A contagious tumor

Cancer cells can infect healthy ones

Kirill Stasevich, "Science and Life"

Cancer is not considered a contagious disease. Although some of its varieties can be caused by viruses, even in this case it will be quite difficult to get a full–fledged disease after infection - the vital activity of the oncovirus does not always lead to the development of a malignant tumor. Two exceptions, when the tumor is easily transmitted and at the same time is highly aggressive, are dangerous only for dogs (transmissible venereal sarcoma of the dog) and the Tasmanian devil marsupial (the so-called Tasmanian devil facial tumor).

However, if cancer is almost not transmitted from person to person, then it can pass from cell to cell very easily. This conclusion was reached by researchers from the M. D. Anderson Cancer Center at the University of Texas, who discovered how malignant cells spread the disease to healthy neighbors using RNA molecules. Many cells, including cancer cells, throw out into the intercellular space small membrane vesicles-exosomes containing proteins, DNA and RNA. In some cases, it's just molecular garbage, but it happens that exosomes contain signaling molecules with which one cell sends a message to another.

It has previously been shown that malignant cells create more exosomes than normal cells. Raghu Kalluri and his collaborators found that the membrane vesicles secreted by cultured cancer cells differ markedly in content: in fact, they are small factories producing microregulatory RNAs. As you know, such RNAs do not carry any information about proteins, but they can influence the activity of other genes.

When exosomes taken from human breast cancer cells were injected into healthy mice, the animals began to develop a tumor. If the mice were injected with exosomes of normal cells, then no tumor was obtained. Similarly, mice remained healthy if the mechanism of synthesis of microregulatory RNAs was turned off in the cancer exosomes that they were injected with. The experiment was repeated with samples taken not from the culture of malignant cells, but from sick people. The effect was the same: 8 out of 11 samples provoked cancer degeneration in cell culture and tumor development when administered to mice. Exosomes isolated from the blood of healthy people were harmless in this sense.

That is, the membrane vesicles acted as intercellular infectious agents, they carried molecular instructions (in the form of microRNAs) for reprogramming a healthy cell into a malignant one. In other words, cancer can spread through the body not only with the help of wandering metastatic cells, but also simply turning normal cells into sick ones. The results of the experiments were published by the authors in Cancer Cell (Melo et al., Cancer Exosomes Perform Cell-Independent microRNA Biogenesis and Promote Tumorigenesis).

It is not yet clear how far cancer exosomes can travel through the body, but judging by the fact that they were isolated from the blood, they have no problems with transportation. Although even if the "contagious effect" takes place at a short distance from the tumor, the problem does not disappear anywhere – something still needs to be done with malignant infection. And to understand exactly what can be done here, you need to find out exactly how a bad membrane bubble contacts a normal cell, why a normal cell takes a dangerous load, and how regulatory molecules from the tumor act in it. In the meantime, researchers will find out all this, exosomes can be used in diagnostic tests to monitor the dynamics of the disease.

In addition to the miRNAs described here, "contagious" cancer exosomes contain many other biomolecules.
Diagram from the article "The genomic and proteomic content of cancer cell-derived exosomes"
(Meredith C. Henderson and David O. Azorsa, Front. Oncol., 2012) – VM.
 

Portal "Eternal youth" http://vechnayamolodost.ru 27.10.2014