National Health Research Institutes

NHRI researchers find MAP4K3 as a key to COVID-19 infection

August 11, 2022

Scientists with Taiwan’s National Health Research Institutes (NHRI) have discovered MAP4K3 as a key to COVID-19 pathogenesis.

Over the past two and a half years, SARS-CoV-2 infection (also known as COVID-19) has spread around the world, infecting more than 560 million people and killing millions.

The major entry receptor of SARS-CoV-2 on epithelial cells is angiotensin-converting enzyme 2 (ACE2). SARS-CoV-2 infection of airway epithelium is quite efficient; however, why ACE2 levels are generally low in airway epithelial cells of healthy individuals had puzzled scientists. After two years of diligent research, distinguished investigator Dr. Tse-Hua Tan and assistant investigator Dr. Huai-Chia Chuang, both with NHRI’s Immunology Research Center, recently discovered that a key kinase, MAP4K3 (also named GLK), controls SARS-CoV-2 infection. For this study, Dr. Tan and Dr. Chuang collaborated with Dr. Yen-Hung Chow, an investigator with the National Institute of Infectious Disease and Vaccinology at NHRI, on the live SARS-CoV-2 infection mouse model. They demonstrated that GLK-stabilized ACE2 proteins and GLK-induced ACE2-containing exosomes are important pathogenic factors for COVID-19. Their work was published in July in EMBO Molecular Medicine.

In the summer of 2020, Dr. Tan’s research team analyzed single-cell RNA sequencing (scRNA-seq) data from COVID-19 patients and surprisingly found that induction of GLK levels in epithelial cells is correlated with COVID-19 severity and with cellular vesicle pathways. To understand the role of GLK overexpression in epithelial cells of COVID-19 patients, the research team performed mass spectrometry-based analysis and biochemical experiments. The researchers found that the spike protein of SARS-CoV-2 induces GLK mRNA levels in the infected epithelial cells. GLK phosphorylates and stabilizes ACE2 by blocking UBR4-mediated proteasomal degradation of ACE2. This is the first report that reveals the novel phosphorylation residues, ubiquitination residues, kinase, and E3 ubiquitin ligase of the ACE2 protein. In addition, GLK overexpression in epithelial cells induces release of the ACE2-containing exosomes, resulting in increased ACE2 proteins and enhanced SARS-CoV-2 infection of otherwise less susceptible cells. The GLK-phosphorylated ACE2 and ACE2-containing exosomes are also detectable in the sera of COVID-19 patients. This mechanism provides an explanation for why ACE2 levels are very low in airway epithelial cells of normal individuals, whereas SARS-CoV-2 infection of airway epithelium is quite efficient.

Using adoptive transfer of ACE2-containing exosomes into recipient mice, SARS-CoV-2 pseudovirus (only containing spike protein)-infected humanized ACE2 knockin mice, and live SARS-CoV-2-infected humanized ACE2 transgenic mice, the research team demonstrated the pathogenic function of GLK overexpression in COVID-19. Remarkably, treatment of the GLK inhibitor verteporfin attenuates ACE2 protein levels and ACE2-containing exosomes, leading to inhibition of SARS-CoV-2 pseudovirus infection in mice. The data suggest that verteporfin could be repositioned to attenuate SARS-CoV-2 infection.

Notably, GLK levels are induced by the spike protein, which is the main content of COVID-19 vaccine. In addition, GLK overexpression in immune cells contributes to inflammatory responses; thus, the adverse effects of COVID-19 vaccine may also be induced by the spike protein-stimulated GLK in immune cells (such as macrophages or T cells).