DNA-binding protein Ikaros also known as Ikaros family zinc finger protein 1 is a protein that in humans is encoded by the IKZF1 gene. [5] [6] [7]
Ikaros is a transcription factor that is encoded by the IKZF genes of the Ikaros family zinc finger group. Zinc finger is a small structural motif of protein that allows protein binding to DNA or RNA molecule that is characterized by the coordination of one or more zinc ions (Zn2+) in order to stabilize the fold.
Ikaros displays crucial functions in the hematopoietic system and is a known regulator of immune cells development, mainly in early B cells, CD4+ T cells. Its dysfunction has been linked to the development of chronic lymphocytic leukemia. [8] [9] In particular, Ikaros has been found in recent years to be a major tumor suppressor involved in human B-cell acute lymphoblastic leukemia [8] and that it also has a part in the differentiation and function of individual T helper cells. [10]
Ikaros also has a role during the later stages of B cell development during VDJ recombination in switch class of the antibody isotypes and expression of the B cell receptor. [11]
In Ikaros knockout mice, T cells but not B cells are generated late in mouse development due to late compensatory expression of the related gene Aiolos (IKZF3). [12] Ikaros point mutant mice are embryonic lethal due to anemia; they have severe defects in terminal erythrocyte and granulocyte differentiation, and excessive macrophage formation. [13] SNPs located near the 3' region of IKZF1 in humans have been linked to susceptibility to childhood acute lymphoblastic leukemia (ALL) [14] as well as type 1 diabetes. [15] The two effects appear to be in opposite directions, with the allele marking susceptibility to ALL protecting from T1D and vice versa. [15]
Further evidence shows that Ikaros regulates the development of medullary thymic epithelial cells (mTECs). Conditional deletion of Ikzf1 in thymic epithelial cells by Foxn1-Cre in mice, results in the dysregulation of various mTEC subsets, including the loss of Aire+ mTECs. The loss of Aire (Autoimmune regulator) expressing mTECs also causes global loss of tissue restricted antigens (TRAs) and Aire-dependent mimetic cell populations, with the loss of TRAs eventually leading to breakdown of immune tolerance. [16]
The Ikaros Zinc Finger (IkZF) family of transcription factors are known regulators of hematopoietic cell development and many immune cells including that of CD4+ T cells.
The IkZF family consists of five members: Ikaros (encoded by the gene Ikzf1), Helios ( Ikzf2 ), Aiolos ( Ikzf3 ), Eos ( Ikzf4 ), and Pegasus ( Ikzf5 ). These factors contain N-terminal zinc finger (ZF) domains, which are responsible for mediating direct interactions with DNA, and C-terminal ZFs, which facilitate homo- and heterodimerization between IkZF family members. [17]
IKZF1 is upregulated in granulocytes, B cells, CD4 and CD8 T cells, and NK cells, and downregulated in erythroblasts, megakaryocytes and monocytes. [18]
The mutation in the IKZF1 gene can cause dysfunction of the Ikaros transcription factor. The dysfunction affects expression in B cells that can lead to deregulation of the BCR signaling during B cell development and is associated with B cell transformation. The deregulation then can result in low proliferation rate and increased apoptosis of the B cells. The deregulation may be related with lymphoproliferative disorders and different forms of leukemia. [19]
IKZF1 has been shown to interact with:
Histone deacetylase 1 (HDAC1) is an enzyme that in humans is encoded by the HDAC1 gene.
Histone deacetylase 2 (HDAC2) is an enzyme that in humans is encoded by the HDAC2 gene. It belongs to the histone deacetylase class of enzymes responsible for the removal of acetyl groups from lysine residues at the N-terminal region of the core histones. As such, it plays an important role in gene expression by facilitating the formation of transcription repressor complexes and for this reason is often considered an important target for cancer therapy.
Bcl-6 is a protein that in humans is encoded by the BCL6 gene. BCL6 is a master transcription factor for regulation of T follicular helper cells proliferation. BCL6 has three evolutionary conserved structural domains. The interaction of these domains with corepressors allows for germinal center development and leads to B cell proliferation.
Paired amphipathic helix protein Sin3a is a protein that in humans is encoded by the SIN3A gene.
Zinc finger and BTB domain-containing protein 16 is a protein that in humans is encoded by the ZBTB16 gene.
Metastasis-associated protein MTA1 is a protein that in humans is encoded by the MTA1 gene. MTA1 is the founding member of the MTA family of genes. MTA1 is primarily localized in the nucleus but also found to be distributed in the extra-nuclear compartments. MTA1 is a component of several chromatin remodeling complexes including the nucleosome remodeling and deacetylation complex (NuRD). MTA1 regulates gene expression by functioning as a coregulator to integrate DNA-interacting factors to gene activity. MTA1 participates in physiological functions in the normal and cancer cells. MTA1 is one of the most upregulated proteins in human cancer and associates with cancer progression, aggressive phenotypes, and poor prognosis of cancer patients.
Histone-lysine N-methyltransferase 2A, also known as acute lymphoblastic leukemia 1 (ALL-1), myeloid/lymphoid or mixed-lineage leukemia1 (MLL1), or zinc finger protein HRX (HRX), is an enzyme that in humans is encoded by the KMT2A gene.
C-terminal-binding protein 1 also known as CtBP1 is a protein that in humans is encoded by the CTBP1 gene. CtBP1 is one of two CtBP proteins, the other protein being CtBP2.
YY1 is a transcriptional repressor protein in humans that is encoded by the YY1 gene.
Histone deacetylase 5 is an enzyme that in humans is encoded by the HDAC5 gene.
Histone deacetylase 9 is an enzyme that in humans is encoded by the HDAC9 gene.
Interferon regulatory factor 4 (IRF4) also known as MUM1 is a protein that in humans is encoded by the IRF4 gene. IRF4 functions as a key regulatory transcription factor in the development of human immune cells. The expression of IRF4 is essential for the differentiation of T lymphocytes and B lymphocytes as well as certain myeloid cells. Dysregulation of the IRF4 gene can result in IRF4 functioning either as an oncogene or a tumor-suppressor, depending on the context of the modification.
Histone deacetylase 7 is an enzyme that in humans is encoded by the HDAC7 gene.
Chromodomain-helicase-DNA-binding protein 4 is an enzyme that in humans is encoded by the CHD4 gene. CHD4 is the core nucleosome-remodelling component of the Nucleosome Remodelling and Deacetylase (NuRD) complex.
Paired amphipathic helix protein Sin3b is a protein that in humans is encoded by the SIN3B gene.
Zinc finger protein Aiolos also known as Ikaros family zinc finger protein 3 is a protein that in humans is encoded by the IKZF3 gene.
Zinc finger and BTB domain-containing protein 7A is a protein that in humans is encoded by the ZBTB7A gene.
B-cell lymphoma/leukemia 11B is a protein that in humans is encoded by the BCL11B gene.
Zinc finger protein Helios is a protein that in humans is encoded by the IKZF2 gene. This protein is a member of Ikaros family of transcription factors.
Zinc finger protein Eos is a protein that in humans is encoded by the IKZF4 gene.