Study of pit-1 gene expression in human pituitary adenomas

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Expression of the Pit-1, its isoforms, GH,PRL and TSH beta mRNAs were studied in human pituitary adenomas (13 GH cell adenomas, 7 PRL cell adenomas, 3 TSH cell adenomas, 4 ACTH cell adenomas, and 10 clinically nonfunctioning adenomas).Pit-1 mRNA was not only expressed in normal hman and rat pituitaries, but also in all GH,PRL,and TSH cell adenomas. These was no correlation between Pit-1 transcripts and biological behavior or histological findings in these three types of adenomas, suggesting that Pit-1 is generally required for the determination of cell phenotype, but is insufficient for the regulation of hormonal activity and tumor growth in these pituitary adenomas. In addition, Pit-1 was also expressed in some ACTH cell (2/4) and nonfunctioning adenomas (7/10). Whereas there were no GH,PRL,and TSH beta transcripts in Pit-1 mRNA-negative ACTH cell and nonfunctioning adenomas, PRL mRNA was detected in all Pit-1 mRNA-positive ACTH cell adenomas and GH,PRL,and/or TSH beta mRNA were found in four of seven Pit-1 mRNA-positive nonfunctioning adenomas. In contrast, Pit-1 mRAN was expressed withot any GH,PRL,or TSH beta transcripts in only three nontunctining adenomas, indicating real Pit-1 gene expression in these nonfunctioning adenomas. These data suggest that expression of Pit-1 mRAN in these two types of adenomas can be mainly attributed to the presence of GH,PRL and/or TSH beta mRNA expressing cells and that true Pit-1 transcripts found in nonfunctioning adenomas may be a rare event. Moreover, there were two cases which expressed Pit-1 alpha mRNA,but failed to show other Pit-1 isoform mRNA.There were, however, no clinical and histological differences between these two adenomas showing only Pit-1 alpha mRNA and the others expressing both Pit-1 alpha mRNA and other Pit-1 isoform mRNA.