A human pituitary adenoma cell line proliferates and maintains some differentiated functions following expression of SV40 large T-antigen

Human pituitary cells proliferate very slowly in vitro. Only a few cell lines have been established, and these have been used mainly for short-term studies. To obtain immortalized cell lines of human pituitary adenomas for in vitro studies, we infected adenoma cells with a replication-defective recombinant human adenovirus, which contains an SV40 early large T-antigen. One of the cell lines (HP75), which has been studied in culture during 60 passages, has been extensively characterized. It expressed the large T- antigen protein and its mRNA, as well as the genes for FSH-β, LH-β and α- subunit (α-SU) of gonadotropin hormone. The HP75 cell line also expressed the genes of various members of the chromogranin (Cg)/secretogranin (Sg) family, including CgA as well as the prohormone convertases PC1/3 and PC2. CgA was processed to pancreastatin in vitro, which was secreted into the culture medium. Treatment with phorbol 12-myristate 13-acetate (PMA), TGF- β1, and forskolin increased CgA expression in the cells and stimulated pancreastatin secretion into the medium while inhibiting cell growth. The HP75 cell line also expressed TGF-β mRNA isoforms (β1, β2, b3) and the mRNAs for the receptors for TGF-β (RI, RII, and RIII). The cells responded to TGF-β1 in vitro by increasing CgA protein expression and pancreastatin secretion. TGF-β-RII protein and mRNA expression were both increased by PMA. Ultrastructural studies showed that the HP75 cells had very few dense-core secretory granules and a poorly developed Golgi complex. After treatment with TGF-β1 and PMA, there was an increase in the development of rough endoplasmic reticulum and the Golgi complex. This is the first report of the development of an immortalized human pituitary cell line that retains some differentiated functions. HP75 can be used to study TGF-β and CgA functions in pituitary cells. Replication-defective recombinant human adenovirus with an SV40 large T-antigen insert can be used to generate other immortalized human pituitary cell lines for in vitro studies.