THYROTROPIN (TSH) BETA-SUBUNIT GENE-EXPRESSION - AN EXAMPLE FOR THE COMPLEX REGULATION OF PITUITARY-HORMONE GENES

Synthesis of pituitary hormones was shown to be efficiently regulated at the transcriptional level. The specialized function of the five cel l types in the anterior pituitary is controlled by ubiquitous as well as cell-specific transcription factors. Pit-1 is such a cell-specific regulator found only in lacto-, somato-and thyrotropes which could be shown to be essential for basal expression of growth hormone (GH) and prolactin (Prl) genes and the regulated expression of Prl and thyrotro pin (TSH) beta-subunit genes. Identification of distinct binding sites for transcription factors and some of the mechanisms of transcription al control shed light on the complex regulation of pituitary hormone g ene expression which is exemplified for the TSH beta gene. The control of basal as well as positively and negatively regulated expression of some pituitary hormone genes becomes fairly well understood by the in vestigation of the role of Pit-1. Identification of different mutation s in the human pit-1 gene supported the role of this protein for combi ned pituitary hormone deficiency (CPHD) characterized by the deficienc y of GH, prolactin and TSH.