Akira Teramoto

Mutations of the MEN1 tumor suppressor gene in sporadic pituitary tumors

Pituitary adenoma is a common neoplasm accounting for 10% of all intracranial tumors. Although the molecular mechanisms underlying the formation of these tumors are largely unknown, a small portion of pituitary adenomas occur in patients with the multiple endocrine neoplasia syndrome type 1 (MEN 1). Although two groups in the United States and Canada have recently reported that sporadic pituitary adenomas very rarely harbor a somatic mutation in the MEN1, MEN1 gene mutation analysis in sporadic pituitary adenomas has not yet been carried out in the Japanese population. To elucidate the potential etiological role of the MEN1 gene in the formation of sporadic pituitary adenomas in Japan, we investigated 40 Japanese patients with sporadic pituitary adenomas (16 hormone-secreting and 24 nonsecreting tumors) for MEN1 gene mutation. Polymerase chain reaction-single-stranded DNA conformation polymorphism analysis and sequencing demonstrated a somatic mutation in the MEN1 gene in only one of the 40 tumors, a prolactinoma, which had a 1-bp deletion in the coding sequence of exon 2. The data suggest that somatic mutations in the MEN1 gene do not play a prominent role in the pathogenesis of sporadic pituitary adenomas.

Expression of Ptx1 in the adult rat pituitary glands and pituitary cell lines: hormone-secreting cells and folliculo-stellate cells.

Abstractu2002The pituitary homeobox1 gene (Ptx1) was initially identified as encoding a pituitary-restricted transcription factor for the proopiomelanocortin (POMC) gene. In order to elucidate the expression pattern of the Ptx1 protein, we investigated the localization of the protein in adult rat pituitary gland and in various pituitary cell lines. We produced an antibody specific for Ptx1 protein, and confirmed its specificity by Western blot analysis. Immunohistochemically, many nuclei in the anterior pituitary cells as well as in the intermediate cells were positive for Ptx1 staining with this specific antibody. Immunohistochemical double staining revealed the presence of Ptx1 not only in all types of hormone-secreting cells but also in some folliculo-stellate (FS) cells. Furthermore, the expression of Ptx1 mRNA was confirmed in various pituitary cell lines and in the FS cell line by using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Our studies indicated that Ptx1 may not only play a role as a basic transcriptional factor for production of various hormones, but may also play some important role(s) in FS cells. Possible synergistic actions with other factors remain to be investigated. The novel finding of Ptx1 in FS cells is of particular interest, and may suggest that FS cells and hormone-secreting cells are derived from a common cellular ancestor.

Expression of Pit-1 mRNA and Activin/Inhibin Subunits in Clinically Nonfunctioning Pituitary Adenomas

The pituitary-specific transcriptional factor Pit-1 is known to play a role in the development and differentiation of pituitary cells. Recent investigations have suggested a role for this transcriptional factor in pituitary adenomas, especially growth hormone (GH)- and prolactin (PRL)-secreting pituitary adenomas. In this study we analyzed the expression of Pit-1 mRNA and its protein in 24 clinically nonfunctioning pituitary adenomas in comparison with normal pituitary glands using in situ hybridization (ISH) and immunohistochemistry (IHC). The interaction between inhibin/activin, a member of the transforming growth factor-β family, and Pit-1 was also studied. Immunohistochemically, Pit-1 protein was detected in 9 of 24 adenomas (37.5%), and 8 of these 9 were also positive for the α subunit of glycoprotein (αSU). The expression of Pit-1 mRNA was detected in 14 of 24 (58.3%) clinically nonfunctioning adenomas, and it was found in all cases which expressed the Pit-1 protein. By the combined ISH and IHC method, Pit-1 mRNA was frequently observed in αSU-immunopositive cells in adenomas. The inhibin/activin α subunit was detected in all 24 adenomas and the βA subunit was detected in 13 of 24 adenomas. The inhibin/activin βA subunit was detected frequently with Pit-1 mRNA. From our observations, the inhibin/activin βA subunit in nonfunctioning adenomas may have related the expression of Pit-1 mRNA in these adenomas.

Analysis of the MEN1 gene in sporadic pituitary adenomas from Japanese patients

An autosomal-dominant syndrome known as multiple endocrine neoplasia type 1 (MEN1) is characterized by tumors in parathyroid glands, pancreatic endocrine tissues and the anterior pituitary gland. The predisposing gene was identified at 11q13 when germline mutations in the MEN1 gene were detected in affected pedigrees. To investigate a possible role of this gene in tumorigenesis of non-familial pituitary adenomas, we examined 24 sporadic tumors from Japanese patients for loss of heterozygosity (LOH) at the 11q13 region and for somatic mutations in the entire coding region and exon-intron boundaries of MEN1. Although three common sequence variants were detected, none of the tumors exhibited either LOH or somatic mutations of this gene. Our results indicate that inherited and sporadic forms of pituitary adenomas are different in terms of the genetic events that contribute to their development, and that other loci associated with pituitary neoplasia must still be sought.

Retinoid X receptors (RXRs) mRNA expression in human pituitary adenomas

Retinoid-X receptors (RXRs) are transcriptional factors that belong to the steroid/thyroid hormone receptor (TR) superfamily. It has been demonstrated that those nuclear receptors act as ligand-activated transcription factors in pituitary cells. To determine whether RXRs play roles in the cell differentiation of pituitary adenomas, we have investigated the expression of RXRγ mRNA in various types of pituitary adenomas usingin situ reverse transcriptase-polymerase chain reaction (RT-PCR). The synergistic function on promoters of specific hormones between these nuclear receptors and pituitary specific transcription factor, Pit-1, has been noticed in in vitro experiments. The colocalization between RXRγ mRNA and Pit-1 protein was examined by combinedin situ RT-PCR and immunohistochemistry. RXRγ mRNA was detected in normal pituitary gland as well as all five growth hormone-(GH)-secreting adenomas and five thyroid stimulating hormone (TSH) secreting adenomas, two of four prolactin- (PRL) secreting adenomas, one of two adrenocorticotropin-(ACTH) secreting adenomas, one of four nonfunctioning adenomas. Byin situ hybridization andin situ RT-PCR followed by immunohistochemistry, the colocalization of Pit-1 mRNA with RXRγ as well as RXRγ mRNA with Pit-1 was observed in adenoma cells of GH-secreting adenomas and TSH-secreting adenomas. We suggest that RXRγ may play a role in cell differentiation and hormonal transcription synergistically with Pit-1 in normal and neoplastic human pituitaries.