Role of Heterochromatin Epigenetic Factors in CML

PUBLIC ABSTRACT

Chronic myelogeneous leukemia (CML) and other myeloproliferative disorders initially develop through the chronic phase, when immature white blood cells (myeloid progenitors) excessively proliferate, but then undergo complete differentiation and become mature blood cells. Most existing therapies for such diseases are aimed at limiting the excessive proliferation of myeloid progenitors. Many cases of CML in its chronic stage are successfully treated with Gleevec making this disease a model system for anti-cancer therapy. However, about 10% of CML cases and most other myeloproliferative disorders are less responsive to the proliferation-limiting therapy. In such cases, the affected blood cells lose the ability to mature into normal differentiated blood cells and the chronic diseases transform into accelerated forms, blast crises, or acute secondary leukemias. When this happens, many immature cells overpopulate the blood, impair the normal blood functions, and cause death. For therapy-resistant CML and other closely related myeloproliferative disorders, the molecular processes that trigger the incomplete differentiation and the disease acceleration are not known. These facts underscore the need for research aimed at understanding the molecular and genetic changes that happen during the chronic phase of the disease in excessively proliferating myeloid cells and may be employed to predict and/or reverse the incomplete cell differentiation leading to the disease acceleration and death. Therefore, the general goal of this proposal is to improve the prognosis of the transition from a chronic to accelerated form of CML and other chronic myeloproliferative disorders and to understand the molecular basis of the incomplete myeloid differentiation resulting from CML in order to design new therapies capable of preventing the disease acceleration and death.

To reach this goal, we propose to study the role of heterochromatin factors in normal myeloid differentiation and CML. Heterochromatin is the complex of DNA with special proteins that make the DNA very condensed. This DNA includes repressed inactive genes that do not make RNA in the given cell type. For many years, this chromatin fraction was thought to be either "junk" or a "collector's item." However, it has become increasingly clear that heterochromatin is directly involved in repression of genes causing cell proliferation and cancer and its defects lead to unregulated cell proliferation, incomplete cell maturation, and death. This proposal is based on our innovative concept that a dramatic change in heterochromatin proteins occurs during normal blood cell differentiation and that this transition is impaired in cells from accelerated phase and blast crisis of CML and acute leukemia derived from myeloproliferative disorders. We found that a special protein, HP1, controlling heterochromatin formation in normal proliferating cell and myeloid progenitors, is completely absent from mature blood cells while another heterochromatin-associated protein, MNEI, that is absent from immature myeloid progenitors, accumulates in mature white blood cells. We further found that these two proteins co-exist only in the blood cells from patients with accelerated phase and blast crisis CML, and secondary forms of acute leukemias derived from chronic myeloproliferative disorders. In addition, MNEI from mature blood cells of chronic CML patients shows a significant accumulation of an altered molecular weight form absent from normal white blood cells. Based on these results, we hypothesized that the molecular alteration of MNEI and its interference with HP1 may contribute to development of accelerated phase and blast crisis in CML. To test and further develop this hypothesis here we propose (a) to determine the exact structure of the altered molecular isoform of MNEI, which are expressed in the blood of CML patients, and use this structure to design tools (specific antibodies) that will allow us to determine the particular location of the modified isoform in chromatin and its relationship with HP1 so that we can use this information to predict the disease acceleration and blastic transition; (b) co-express MNEI and HP1 in proliferating myeloid cells to determine the effect of their interference on myeloid differentiation, and chromatin condensation, and on expression of particular genes involved in normal differentiation. This information will allow us to design new therapies aimed at restoring the normal process of myeloid differentiation and prevent or reverse CML acceleration.

This work is expected to have both immediate and long-lasting impacts on CML treatment and prognostics. The immediate benefit of this work for CML treatment is that the heterochromatin factors will be validated as novel prognostic and diagnostic markers that can be used to predict the disease acceleration and accordingly optimize the treatment regimens. Furthermore, the knowledge of the structural alterations and the mechanism of interference of the heterochromatin factors will open the way to design new molecular drugs for accelerated CML and other forms of leukemia associated with incomplete myeloid differentiation.