Oestrogen receptor independent expression of progestin receptors in human meningioma--a review.

Human meningiomas are rich in progestin receptors (PR), which are expressed in this tissue in an oestrogen independent fashion. In the search for an explanation of this observation, the existence of a protein in human meningioma cytosol which is capable of binding to a synthetic oestrogen responsive element (ERE) has been demonstrated. Using reverse transcriptase, PCR mRNA encoding for the wild-type oestrogen receptor (ER) was found. In addition, several splice variants of ER mRNA have been identified in human meningioma tissue, including variants lacking exons 4, 5 and 7. We found the ER delta 4 protein to have no transcriptional activity and the ER delta 7 protein reportedly is dominant negative. These mutants therefore probably are not responsible for the autonomous PR synthesis in human meningioma. The ER delta 5 protein, by contrast, has been reported to have oestrogen independent transcriptional activity and it is tempting to speculate that this protein is similar or identical to the ERE binding protein we have found in human meningioma. The role of wild type ER mRNA is presently unclear. Activation of other signal transduction pathways in meningioma does not lead to an increased PR concentration. The promoter area of the meningioma PR gene should be investigated for the possible sensitivity to other transcription factors.