Repair proteins protect cancer cells from T cell attack
Cancer cells have some clever strategies at the ready to protect themselves from attacks by the immune system. One of them: repair proteins that plug small holes in the cell wall.
Cancer cells are extremely adept at withstanding the body's own defenses. One reason for this is that they can repair themselves very quickly during an immune cell attack with the help of special proteins. The team led by Alex Ritter of the U.S. biotechnology company Genentech has now presented the protective measures of the cancer cells in the scientific journal "Science".
Certain immune cells, the cytotoxic T lymphocytes, are specialized in destroying infected cells as well as tumor cells. Once they have identified their target, they secrete various cytotoxins: The protein perforin forms pores in the cell membrane through which the enzyme granzyme enters the cell. There it initiates programmed cell death, apoptosis. However, cancer cells have found an effective way to protect themselves from the T-cell attack, as Ritter's team has discovered: they form protein complexes called Endosomal Sorting Complexes Required for Transport (ESCRT), which close the small pores. This makes it harder or impossible for granzymes to enter the tumor cell and knock it out.
First, the researchers observed the ESCRT proteins inside cancer cells in real time and with the help of a special laser microscope. They found that the ESCRT proteins migrated to the damaged cell membrane immediately after a T-cell attack. In another experiment, the researchers blocked the protein complexes in their function. As a result, the defense cells were able to kill more tumor cells than before.
Cancer cells have developed a number of additional strategies that help them evade the immune system: The malignant cells can make themselves "invisible" to the immune system by hiding surface molecules that are typical for them. Some cancer cells are also able to bind to T cells and block them out. With the help of immunotherapies, doctors hope to circumvent these mechanisms so that the cancer cells can no longer escape the body's own defenses.
Spectrum of Science
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Originalartikel auf Spektrum.deTitelbild: © Meletios Verras / Getty Images / iStock (Ausschnitt)
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