Expression and alternative splicing of Pit-1 messenger ribonucleic acid in pituitary adenomas

Twenty-eight human pituitary adenomas were analyzed for the expression of Pit-1 messenger ribonucleic acid (mRNA) by using reverse transcriptase-polymerase chain reaction analysis of frozen-section mRNA. Pit-1 mRNA was detected in all functioning tumors and in 9 of 11 nonfunctioning tumors. Pit-1 beta, which is a more active isoform of transcriptional factor for growth hormone than Pit- alpha and which arises from an alternative splicing mechanism, was detected in 14 of 17 functioning tumors and in 5 of 11 nonfunctioning tumors. The transcript that corresponds to Pit-1T, which increases thyroid-stimulating hormone beta promoter activity in rat thyrotropic tumor cells, was not found. There was no significant difference in the total Pit-1 (alpha+beta) mRNA expression level between functioning tumors and nonfunctioning tumors. Growth hormone-producing tumors and other pituitary adenomas also showed no significant difference in the Pit-1 beta/Pit-1 alpha expression ratio. Our data suggest that the major role of Pit-1 gene in pituitary adenoma might not be involved in the regulation of hormone production.