m6A Modification Prevents Formation of Endogenous Double-Stranded RNAs and Deleterious Innate Immune Responses during Hematopoietic Development

M6 A modification: A mechanism for protecting hematopoietic development in mammals

N⁶ -methyladenosine (m⁶ A) is one of the most common internal modifications in messenger RNA, which is necessary for cell physiological activities. A recent study shows that during mammalian hematopoietic development, loss of m⁶ A modification leads to the aberrant production of double-stranded RNA, which results in the abnormal activation of innate immune response, and ultimately leads to hematopoietic failure. Accordingly, m⁶ A modification provide us an attractive direction for us to understand mammalian hematopoietic development and innate immune response.

The old and the new: DNA and RNA methylation in normal and malignant hematopoiesis

Whilst DNA cytosine methylation is the oldest and most well-studied epigenetic modification, basking in its glory days, it may be soon overshadowed by the new kid on the block: RNA adenosine methylation. This juxtaposition is indeed superficial, and a deep exploration toward the fundamental requirements for these essential epigenetic marks provides a clear perspective on their converging and synergistic roles. The recent discovery that both of these modifications are essential for preventing inappropriate activation of the intracellular innate immune responses to endogenous transcripts has provided a lot of interest in targeting them therapeutically as a means to improve cancer immunogenicity. Here we discuss the potential physiological function for DNA and RNA methylation in normal hematopoiesis and how these pervasive epigenetic marks are exploited in cancer, and provide suggestions for future research with a focus on leveraging this knowledge to uncover novel therapeutic targets.

The role of RNA epigenetic modification in normal and malignant hematopoiesis

Purpose of Review

RNA epigenetic modifications have been identified as novel, dynamic regulators of gene expression, with important impacts on stem cell fate decisions. Here, we examine the functions of RNA modifications, with a focus on N⁶-methyladenosine (m⁶A), in hematopoietic stem cells under normal conditions and in malignancy.

Recent Findings

The m⁶A RNA modification is a critical regulator of hematopoiesis. Disruption of different elements of the m⁶A machinery can skew the balance of self-renewal and differentiation in normal hematopoietic stem cells. The m⁶A reader, writer, and eraser proteins are also overexpressed in myeloid leukemia, and disruption of their function impairs leukemogenesis. RNA m⁶A modification governs important aspects of immune system function, including immune cell development, immune signaling, and recognition of RNA as foreign or self. In hematopoietic stem cells, endogenously derived double-stranded RNA can form in the absence of m⁶A, inducing deleterious inflammatory pathways which compromise stem cell function.

Summary

The RNA modification m⁶A exerts a variety of functions in normal hematopoietic stem cells as well as leukemic cells. Pharmacologic modulation of different elements of the m⁶A machinery provides a promising avenue for ex vivo expansion of hematopoietic stem cells in the transplant setting, as well as for leukemia therapy.