When a key gene in blood cell development, GATA-2, is mutated, it causes a predisposition to the development of acute myeloid leukemia (AML), and the changes in GATA-2 were believed to diminish its protein function.
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.
This study was supported in part by grants from the National Institutes of Health (DK68634), The Midwest Athletes Against Childhood Cancer (MACC) fund, the Evan MDS Foundation, the UW Carbone Cancer Center Support Grant P30 CA014520 and the UW Carbone Leukemia Philanthropic Fund.