The Tumor Endocrinology Project aims at the development of new tools for tumor prevention, diagnosis and treatment by elucidating the effects of endocrine environment on carcinogenesis, as well as the effects of tumor-derived substances on the pathophysiology in the patients. The role of tumor-associated transcription factors in tumorigenesis and the transcriptional control of T lymphocyte functions are currently being studied. Our research has also focused on the oncogenic mechanism of the development of endocrine tumors. In relation to the study of hereditary endocrine tumors, new diagnostic tests for familial cancer syndromes are being developed.

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome characterized by the occurrence of multiple tumors in various endocrine tissues, including the pituitary, parathyroid, and enteropancreatic endocrine tissues. Elucidation of the functions of menin, the protein product of the causative gene MEN1, will lead to a better understanding of the oncogenic mechanism common to the development of variety of endocrine tumors.

In collaboration with many hospitals, germline and somatic mutations of the MEN1 gene have been explored in patients with MEN1 and related disorders. Although various pathogenic germline mutations have been detected in almost all MEN1 patients, routine PCR-based sequencing analysis has occasionally failed to identify the mutations responsible for MEN1. These mutation-negative MENs were shown to be caused by a heterozygous deletion of the whole MEN1 gene that escaped detection during routine screening. An analytical method exploiting the principle of quantitative PCR was developed in order to detect large germline deletions efficiently. This method was demonstrated to be useful for DNA diagnosis of not only MEN1 but also other familial cancer syndromes, including hereditary retinoblastoma and familial adenomatous polyposis. A similar but even more rapid method for the detection of deletion is now being developed.

Several missense mutations have been shown to be associated with a subset of familial isolated hyperparathyroidism. Germline missense mutations were also found in patients with apparently sporadic parathyroid tumors. Such mutation-positive hyperparathyroidism should be regarded as a mild form of MEN1 and genetic counseling and long-term follow-up for recurrence are necessary after tumor resection. However, because many missense mutations of the MEN1 gene also cause typical MEN1, it is difficult to determine whether the novel missense mutation identified in the proband exhibiting only hyperparathyroidism could cause typical MEN1 or only milder forms, unless the proband has a positive family history of MEN1. Missense menin mutants causative of typical MEN1 were shown to degrade more rapidly than wild-type menin in culture cells. A diagnostic test for predicting the prognosis of missense mutant carriers is now being developed on the basis of the intracellular instability of mutant menin proteins.

NOR1 is a nuclear receptor-type transcription factor in the steroid receptor superfamily, and is thought to be involved in the development of the immune and nervous systems. In extraskeletal myxoid chondrosarcoma, the NOR1 gene is frequently fused to the EWS gene by chromosomal translocation t(9;22), and the resulting chimeric gene generates the EWS/NOR1 fusion protein. It has been speculated that the tumor development may be attributable to EWS/NOR1-induced irrelevant expression of the genes that are normally activated by NOR1. However, comprehensive expression analysis with DNA chips revealed wide differences between the NOR1-induced and EWS/NOR1-induced gene groups, indicating that the target genes of EWS/NOR1 are different from those of NOR1. These findings suggest that tumorigenesis by the EWS/NOR1 fusion protein may not be triggered by the simple activation of NOR1 target genes. The mechanisms of differential gene induction by these transcription factors are now being investigated.

Regulatory T cells (Tregs) are engaged in the maintenance of immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. Because experimental depletion of Tregs has been shown to induce or enhance antitumor immunity, manipulation of Treg numbers and their function may become a new therapeutic modality for human tumors as well as for autoimmune diseases, allergy, and transplantation rejection. Recently, the transcription factor Foxp3 was identified as a master regulator of Treg differentiation. Ectopic expression of Foxp3 in conventional T cells is known to be sufficient to confer suppressive activity, repress the production of cytokines, such as IL-2 and interferon-gamma, and upregulate Treg-associated molecules such as CD25, cytotoxic T-lymphocyte-associated antigen-4, and the glucocorticoid-induced TNF-receptor-family- related protein. However, the mechanism by which Foxp3 controls these molecular events has yet to be explained.

In order to clarify the role of Foxp3 in the Treg functions, the mechanism of IL-2 gene repression by Foxp3 has been investigated ⁽¹⁵⁵⁾. Foxp3 and AML1 have been demonstrated to bind to the IL-2 gene promoter and repress and enhance IL-2 gene expression, respectively. Foxp3 has been shown to interact physically with AML1 in Tregs. This interaction resulted in the transcriptional repression of not only IL-2, but also of interferon-gamma, and upregulation of Treg-associated molecules, thereby mediating the immunosuppressive activity of Treg. This regulatory mechanism of Treg function through the interaction between Foxp3 and AML1 might be exploited as a therapeutic target in the treatment of immune diseases and cancer.