Nuclear DLC1 exerts oncogenic function through association with FOXK1 for cooperative activation of MMP9 expression in melanoma

Xintao Yang,May Pui Lai Cheung,Martin Cheung,Irene Oi-Lin Ng,Rakesh Sharma,Feng Hu,Xin-Yuan Guan,Yufei Jiao,Shan Yu,Kelvin K W Wong,Hong Lok Lung,Xuelai Liu,Leo Tsz On Lee,Jessica Aijia Liu

doi:10.1038/s41388-020-1274-8

Abstract

A Rho GTPase-activating protein (RhoGAP), deleted in liver cancer 1 (DLC1), is known to function as a tumor suppressor in various cancer types; however, whether DLC1 is a tumor-suppressor gene or an oncogene in melanoma remains to be clarified. Here we revealed that high DLC1 expression was detected in most of the melanoma tissues where it was localized in both the nuclei and the cytoplasm. Functional studies unveiled that DLC1 was both required and sufficient for melanoma growth and metastasis. These tumorigenic events were mediated by nuclear-localized DLC1 in a RhoGAP-independent manner. Mechanistically, mass spectrometry analysis identified a DLC1-associated protein, FOXK1 transcription factor, which mediated oncogenic events in melanoma by translocating and retaining DLC1 into the nucleus. RNA-sequencing profiling studies further revealed MMP9 as a direct target of FOXK1 through DLC1-regulated promoter occupancy for cooperative activation of MMP9 expression to promote melanoma invasion and metastasis. Concerted action of DLC1–FOXK1 in MMP9 gene regulation was further supported by their highly correlated expression in melanoma patients’ samples and cell lines. Together, our results not only unravel a mechanism by which nuclear DLC1 functions as an oncogene in melanoma but also suggest an unexpected role of RhoGAP protein in transcriptional regulation.

Highlights

Supplementary information The online version of this article contains supplementary material, which is available to authorized users.Melanoma is considered the most aggressive form of skin cancer, accounting for over 80% of skin cancer deaths in the United States [1]
Consistent with its tumor-suppressor function, deep (6.9%) and shallow (61.5%) deletion of the deleted in liver cancer 1 (DLC1) gene were more frequently detected in human hepatocellular carcinoma than that of melanoma that correlated with lower DLC1 mRNA expression levels among liver tumor samples (Fig. 1a, b) [26]
matrix metalloproteinase 9 (MMP9) remained low in DLC1 KD cells overexpressing both DLC1 and truncated versions of Forkhead Box K1 (FOXK1), which exhibited a lack of interaction with DLC1 (Figs. 3e and 5h and Supplementary Fig. 7k)

Summary

Introduction

The high mortality rate among melanoma patients is directly related to the metastatic properties of the tumor. Over 50% of melanoma patients harbor the BRAF. Department of Pathology, The Second Affiliated Hospital of Harbin Medical University, Harbin, China. Centre of Reproduction, Development and Aging, Faculty of Health Sciences, University of Macau, Taipa, Macau, China mutation, which leads to constitutive activation of the oncogenic signaling pathways together with dysregulated expression of cancer driver genes, resulting in the neoplastic transformation of embryonic neural crest (NC)-derived melanocytes located in the basal layer of the skin epidermis into metastatic melanomas [2, 3]. Despite improved overall survival of patients with metastatic melanoma treated with an inhibitor to target BRAF mutation, cancer can rapidly acquire resistance to the treatment that limits its long-term efficacy [4]. There is an urgent need to identify new factors in governing melanoma colonization as alternative therapeutic targets

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Conclusion