Commonly Dysregulated Genes in Murine Acute Promyelocytic Leukemia (APL) Cells.

To identify genes that are commonly dysregulated in a murine model of acute promyelocytic leukemia (mice expressing PML-RARa under control of the murine cathepsin G locus), we first defined gene expression patterns during normal murine myeloid development; serial gene expression profiling studies were performed with primary murine hematopoietic progenitors that were induced to undergo myeloid maturation in vitro with G-CSF. This system provided a method for obtaining highly enriched populations of murine myeloid cells at well-defined stages of differentiation: stem and progenitor cells were enriched on Day 0, promyelocytes were the predominant cell in culture on Day 2–3, mid-myeloid cells were most abundant on Day 4–5, and terminally differentiated myeloid cells were enriched on Day 6–7. These stages were validated using well-characterized “marker” genes for each developmental stage. Many genes were reproducibly expressed in restricted developmental “windows”, suggesting a structured hierarchy of expression that is relevant for the induction of developmental fates and/or differentiated cell functions. Some genes relevant for the pathogenesis of acute myelogenous leukemia (AML) also showed dynamic changes during myeloid differentiation.

We compared the normal myeloid developmental transcriptome to that of APL cells derived from the mCG-PML-RARa knock-in mice. While many promyelocyte-specific genes were highly expressed in all APL samples, 116 genes were reproducibly dysregulated in many independent APL samples. These included 4 classes:

1. genes that were highly expressed in murine APL cells but not in normal myeloid cells at any stage of development,

2. genes normally expressed only in early hematopoietic progenitors (d0) but abnormally expressed in APL cells,

3. genes normally expressed only in late myeloid cells (d7) but also expressed in APL cells, and

4. genes normally expressed in promyelocytes (d2) but not in APL cells.

Many of these dysregulated genes had previously been linked to oncogenic transformation, including Fos, Jun, Egr-1, TNF, and VCAM-1. However, we found that this set of commonly dysregulated genes was expressed normally in preleukemic promyelocytes from the same mouse model, suggesting that dysregulation occurs as a “downstream” event during disease progression. These studies suggest that the genetic events that lead to APL progression may converge on common pathways that are important for leukemia pathogenesis.