September 07, 2023

Discovery of Novel Cancer Signaling Axis Characterizing Hepatocellular Carcinoma
(Prof.A.Kikuchi, in Oncogene)

Overview of the Research

Specially Appointed Professor Akira Kikuchi, Center for Infectious Diseases Education and Research, Osaka University, and Assistant Professor Koei Shinzawa, Graduate School of Medicine, Osaka University, have identified a novel cancer signaling axis and molecular target for treatment in malignant melanoma.

Malignant melanoma is a type of skin cancer that originates from melanocytes or nevi, causing about 80% of skin cancer-related deaths. It occurs more frequently in the skin of Caucasian individuals exposed to ultraviolet radiation from sunlight, and somatic mutations in genes such as BRAF and NRAS have been observed. While some cases have shown significant response to BRAF inhibitors, as well as antibodies against CTLA-4 and PD-1 (immune checkpoint inhibitors), there are also cases in which these treatments have proven ineffective. Therefore, the development of new therapeutic agents for the cases resistant to these drug therapies has been required.

GREB1 is a nuclear protein that functions as a co-regulator for hormone receptors, enhancing their transcriptional activity. As it is induced by hormone receptors, it forms a positive feedback loop. GREB1 has been found to be upregulated in hormone-dependent cancers, including breast and prostate cancers, promoting the proliferation of these cancer cells. Although the association of GREB1 with hormone-independent cancers has been unclear so far, the research group had reported high expression of GREB1 in hepatoblastoma and hepatocellular carcinoma, promoting the proliferation of these cancer cells. In this study, the research group discovered that the expression of a specific isoform of GREB1 (Isoform 4, Is4) is induced in malignant melanoma cells under the influence of the melanocyte-specific transcription factor, MITF. They revealed that GREB1 Is4 promotes cancer cell proliferation through the regulation of pyrimidine metabolism. Furthermore, the anti-tumor effect of antisense nucleic acids against GREB1 showed a potential new modality for malignant melanoma.

In conclusion, these findings shed light on a promising molecular target for the treatment of malignant melanoma, potentially leading to the development of more effective therapies for cases that do not respond to current treatment options. This study was published in Oncogene on 1 September, 2023.


Schematic representation of this study

License: Original content

Credit: Koei Shinzawa

Background of the Study

Melanoma is a malignant tumor caused by the cancerous transformation of melanocytes. The incidence of melanoma is high in Caucasians, but it affects 1 to 2 per 100,000 Japanese, and approximately 1,800 people are diagnosed with malignant melanoma per year in Japan. There are differences in response to immune checkpoint inhibitors by melanoma type, with low response rates in the acral and mucosal melanoma types, which are common among Japanese, while molecular targeted therapies (BRAF and MEK inhibitors) can prolong survival and achieve high response rates, but the incidence of drug resistance is a problem. About 30% of melanomas develop from pigmented nevi, and it has not been fully elucidated which genes are expressed in the neoplastic stage and how they become melanoma. The research group focused on the GREB1 Is4 gene, of which expression is induced by MITF, a pigment cell-specific transcription factor that produces pigments in melanocytes, to analyze its new role in cancer development and its potential as a new therapeutic target.

Research Achievements

1.The research group found that GREB1 Is4, which encodes only the C-terminal half of full-length GREB1, is specifically expressed in malignant melanoma, and its expression is induced by MITF in collaboration with Department of Genome Biology at Osaka University Graduate School of Medicine.

2.The research group found that MITF and GREB1 are co-expressed in tissues of benign nevi and malignant melanoma, and that MITF and GREB1 expression is particularly high in malignant melanoma with melanoma thickness and poor prognosis in collaboration with Departments of Dermatology at Osaka University Graduate School of Medicine.

3.In collaboration with Research Institute for Microbial Diseases at Osaka University, the research group generated GREB Is4 transgenic mice and showed that induction of GREB Is4 expression promotes tumor development in BRAF (V600E mutation) and PTEN loss malignant melanoma model mice.

4.As a binding protein of GREB1 Is4, the research group identified Carbamoyl-phosphate synthetase 2, Aspartate transcarbamylase, and Dihydroorotase (CAD), the rate-limiting enzyme for pyrimidine synthesis, and showed biochemically that GREB1 Is4 promotes the activation of CAD. Furthermore, in collaboration with the Institute for Advanced Biosciences at Keio University, they showed by metabolomic analysis that GREB1 Is4 is required for efficient pyrimidine synthesis in malignant melanoma.

5. The research group generated a xenograft mouse model implanted with human melanoma and showed that antisense oligonucleic acid against GREB1 reduced tumor size.

Significance of the Research Findings

While immune checkpoint inhibitors have dramatically advanced the treatment of some cases of malignant melanoma, it is well known that other cases are still difficult to treat. The research group clarified a new mechanism of melanoma development mediated by GREB1 Is4 and demonstrated that it represents a potential new target for new melanoma therapy

Cancer cells are characterized by their repeated uncontrolled proliferation, and chemotherapy has traditionally been used to suppress cell proliferation by inhibiting the nucleic acids synthesis. In this study, the research group demonstrated that GREB1 Is4 stimulates the synthesis of its nucleic acid and melanomagenesis, promoting the proliferation of cancer cells.

Furthermore, the results of this study are of great social significance because GREB1 Is4 has been shown to be a therapeutic target in malignant melanoma, and antisense oligonucleic acids against GREB1 are expected to become new therapeutic agents in the future.

Special Notes

This research finding was published in Oncogene on 1 September, 2023.

Title:GREB1 isoform 4 is specifically transcribed by MITF and required for melanoma proliferation

Authors:Koei Shinzawa*, Shinji Matsumoto, Ryota Sada, Akikazu Harada, Kaori Saitoh, Keiko Kato, Satsuki Ikeda, Akiyoshi Hirayama, Kazunori Yokoi, Atsushi Tanemura, Keisuke Nimura, Masahito Ikawa, and Tomoyoshi Soga, Akira Kikuchi*(*corresponding authors)

This research was supported by Grants-in-Aid for Scientific Research (S, C) and the AMED-Project for Promotion of Cancer Research and Therapeutic Evolution and was conducted in collaboration with Departments of Genome Biology and Dermatology at Graduate School of Medicine at Osaka University, Research Institute for Microbial Diseases at Osaka University, and Institute for Advanced Biosciences at Keio University.

Research Achievements

・Using mouse model and human clinical samples of malignant melanoma, the research group comprehensively demonstrated that induction of GREB1 Is4 expression by the MITF transcription factor is important for the development and prognosis of malignant melanoma.

・The research group identified CAD, the rate-limiting enzyme for pyrimidine synthesis, as a binding protein for GREB1 Is4, and demonstrated that GREB1 Is4 is essential for pyrimidine synthesis in malignant melanoma by biochemical and metabolomic analyses.

・This study showed that antisense oligonucleic acid against GREB1 Is4 represents a new therapeutic target in malignant melanoma.

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