological function of TtT/GF cells remains elusive but several properties have been postulated (support of endocrine cells, control of cell proliferation, scavenger function). Recently, we observed that TtT/GF cells have high resistance to the antibiotic G418 and low influx for Hoechst 33342, indicating the presence of ATP-binding cassette (ABC) transporters that efflux multiple drugs, i.e., a property similar to that of stem/progenitor cells. Therefore, we examine TtT/GF cells for the presence of ABC transporters, for the efflux ability of Hoechst 33342 and for those genes characteristic of TtT/GF cells. Real-time polymerase chain reaction (PCR) for ABC transporters demonstrated that Abcb1a, Abcb1b and Abcg2, regarded as stem cell markers, were characteristically expressed in TtT/GF cells but not in Tpit/F1 and LβT2 cells. Furthermore, the remarkable low-efflux ability of Hoechst 33342 from TtT/GF cells was confirmed by using inhibitors and contrasted with the abilities of Tpit/F1 and LβT2 cells. The high and specific expression of stem cell antigen 1 (Sca1) in TtT/GF cells was confirmed by real-time PCR. We also demonstrated those genes that are expressed abundantly and characteristically in TtT/GF, suggesting that TtT/GF cells have unique characteristics similar to those of stem/progenitor cells of endothelial or mesenchymal origin. Thus, the present study has revealed an intriguing property of TtT/GF cells, providing a new clue for an understanding of the function of this cell line.