The pathogenesis of pituitary adenomas and many of the genes influencing growth of these tumors are unknown. TGFbeta is known to inhibit proliferation of cultured anterior pituitary cells and anterior pituitary tumors, but the signal transduction pathways involved in the inhibition of growth are unclear. We treated the human HP75 pituitary cell line with 10(-9) M TGFbeta1 for 4, 24, and 96 h and performed global gene expression profiling by Affymetrix GeneChip microarray analysis. Quantitative PCR validation of specific genes involved in the TGFbeta1-induced regulation of pituitary cell growth was also done. Of the 15,000 genes queried, there were 37 genes up-regulated and 48 genes down-regulated twofold or more after 4 h of TGFbeta1 treatment. There were 121 genes up-regulated and 109 genes down-regulated twofold or more after 24 h of TGFbeta1 treatment and 112 genes up-regulated and 43 genes down-regulated twofold or more after 96 h of TGFbeta1 treatment. Galectin-3 (Gal-3) protein was decreased by TGFbeta1 treatment and several genes which interacted with Gal-3 including RUNX1 and WNT5B were up-regulated after TGFbeta1 treatment. SOX4 was also up-regulated by TGFbeta1 treatment. SMAD3, which is directly involved in the TGFbeta signal transduction pathway, was down-regulated by TGFbeta1 treatment. These findings highlight the diverse gene networks and pathways through which TGFbeta operates in its effects on pituitary tumor cells.