Photo by Thomas Semkow
Preclinical research indicates that a member of the Mediator protein complex plays a key role in hematopoiesis.
Investigators found that MED12 was required for the survival of hematopoietic stem and progenitor cells (HSPCs).
The team said this finding, along with the fact that MED12 mutations have been linked to leukemia and solid tumor malignancies, suggests that targeting MED12 hyperactivity might be a useful strategy for treating cancers.
“Because MED12 appears to be so essential to hematopoiesis, our study points to it as a possible target for future anticancer therapies for both chronic and acute forms of leukemia,” said Iannis Aifantis, PhD, of NYU Langone Medical Center in New York.
“Our study also suggests that MED12 hyperactivation or loss of control is a possible explanation for what factors may trigger these cancers and other solid tumors.”
Dr Aifantis and his colleagues described their study in Cell Stem Cell.
The investigators first analyzed the effects of MED12 deletion in mice. Mice bred to lack MED12 died within 2 weeks of birth and showed evidence of aberrant hematopoiesis—namely, a “severe reduction of bone marrow and thymus cellularity.”
Adult mice that were engineered to lose expression of MED12 after the injection of an activating molecule experienced a “rapid” reduction in bone marrow cellularity, as well as reductions in spleen and thymus size. These mice also had low white blood cell and platelet counts and died within 3 weeks of MED12 deletion.
Subsequent analyses of the animals’ bone marrow showed that estimates of HSPCs in each mouse fell from nearly 150,000 to 15,000 within 4 days of injection. Within 10 days, there were no HSPCs left.
Deleting MED12 was also lethal for human HSPCs. Colonies of CD34+ cells dropped from an average of 25 per plate to 5 per plate within 10 days of MED12 deletion.
On the other hand, MED12 did not affect the survival of other cell types. For example, MED12 deletion did not impact mouse embryonic fibroblasts, embryonic stem cells, or hair follicle stem cells.
In addition, deleting members of the Mediator kinase module besides MED12—MED13, CDK8, or CYCLIN C—did not have a significant effect on HSPCs and did not kill mice. The investigators said this provides further evidence that MED12—by loss of its function alone—is essential for hematopoiesis.
The team found that MED12 deletion destabilizes P300 binding at lineage-specific enhancers, which results in H3K27Ac depletion, enhancer de-activation, and the consequent loss of hematopoietic stem cell gene expression signatures.
As a next step, the investigators plan to screen blood samples from cancer patients for signs of MED12 mutations and uncontrolled HSPC development.
The team also hopes to determine the biological mechanisms involved in MED12 hyperactivation and identify drug molecules that could block MED12 hyperactivity and serve as potential MED12 inhibitors.
