TET2-mediated epitranscriptomic regulation in leukemia microenvironment

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PROJECT SUMMARY: Background: Acute myeloid leukemia (AML) is one of the most aggressive types of hematopoietic malignancies with various genetic alterations. Ten-Eleven Translocation 2 (TET2), an enzyme involved in DNA demethylation, is deleted or mutated in 15-20% of AML patients. Those patients with TET2 deficiency are poorly responsive to currently available therapeutic regimens, leading to more adverse outcomes than patients with other AML subtypes. Thus, it is urgent to identify new therapeutic target(s) and develop novel effective approaches to treat TET2-deficient AMLs. Tet2 loss in mice facilitates the self-renewal of hematopoietic stem cells (HSCs) and leukemic stem/initiating cells (LSCs/LICs). The LSCs/LICs reside in a specialized microenvironment called “niche” in the bone marrow (BM) to support their survival and self-renewal. There are several critical gaps in our current knowledge of the molecular mechanism underlying LSC/LIC homing and of the role of TET2 deficiency in the BM microenvironment. Meanwhile, evidence is emerging to support a novel function for TET2-mediated oxidation of methyl-5-cytosine (m5C) in RNAs, including messenger RNA (mRNA). However, it is unknown whether and (if so) how TET2-mediated RNA m5C demethylation contributes to leukemogenesis. Our preliminary study showed that Tet2 deficiency stimulates the Tetraspanin 13 (Tspan13)/C-X-C motif chemokine receptor 4 (Cxcr4) axis to facilitate AML homing/migration into the BM microenvironment, giving rise to increased LSC/LIC self-renewal and fast leukemogenesis in vivo. Tet2 deficiency-mediated increase of mRNA m5C modification in Tspan13 is recognized by Y-box binding protein 1 (YBX1), which in turn stabilizes Tspan13 transcript and increases its expression, thereby activating the Cxcr4 signaling. Pharmacological inhibition of CXCR4 suppresses LSC/LIC homing into the BM microenvironment and shows a synergistic effect with hypomethylating agents in killing TET2-deficient AMLs. These results lead to our central hypothesis that TET2-mediated mRNA m5C demethylation is involved in reprogramming BM microenvironment. Guided by strong preliminary data, we propose three Specific Aims to test our hypothesis: (1) Determine the definitive role of TET2 in the homing of LSCs/LICs into BM microenvironment; (2) Characterize the mRNA m5C-dependent and functionally essential targets of TET2 and decipher the molecular mechanisms underlying the role of TET2 in LSC/LIC homing and self-renewal; and (3) Assess the therapeutic potential of targeting the TET2/CXCR4 axis in high-risk TET2-deficient AMLs. Overall, our proposed studies will substantially advance our understanding of the fundamental biology of TET2-mediated epitranscriptomic changes in BM microenvironment and may result in the development of novel effective approaches to treat AMLs with TET2 deficiency. Thus, our project is of high novelty and significance in both basic research and translational medicine.