The Sept4 Gene Prevents Stem Cells From Turning Cancerous

Stem cells, those prodigious precursors of all the tissues in our body, can make almost anything, given the right circumstances, but unfortunately that can also cause cancer sometimes. However research from Rockefeller University has shown that having too many stem cells, or stem cells that live too long, can increase the odds of developing cancer. By identifying a mechanism that regulates programmed cell death in precursor cells for blood, or the stem cells that make all blood-based cells (hematopoietic stem cells), these researchers have connected the death of such cells to a later susceptibility to develop tumors in mice. This work also provides evidence of the potentially carcinogenic downside to stem cell treatments, and suggests that there is a balance between stem cells’ regenerative power and their potentially lethality.
Research associate Maria Garcia-Fernandez and head of the Strang Laboratory of Apoptosis and Cancer Biology, Hermann Steller, and colleagues explored the activity of a gene called Sept4. Sept4 encodes a protein called ARTS that increases programmed cell death, or apoptosis, by antagonizing other proteins that prevent cell death. ARTS was originally discovered by Sarit Larisch while visiting Rockefeller, and is lacking in human leukemia and other cancers, which suggests that it suppresses tumors. To study the role of ARTS, the experimenters bred a line of mice genetically engineered to lack the Sept4 gene.
For several years, Garcia-Fernandez studied cells that lacked ARTS. He goal was to look for signs of trouble relating to cell death. However, in mature B and T cells, she could not find any. Then when she examined these cells at earlier and earlier times in their development she found crucial differences between the stem cells that gave birth to the progenitor cells that eventually became the mature B and T cells and the stem cells themselves. Newborn ARTS-deprived mice had about twice as many hematopoietic stem cells as their normal, ARTS-endowed peers. Furthermore, these stem cells were extraordinary in their ability to survive experimentally induced mutations. “The increase in the number of hematopoietic progenitor and stem cells in Sept4-deficient mice brings with it the possibility of accelerating the accumulation of mutations in stem cells,” says Garcia-Fernandez. “They have more stem cells with enhanced resistance to apoptosis. In the end, that leads to more cells accumulating mutations that cannot be eliminated.”
In fact the ARTS-deprived mice developed spontaneous tumors at about twice the rate of their controls. Herman Steller said, “We make a connection between apoptosis, stem cells and cancer that has not been made in this way before: this pathway is critically important in stem cell death and in reducing tumor risk…. The work supports the idea that the stem cell is the seed of the tumor and that the transition from a normal stem cell to a cancer stem cell involves increased resistance to apoptosis.”
ARTS interferes with molecules called inhibitor of apoptosis proteins (IAPs), which prevent cells from undergoing programmed cell death. When cells accumulate too much damage to work properly, programmed cell death ensues, and the damaged cell is replaced by a new cell. Programmed cell death is also called “apoptosis.” By inhibiting these IAPs, under the right circumstances ARTS helps to take the brakes off the process of apoptosis that normally permits the cell to die on schedule. Pharmaceutical companies are working to develop small molecule IAP antagonists, but this research is the first to show that inactivating a natural IAP antagonist actually causes tumors to grow, according to Steller. It also suggests that premature silencing of the Sept4/ARTS pathway at the stem cell level may herald cancer to come.
“This work not only defines the role of the ARTS gene in the underlying mechanism of mammalian tumor cell resistance to programmed cell death, but also links this gene to another hallmark of cancer, stem and progenitor cell proliferation,” said Marion Zatz, who oversees cell death grants, including Steller’s, at the NIH’s National Institute of General Medical Sciences. “The identification of the ARTS gene and its role in cancer cell death provides a potential target for new therapeutic approaches.”

Japanese Scientists Convert Induced Pluripotent Stem Cells into Liver Cells

Research groups from Okayama University Graduate School of Medicine have made remarkable breakthroughs in liver transplantation. One team found that mouse induced pluripotent stem cells can form liver cells. The second group showed that transplantation of liver cells from another animal species could reverse the symptoms of liver failure in mice.

The first research team use mouse induced pluripotent stem cells (iPSCs) and subjected them to a protocol to convert them into liver cells. They cultured the iPSCs in free-floating cultures to form embryoid bodies. Embryoid bodies (EBs) are cell aggregates derived from embryonic stem cells when they are grown in non-attached, free floating cultures, like a hanging drop. EBs can also be induced by plating embryonic stem cells (ESCs) on non-tissue culture treated plates or by growing them in spinner flasks. Once the cells aggregate, they differentiate to a limited extent to roughly recapitulate embryonic development. EBs are composed of a large variety of differentiated cell types. However, EB differentiation is largely disorganized.

The EBs were then treated with a growth factor called “fibroblast growth factor” and activin for three days to induce the formation of endodermal tissues. On the eighth day of differentiation, they treated the cells with “hepatic growth factor” for eight days. After 16 days, they had functional liver cells, and this protocol seemed to work quite well.

A variety of genetic and metabolic tests showed that these cells were liver cells. They expressed liver-specific enzymes like urea cycle enzymes, the iron transport protein transferrin, asialoglycoprotein receptor (ASGR), and the all-important liver-specific protein, albumin. Metabolically, the iPSC-made liver cells also metabolized ammonium, which is a liver-specific activity.

A major limitation for cell-based therapies for the treatment of liver diseases is the shortage of livers for transplantation, and the risk of rejection by the immune system if the transplanted tissue is not well matched with that of the donor is also a stark problem. This technology, however, provides the means to make transplantable liver cells from someone else’s own somatic cells.

The lead author of this study, Masaya Iwamuro said, “The ability to make iPS cells from somatic cells has implications for overcoming both immunological rejection and ethical issues associated with embryonic stem cells… Our study will be an important step in generating hepatocytes from human iPS cells as a new source for liver-targeted cell therapies…In the future, studies will generate new therapies that include the transplantation of iPS cell-derived hepatocytes without immunological barrier, in vitro determination of toxicity, and the development of personalized health care by evaluating drugs for efficacy and toxicity on patient-specific hepatocytes,”

The second study used pig liver cells for mice with failed livers. Because of the lack of suitable livers for transplantation, Naoya Kobayashi argued that the greater supply of pig liver cells suggest that once technical issues are overcome, pig liver cells might be transplanted successfully into human livers. In their recent study, Kobayashi and colleagues successfully transplanted pig liver cells into mice with acute liver failure.  Their transplantations caused the mice with liver failure to survive and their symptoms subsided.

Kobayashi provided this statement: “Using xenogenic hepatocytes from animals such as pigs might be advantageous for treating acute liver failure in humans…. Hepatocytes are the main active cells in the liver. However, removal from the liver causes hepatocytes major stress and potential loss of function. We tested a scaffold to improve the success of hepatocyte xenotransplantation…. In this xenotransplantation model, we found that the SAPNF has an excellent ability to promote hepatocyte engraftment and maintains tremendous hepatocyte functions capable of rescuing mice from acute liver failure. Dr. Kobayashi collaborated with colleagues from the Baylor (Texas) University Institution for Immunology Research.