Mutations in key blood cell protein disrupt development, predispose to leukemia

A new study of a subset of human disease-associated protein mutants shifts this notion, and finds that some AML-associated GATA-2 variants retain and even have greater activity — but in a corrupted way.

The study, published earlier this month in the Proceedings of the National Academy of Sciences, finds that some GATA-2 mutations generate a form of GATA-2 that promotes myeloid cell development. This finding has implications for the development of AML, a blood cancer that affects people of all ages, and a better understanding of GATA-2 function in normal and leukemic cell regulation may lead to improved targeted therapies.

“The paradigm was, if you have GATA-2 mutations that cripple its function, then protein levels would be insufficient to carry out GATA-2’s mission to regulate blood cell development. That precarious state would create a predisposition to develop leukemia, and in certain circumstances, may cooperate with mutations in other genes to cause leukemia,” said the study’s senior author, Emery Bresnick, PhD, a professor of cell and regenerative biology at the University of Wisconsin School of Medicine and Public Health, director of the UW–Madison Blood Research Program and co-director of the Genetic and Epigenetic Mechanisms Program of the UW Carbone Cancer Center. “Unexpectedly, certain GATA-2 disease mutants retain the capacity to stimulate cells to differentiate, but only along the myeloid lineage, a process called myelopoiesis. When this process is uncontrolled, it can lead to AML.”

In healthy blood stem cells, normal GATA-2 expression is carefully balanced to activate a suite of genes that direct cell development of diverse blood cell types, including those of the myeloid and erythroid lineages. Previous studies of AML-associated disease mutations in GATA-2 found that the mutations reduced GATA-2 function in certain contexts, which led to the paradigm that insufficient GATA-2 levels can lead to acute myeloid leukemia.

“In this study, we wanted to understand in detail how GATA-2 disease mutations affect the protein function in cells,” Bresnick said. “We developed a new system to study how normal and mutant forms of GATA-2 function to control genes and cellular differentiation using ‘primary’ or normal cells.”

The new system Bresnick and his colleagues developed starts with blood precursor cells from GATA-2-deficient mice, which express around 70 percent less GATA-2 than normal cells and do not develop the full repertoire of cell types. Next, they added back a GATA-2 gene – either the normal, wild type version or a disease mutant version – to these cells, and tweaked their levels so that these cells had the same amounts of normal or mutant GATA-2 proteins. Then, they looked to see what changed.

The scientists measured how many cells developed along either the myeloid or erythroid pathways. As predicted, normal GATA-2 stimulated the development of both cell types. However, cells containing the GATA-2 mutant were heavily skewed toward the myeloid type, essentially making no erythroid cells. They also measured expression of GATA-2 target genes. While normal GATA-2 targeted the entire set of genes, mutant GATA-2 preferentially targeted genes favoring myeloid development.

“The serendipitous discovery was that certain disease mutants were actually more active than wild type GATA-2 – though only in the myeloid-specific contexts,” Bresnick said. “These results provide evidence to support a new paradigm in which GATA-2 deficiency does not fully explain the disease mechanism.”

This study, Bresnick added, provided evidence that some GATA-2 mutants have a gain of function at certain genes in the genome, and a loss of function at others. It is these changes that corrupt the genetic network that creates a predisposition to myelodysplastic syndromes (MDS) and acute myeloid leukemia.

“By knowing the molecular actions of these disease mutants within the complete genome, we can establish a strong foundation to explain the disease mechanism, as a prerequisite to rational drug design,” Bresnick said.