Dr. Casey Katerndahl joined the Department of Medicine in the Division of Oncology as an Instructor in June, 2020.
The long-term goal of Dr. Katerndahl’s research is to better define the molecular mechanisms that control the aberrant self-renewal and transformation of myeloid progenitor cells, and to use this information to improve therapy for acute myeloid leukemia (AML) patients. To achieve these goals, several well-characterized models of AML, such as the Ctsg-PML-RARA mouse model of acute promyelocytic leukemia (APL), combined with modern laboratory techniques such as single cell RNA sequencing and CRISPR-Cas9 genome editing are utilized. During Dr. Katerndahl’s post-doctoral training in Dr. Timothy Ley’s lab, he identified several candidate genes that are utilized by AML-initiating mutations to promote the disease. Now, these these candidate genes are being functionally validated, and the mechanisms by which these genes contribute to AML are being determined.
One of these candidates is the transcription factor GATA2, which has been found to be spontaneously mutated in the founding clone in 2 out of 16 mouse APLs screened by exome sequencing. This suggests that mutations in GATA2 promote the transformation of myeloid progenitor cells. Moreover, inherited mutations in the GATA2 gene cause the MonoMAC and Emberger Syndromes, pre-leukemic conditions that strongly increase the risk of developing MDS or AML. Somatic GATA2 mutations also occur in ~5 % of de novo AML patients, including those with APL. However, there is no current consensus on whether somatic mutations in GATA2 cause gain- or loss-of-function properties. GATA2 is highly expressed in normal CD34+ stem cells and is persistently expressed in several subtypes of AML including APL. By contrast, GATA2 expression is normally shut off by the promyelocyte stage of myeloid development. The team also found that myeloid progenitor cells from Ctsg-PML-RARA mice express higher levels of Gata2 than those from WT mice. Therefore, it was hypothesized that PML-RARA promotes and utilizes GATA2 expression to promote aberrant self-renewal and APL.
To test this prediction, the team generated PML-RARA x Cas9 mice. Targeting Gata2 with CRISPR-Cas9 guide RNAs in the bone marrow from PML-RARA x Cas9 mice surprisingly caused a 5 to 20-fold increase in serial replating efficiency, compared to control-targeted PML-RARA x Cas9 bone marrow. Digital sequencing and western blotting showed that biallelic loss-of-function mutations of Gata2 were selected for in these assays, with a complete deficiency of GATA2 protein in serially replated cells. To determine whether the accelerated replating phenotype in Gata2-deficient, PML-RARA-expressing cells could be reversed, WT Gata2 expression was enforced, using MSCV-based retroviruses. The expression of WT Gata2 was strongly selected against in these assays, whereas expression of the AML-associated R362G Gata2 was minimally selected against.
Finally, it was found that Gata2 deficiency in PML-RARA-expressing bone marrow cells also decreased APL latency and increased penetrance. Together, these data suggest that GATA2 unexpectedly acts as a tumor suppressor in myeloid progenitor cells, and that AML-associated GATA2 mutations contribute to AML progression by reducing the function of GATA2.
Now, single cell sequencing techniques are being used to elucidate the molecular mechanisms by which GATA2 controls the transformation of myeloid progenitor cells.