Disabling One Protein May Provide A Cure to The Common Cold

Over hundreds of years, advancements in technology and methodology have allowed scientists to cure tetanus, rabies, yellow fever, smallpox, and countless other diseases damaging to humans. Yet to this day, scientists have consistently failed in their efforts to find a cure for the most common infection worldwide: the cold. Ever since the 1950s, the cure for the cold was an assiduous challenge. Vaccines fail to provide immunity due to the wide range of virus strains with different genetic makeup and receptors that cause the cold. To make matters worse, these viruses are highly mutation prone and develop drug resistance quickly. A subgroup of cold-causing viruses are rhinoviruses, which account for three-fourths of cold infections. Rhinoviruses are part of the genus Enterovirus, which causes a wide range of diseases such as polio, acute flaccid myelitis, encephalitis (inflammation of the brain), and myocarditis (inflammation of the heart). Scientists uncovering a cure for all enterovirus-causing diseases (which meant immunity to several hundred different viruses) seemed like an unachievable task. However, a few scientists at Stanford University believe they have found a way to cure the cold, polio, myelitis, and perhaps all diseases caused by enteroviruses.

What research was conducted at Stanford and what were the results?

Jean Carette, Ph.D., associate professor of microbiology and immunology at Stanford, and his team published “Enterovirus pathogenesis requires the host methyltransferase SETD3” in the journal Nature Microbiology on September 16, 2019. Their research showed that disabling one gene prevented the replication of multiple enteroviruses in human and mice cells. Jean Carette’s team first began their investigation by culturing 20,000 human cells. The cells were randomly edited by CRISPR/CAS9 to have one gene silenced or rendered dysfunctional in order to figure out which proteins were important in enterovirus fecundity. Each cell was injected with RV-C15, a rhinovirus known to exacerbate asthma in children, and EV-C68, an enterovirus implicated as a factor behind myelitis. Both RV-C15 and EV-C68 are enteroviruses, but they are taxonomically and genetically different and require different proteins to replicate. Yet one type of cell survived both viruses—cells without the SETD3 gene. The gene coded for an enzyme was called SET domain containing 3, or SETD3 which Carette notes “was clearly essential to viral success, but not much was known about it.”

The team then engineered and grew human cells without the SETD3-producing gene and tried to infect them with multiple enteroviruses, such as EV-D68 (known to cause the cold), poliovirus, three different types of rhinovirus, and two varieties of coxsackievirus, which can cause myocarditis. None of the viruses were able to replicate inside these cells, leaving the cells healthy and able to fend off the virus. The researchers observed a 1,000-fold reduction in a viral replication inside human cells lacking SETD3. “The virus gets in, but it can’t start making photocopies of itself,” Carette says. “It requires this SETD3 as an essential part of this photocopier.” When the SETD3- producing capability was restored, the viruses proved capable of pillaging the cells.

What are the limitations presented by the mechanism found in the research? What must be done before a cure is implemented?

After using human cells, Carette’s team conducted a study with genetically modified mice without the SETD3 gene. Working with newborn mice, Carette’s team injected two deadly types of enteroviruses (that cause paralysis and brain inflammation) into the mice’s brain. All the mice without SETD3 were immune, displaying none of the symptoms caused by the viruses. “To our great surprise, if you make mice that lack this SETD3 enzyme, they’re viable and apparently healthy,” Carette says.

There was one flaw in the mice without SETD3 that the normal mice did not have: the modified mice had more difficulty giving birth. Biologist Or Gozani of Stanford, a co-senior author of the new study, and his colleagues found that during a process called methylation, the SETD3 protein modifies actin, a protein important in muscle contraction. “It seems actin methylation is important for smooth muscle contraction during childbirth,” Carette says. Since the SETD3-producing gene is highly important to cellular function, Carette’s team noted the risk of conducting a human trial with the removal of the SETD3 gene. Further research revealed a newfound discovery that eliminated replication without, in fact, removing the gene. The replication of enteroviruses and SETD3 were connected via another protein: the viral protein 2A.

In Carette’s research paper, he notes that “SETD3 specifically interacts with the viral 2A protease of multiple enteroviral species. 2A mutants that retain protease activity (the breakdown of proteins) but are unable to interact with SETD3 are severely compromised in RNA replication.” Without the interaction of the SETD3 protein and the viral protein 2A, the virus’ genome is compromised which blocks the viruses’ pathway of replicating. This meant that in order to completely stop viral replication, scientists must find a way to stop the interaction of the two proteins. “This gives us hope that we can develop a drug with broad antiviral activity against not only the common cold but maybe all enteroviruses, without even disturbing SETD3’s regular function in our cells,” Carette explains.

Antiviral medication and medicine traditionally were based upon a virus’s genetic makeup. However, recent strides in medical science shifted from an approach of focusing on only the virus to the second part of the equation: the host cell. A cold virus can itself mutate, but the binding site on human cells for a certain strain is always the same. “Drug resistance can be a problem for these viruses that rapidly mutate,” Carette explains. “This is especially seen in traditional antiviral therapy, where the drug directly targets a viral protein because the virus can mutate in a way that it loses interaction with the drug. Our approach is different because we target a human protein that the virus depends on, therefore [creating] a higher barrier to drug resistance.”

Researchers think their best bet is to search for a drug that blocks the human protein and its viral counterparts from interacting or one that destroys the human protein only when it is interacting with viral ones. But those types of drugs are still a long way off. “The question is always ‘When can I buy it over the counter?’” Carette says. “Drug development takes time.” If scientists can discover a way to interrupt the interaction of the viral 2A protein and SETD3, the medical industry may have access to a viable cure for asthma, encephalitis, myocarditis, polio, and the common cold. Until then, sore throats and runny noses will remain the norm.