Understanding how cells die is critical for developing new treatments for a wide range of disorders, whether the goal is to kill cancer cells or maintain healthy cells alive in the face of other ailments like major infections or strokes.
Two new research from Washington University School of Medicine in St. Louis has discovered a previously unknown cell death process known as lysoptosis and show how it could lead to new cervical cancer treatments.
Both research were published in the Nature journal Communications Biology on Jan. 12 and looked at data from roundworms, mice, and human cells. A protein called SERPINB3 is found in the blood of people with cervical cancer and other tumor types.
When the gene that makes SERPINB3 is missing in cervical cancer cells, the tumor cells die more easily when subjected to radiation exposure, according to recent research. Similarly, C. elegans, microscopic roundworms that lack the corresponding gene, perish more quickly when exposed to challenges in their habitats.
“It’s been known for a long time that high levels of this protein in the blood are a marker of cervical cancer and other squamous cell cancers the higher the protein levels in the blood, the worse the prognosis,” said Stephanie Markovina, MD, Ph.D., assistant professor of radiation oncology.
“We wondered if this protein may be doing something to protect cancer. We thought it was possible that the gene was protecting the cancer cells from stress in the same way the equivalent roundworm gene was protecting C. elegans from stress.”
Markovina collaborated with Gary Silverman, MD, Ph.D., the Harriet B. Spoehrer Professor and head of the Department of Pediatrics; and Cliff J. Luke, Ph.D., associate professor of pediatrics, who had been studying this pathway in C. elegans and mice.
It’s been known for a long time that high levels of this protein in the blood are a marker of cervical cancer and other squamous cell cancers the higher the protein levels in the blood, the worse the prognosis. We wondered if this protein may be doing something to protect cancer. We thought it was possible that the gene was protecting the cancer cells from stress in the same way the equivalent roundworm gene was protecting C. elegans from stress.
Stephanie Markovina
“One day I noticed that the worms that had the equivalent gene knocked out were all dying,” Luke said. “I realized that instead of putting the roundworms in the normal saline or saltwater that we used, I accidentally put them in regular water. The normal roundworms were totally fine, but the worms lacking the worm-equivalent of the human SERPINB3 gene all died. The plain water was a source of stress, and we determined that they lacked the gene that protects them from stress-induced cell death. We then wondered if this cell death was conserved in mammals. Similar to C. elegans, we showed that intestinal mouse epithelial cells were more sensitive to stress when missing the mouse equivalent of human SERPINB3.”
The researchers discovered that this mechanism of cell death is activated in a specific compartment of the cell known as the lysosome, a key waste-management center responsible for recycling or disposing of cellular waste in roundworms, mice, and cervical cancer.
Serpin genes, which defend against cell death triggered by the lysosome (lysoptosis) and the cell death pathway itself, were discovered to be conserved throughout species, from roundworms to humans.
“There are many different cell death pathways, and understanding the specific routes involved in each individual pathway is vital for the treatment of disease,” said Silverman, also a professor of cell biology and physiology, and of genetics, and executive director of the Children’s Discovery Institute at Washington University School of Medicine and St. Louis Children’s Hospital.
The lysosome houses some of the body’s most potent enzymes. If lysosomes leaked just a little, they may cause irreversible damage to the cell. As a result, most researchers rejected their significance in cell death because the consequences would be disastrous. It was expected that cells would have several defenses in place to prevent this from happening.
“Our work shows that this is not the case,” he said. “Lysosomes leak a bit all the time, and proteins like SERPINB3 are there to neutralize these enzymes if they get out of the lysosome. When SERPINB3 levels are low or absent, or if the stress is strong enough to cause a big lysosomal leak, the cells die quickly, ravaged by the lysosomal enzymes. The cells appear to explode and spew their contents out into the extracellular space, where it triggers an intense inflammatory response. So, lysoptosis signifies an active, stand-alone cell death process that dramatically destroys the cell. This process is very different from apoptosis, in which the cell quietly implodes and the cell debris is cleaned by neighboring cells.”
Markovina employed the gene editing technology CRISPR to remove the SERPINB3 gene from cervical cancer cells in order to examine its consequences. When cervical cancer cells were put into mice without this protective gene, the researchers discovered that they were more sensitive to the stress of chemotherapy and radiation.
The researchers are looking for medications that shut down the SERPINB3 gene in cervical cancer cells, allowing chemotherapy and radiation to kill them more quickly.
“As soon as we have a candidate drug, we hope to get it into clinical trials as soon as possible,” said Markovina, who treats patients with gynecological cancers at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine.
Luke also mentioned that in some cases, such as viral or bacterial infections, a particular medication that avoids this type of cell death can be useful.
“We’re also screening drugs for potential therapies that would enhance the cell protection that this gene confers,” Luke said. “For example, premature infants have a high risk of developing a devastating inflammatory disease called necrotizing enterocolitis, in which the cells of the interior lining of the gut die off. In this case, we would be interested in finding ways to dial up the expression of SERPINB3 to protect against cell death in the gut.”
Added Silverman, “Evidence suggests that lysoptosis is how cells die after massive injury, such as from heart attacks or strokes, or in highly inflammatory conditions like inflammatory bowel disease or necrotizing enterocolitis.”
“In some instances, we would want to manipulate lysoptosis to help kill tumor cells, and in others, we would want to block it when it is inappropriately triggered. We are hopeful this new knowledge can lead to novel therapies for diseases in which this type of cell death plays a key role.”
