The invasion of human cells by the new coronavirus is a fundamental step in the body’s infection process.
A group of researchers from the State University of Campinas (Unicamp) and the University of São Paulo (USP) described how a human protein interacts with a viral protein, demonstrating one of the mechanisms used by the virus that causes Covid-19 to recruit cells and replicate.
The findings of the study, which was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), were published in the journal Frontiers in Cellular and Infection Microbiology.
In tests performed in vitro, in a laboratory environment, the researchers managed to inhibit the interaction between the molecules using a drug and, with that, they reduced the viral replication between 15% and 20%. With the result, the group hopes to contribute to the development of therapies against disease.
“The human protein known as PCNA [sigla para Proliferating Cell Nuclear Antigen] interacts with the M protein [matriz] of SARS-CoV-2, one of the molecules that make up the membrane of the virus and give it its shape. The discovery itself shows one of the ways in which the pathogen [agente causador de doença] manipulates the cell’s function in order to follow its life cycle”, explains Fernando Moreira Simabuco, a professor at Unicamp’s Faculty of Applied Sciences (FCA), in Limeira, who coordinated the study.
In the laboratory, the group used different techniques to show how the presence of the virus M protein in the body causes PCNA, a protein involved in DNA repair, to migrate from the cell nucleus – where it is normally found – to the cytoplasm, region where the organelles, responsible for important cellular functions, are located.
According to the researchers, this migration demonstrates that the viral and human proteins are interacting with each other, which is in line with the results seen by other methodologies.
Another way to verify the phenomenon was using a compound that inhibits the migration of proteins from the nucleus to the cytoplasm. Both in cells treated with a specific compound for PCNA and with another one that inhibits the migration of different proteins, including PCNA, the coronavirus had a replication between 15% and 20% less when compared to those that were in cells without any treatment.
“If we were thinking about a therapy, maybe this reduction wouldn’t be significant. However, the main objective was to demonstrate this interaction and that it can be a target for future treatments”, says Simabuco.
In collaboration with researchers from the Department of Pathology, Faculty of Medicine, USP, samples of lung tissue obtained during autopsies of patients who lost their lives due to the disease were also analyzed.
An increase in the expression of both the PCNA protein and gammaH2AX, a protein considered a DNA damage marker, was observed, which reinforces the results. “This data may indicate another consequence of the coronavirus infection”, says Simabuco.
The work has as its first author Érika Pereira Zambalde, a postdoctoral fellow at FCA-Unicamp under the supervision of Simabuco.
New way
The M protein is anchored, along with the E and S proteins, in the membrane that surrounds the entire SARS-CoV-2, and is the most abundant of the four main structural proteins of the virus, which take its name because they shape the microorganism. Therefore, it has been seen as a potential target for drugs and vaccines.
In turn, the spike protein S is the best known because of its role in binding to the human receptor, which has made it the target of the main current vaccines.
The human protein PCNA, in turn, is extensively studied in the context of cancer, the subject of a project conducted by Simabuco at FCA-Unicamp. In virus infection, however, very little is known about the role of this human protein.
The new article paves the way for further studies on this interaction between the coronavirus and the molecule, facilitating the development of treatments. A next step would be the validation of the findings in animal models, which is not yet predicted to happen, according to experts.
Part of the experiments was carried out at the Laboratory for the Study of Emerging Viruses (LEVE), coordinated by José Luiz Proença Módena at the Institute of Biology (IB) at Unicamp, with the support of FAPESP.
The study also had the collaboration of research groups coordinated by Armando Morais Ventura, professor at the Institute of Biomedical Sciences (ICB) at USP, and Henrique Marques-Souza, professor at IB-Unicamp.