Unraveling the pro-metastatic activity of Nm23-H1

Abstract

Human nucleoside diphosphate kinase 1 (also known as NDPKA or Nm23-H1) was identified and studied as a metastasis suppressor over the past decades. It has received much attention for its ability to suppress metastasis in several human cancers including breast cancer and melanoma. Therapeutic strategies that aim to upregulate Nm23-H1 expression have also been explored in cancer treatment to suppress metastasis. However, there is evidence to suggest that Nm23-H1 can promote the migration of human neuroblastoma NB69 cells in vivo. Clinical studies have likewise hinted at a positive correlation between Nm23-H1 expression and poor diagnosis in several cancer types including brain cancer, leukemia and neuroblastoma, which is surprisingly opposite to its role as a metastasis suppressor. In this study, it was demonstrated that Nm23-H1 and another isoform of the Nm23 family, Nm23-H2, can promote the migration of T98G glioblastoma, 1321N1 astrocytoma, and SH-SY-5Y neuroblastoma cells. Cell invasion of 1321N1 cells was also increased upon expression of Nm23-H1. However, neither shRNA nor siRNA knockdown of Nm23-H1 alone was sufficient to reverse the pro-metastatic phenotype. Nm23-H1 expression induced ERK phosphorylation in 1321N1 cells, potentially contributing to an aggressive phenotype unlike other cancers where ERK signaling is downregulated by Nm23-H1.

Interestingly, emerging evidence also suggest that Nm23-H1 exhibits transcription factor activity in addition to its enzymatic activities. Based on these findings, it is hypothesized that Nm23-H1 may act as a transcription factor to regulate genes that drive a pro-metastatic function. The pro-migratory function of Nm23-H1 was significantly diminished in several Nm23-H1 mutants that are devoid of DNA binding activity, indicating that transcriptional pathways are indeed involved in cell migration. The binding between Nm23-H1 and promoter regions of c-MYC, ALDOC, and TP53, was confirmed by ChIP and EMSA. RNA-sequencing revealed that several metastasis-promoting genes including IL6, IL26, FGG and FGF19 were upregulated by Nm23-H1, whereas metastasis-inhibiting genes such as RANBP3L, KLF17, THRSP and PRELP were downregulated. Interestingly, many of these genes were regulated oppositely in MDA-MB-231 cells in which Nm23-H1 acts as a metastasis suppressor. RANBP3L, a target gene with tumor suppressor activity, was downregulated with the highest fold change. Protein expression of RANBP3L was also downregulated in 1321N1 cells and may contribute to the pro-metastatic activity of Nm23-H1. In addition, Nm23-H1 increased the levels of multiple secreted proteins that participate in cancer signaling pathways, including GDF15, IL6, and FGF19. These secreted proteins activated STAT3 phosphorylation, which is a contributor of metastasis promotion. Collectively, these findings indicate that Nm23-H1 acts a transcription factor to regulate cancer-related genes that drive a pro-metastatic function in astrocytoma and potentially other cancer cell types.

Date of Award	2023
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Yung Hou WONG (Supervisor)