IKAROS: from chromatin organization to transcriptional elongation control

IKAROS is a master regulator of cell fate determination in lymphoid and other hematopoietic cells. This transcription factor orchestrates the association of epigenetic regulators with chromatin, ensuring the expression pattern of target genes in a developmental and lineage-specific manner. Disruption of IKAROS function has been associated with the development of acute lymphocytic leukemia, lymphoma, chronic myeloid leukemia and immune disorders. Paradoxically, while IKAROS has been shown to be a tumor suppressor, it has also been identified as a key therapeutic target in the treatment of various forms of hematological malignancies, including multiple myeloma. Indeed, targeted proteolysis of IKAROS is associated with decreased proliferation and increased death of malignant cells. Although the molecular mechanisms have not been elucidated, the expression levels of IKAROS are variable during hematopoiesis and could therefore be a key determinant in explaining how its absence can have seemingly opposite effects. Mechanistically, IKAROS collaborates with a variety of proteins and complexes controlling chromatin organization at gene regulatory regions, including the Nucleosome Remodeling and Deacetylase complex, and may facilitate transcriptional repression or activation of specific genes. Several transcriptional regulatory functions of IKAROS have been proposed. An emerging mechanism of action involves the ability of IKAROS to promote gene repression or activation through its interaction with the RNA polymerase II machinery, which influences pausing and productive transcription at specific genes. This control appears to be influenced by IKAROS expression levels and isoform production. In here, we summarize the current state of knowledge about the biological roles and mechanisms by which IKAROS regulates gene expression. We highlight the dynamic regulation of this factor by post-translational modifications. Finally, potential avenues to explain how IKAROS destruction may be favorable in the treatment of certain hematological malignancies are also explored.

Automated summary

IKAROS is a crucial regulator involved in determining the fate of lymphoid and other hematopoietic cells. It plays a role in the association of epigenetic regulators with chromatin, ensuring the proper expression of target genes during development and lineage specification. Disruption of IKAROS function has been linked to the development of various blood malignancies and immune disorders. Interestingly, while IKAROS acts as a tumor suppressor, it is also considered a key therapeutic target for the treatment of hematological malignancies, including multiple myeloma. The mechanisms by which IKAROS functions are not fully understood, but it is known to interact with various proteins and complexes involved in chromatin organization and transcriptional regulation. IKAROS can promote gene repression or activation by interacting with the RNA polymerase II machinery. The expression levels and isoform production of IKAROS are variable and may play a role in the seemingly opposite effects of its absence. This review summarizes the current understanding of IKAROS' biological roles and mechanisms, with a focus on its post-translational modifications. Additionally, potential explanations for how IKAROS destruction may be beneficial in the treatment of certain hematological malignancies are explored.