Regulation of cell growth and expression of 7B2, PC2, and PC1/3 by TGFbeta 1 and sodium butyrate in a human pituitary cell line (HP75)

Recent studies have shown that 7B2 and the neuroendocrine-specific proconvertase PC2 have important roles in pituitary cell proliferation and hormone secretion. Studies from our laboratory have also shown that TGFb1 regulates anterior pituitary cell proliferation and hormone secretion. To study the regulation of 7B2 in human pituitary tumors, we used a cell line derived from a human pituitary adenoma (HP75) that has been shown to express 7B2, PC1, PC2, and TGFβ receptors to analyze the effects of TGFβ1 and the histone deacetylase inhibitor (HDACI) sodium butyrate (NaB) treatment on 7B2 mRNA expression along with the neuroendocrine-specific proconvertases 1/3 (PC1) and PC2 mRNA and protein expression. RNA was quantified by real-time PCR and proteins were detected by immunohistochemistry and Western blotting. Treatment of cells with 1 mM NaB or 1 nM TGFβ1 for 4 d decreased cell proliferation with a concomitant increase in the cell cycle protein p21. Real-time PCR analysis showed a significant increase in 7B2 mRNA after NaB and TGFβ1 treatment. PC2 mRNA was down regulated by NaB while PC1 mRNA was unchanged. TGFβ1 stimulated PC1, but not PC2 mRNA levels. Changes in PC1 and PC2 protein were similar to changes in the mRNAs, but the differences were not significant. These results indicated that NaB and TGFβ1 inhibit pituitary cell proliferation and regulate the expression of 7B2, PC1, and PC2 in a cell culture model of pituitary tumors. Our results also indicate that inhibition of pituitary cell proliferation is associated with increased expression of 7B2 mRNA.