Dying Cells Can Protect Their Stem Cells From Destruction

Summary: Cells dying because of chemotherapy and radiation can send a warning to closeby stem cells. The chemical signals lets both the tumour forming and tissue repair cells to escape the similar fate. And this explains why several cancers come back after responding to the treatments, and could lead to more effective and new cancer drugs that might block such signals that stop the cells from moving into the programmed death of the cells.

Yalan Xing, the lead author and postdoctoral in the UW department of Biochemistry said that “the findings of a study may explain why many types of cancers come back after responding to their treatment in the beginning, and could also lead to more effective and new cancer drugs.

Most tissues in human beings harbor adult stem cells. Such cells revive endlessly, and also generate daughter cells that can develop into a wide array of cell types. This in turn makes it possible for the bodies to grow and to restore aging or damaged cells. However, many different types of cancers harbor similar cells known as, “cancer stem cells”, or “tumour initiating cells”.

In addition to this, both types of cells share one more property- they can often survive chemotherapy and radiation. In the case of stem cells, this specific ability lets our bodies recover from such treatments. However, in the second case of tumour initiating cells, these treatments make it possible to resist them and return.

Hannele Ruohola Baker and Yalan Xing, associate director, professor of biochemistry at UW institute tried to figure out how such cells survive exposure to what should be fatal doses of chemotherapy and radiation. They looked at the natural weeding of the unwanted cells known as apoptosis, and also noticed the adult cells in the fruit fly.

Apoptosis is also called programmed cell death. It is a systematic clean-up procedure that our bodies follow, in order to ward off cells that are aged, damaged, or no longer required. In the case of chemotherapy and radiation exposure, damage to the DNA of cells from such treatments brings about apoptosis and death of the cells.

The researchers also show in their study that after exposure to such treatments, dying daughter cells also release a protein known as, Pvf1. This is similar to human protein known as, angipoietin which binds to all receptors on closeby mother stem cells known as, Tie receptors. This in turn causes the stem cells to generate a small piece of RNA, known as micro Bantam that crushes the production of a key protein known as, Hid, required to trigger apoptosis.

The aftermath is that, although the stem cells may have suffered DNA damage, but they are prevented from any sort of self-destruction.

Xing also said that ” indispensably, the children tell the mother to protect herself”.

Since they are safeguarded from instantly destroying themselves, so the stem cells stay alive until it is time for them to revive tissue. The researchers also propose that as these cells get ready to regenerate, they trigger a battery of mechanisms that revive damaged DNA. The dying daughter cells totally block apoptosis, thereby enabling their mother cells to stay alive until they have chance of recovering from the treatment.

Hannele Ruohola Baker also said that by protecting the mother cells, the dying daughter cells safeguard the only cell type that can revive the adult stem cell.

There are similar proteins and genes in human cancers that re playing the same role of safeguarding the tumour initiating cells from damage. As a result, these cells stay alive and the cancer returns. So by blocking all Tie receptors, it may be possible to totally block the securing signal from the daughter cells, and hence let the programmed death of the cell to move in the mother stem cells, and thereby prevent cancer.