The gene fragment encoding the 20-152aa of human IL3 is co-expressed with the C-terminal 10xHis-tag gene in mammalian cells via a vector. The resulting product is the recombinant human IL3 protein. The recombinant human IL3 protein is over 95% pure as determined by SDS-PAGE. The endotoxin level is less than 1.0 EU/ug of human IL3, as measured in a chromogenic LAL assay. The bioactivity of this recombinant IL3 protein is measured by the dose-dependent stimulation of the proliferation of human TF-1 erythroleukemic cells. The ED50 is 0.3149 to 1.023 ng/mL.
Human IL3 is a crucial cytokine involved in the regulation of hematopoiesis. IL3 is characterized by two conserved asparagine residues that allow for potential N-linked glycosylation, which is important for its biological activity and stability [1]. IL3 plays a significant role in promoting the proliferation and differentiation of various hematopoietic progenitor cells, including those that develop into erythrocytes, granulocytes, monocytes, megakaryocytes, and mast cells [1][2].
The biological function of IL3 is mediated through its interaction with the IL3R, which is composed of an alpha subunit (IL3Rα) and a common beta subunit (βc). This receptor complex is critical for initiating signaling pathways that lead to cell survival, differentiation, and proliferation [3]. Notably, IL3Rα is often overexpressed in various leukemic cells, particularly in acute myeloid leukemia (AML), where it is associated with poor prognosis [3]. The engagement of IL3R by IL3 activates downstream signaling cascades, including those involving protein kinase C and tyrosine kinases, which are essential for the growth and survival of hematopoietic cells [4].
Research has also indicated that polymorphisms in the IL3 gene can influence individual susceptibility to diseases such as Graves' disease, highlighting the cytokine's role beyond hematopoiesis in immune regulation [5]. Variants of IL3, such as those differing at amino acid position 8, have been shown to exhibit varying potencies in stimulating immune responses, which further underscores the importance of IL3 in both hematopoietic and immune functions [5].
Moreover, IL3 has been explored in therapeutic contexts, particularly in the development of recombinant fusion proteins that combine IL3 with diphtheria toxin. These constructs have shown promise in selectively targeting and killing leukemic cells while sparing normal hematopoietic progenitors, indicating a potential avenue for targeted cancer therapies [6][7]. The specificity of IL3 for its receptor and its role in promoting the survival of neoplastic stem cells make it a significant target for therapeutic interventions in hematological malignancies [7].
References:
[1] N. Quy, D. Khoa, D. Huong, H. Li, & T. Hai. Purification of recombinant human interleukin-3 expressed as inclusion bodies in <i>escherichi coli</i>, Academia Journal of Biology, vol. 43, no. 1, 2021. https://doi.org/10.15625/2615-9023/13973
[2] A. Nitsche, I. Junghahn, S. Thulke, J. Aumann, A. Radonić, I. Fichtner, et al. Interleukin‐3 promotes proliferation and differentiation of human hematopoietic stem cells but reduces their repopulation potential in nod/scid mice, The International Journal of Cell Cloning, vol. 21, no. 2, p. 236-244, 2003. https://doi.org/10.1634/stemcells.21-2-236
[3] T. Hercus, S. Broughton, M. Hardy, T. Nero, N. Wilson, M. Parker, et al. Unexpected mechanisms of action for a cytokine receptor-blocking antibody, Molecular & Cellular Oncology, vol. 1, no. 4, p. e969129, 2014. https://doi.org/10.4161/23288604.2014.969129
[4] Y. Jiang, F. Prósper, & C. Verfaillie. Opposing effects of engagement of integrins and stimulation of cytokine receptors on cell cycle progression of normal human hematopoietic progenitors, Blood, vol. 95, no. 3, p. 846-854, 2000. https://doi.org/10.1182/blood.v95.3.846.003k31_846_854
[5] X. Chu, C. Dong, L. Rong, L. Sun, Z. Wang, Y. Dong, et al. Polymorphisms in the interleukin 3 gene show strong association with susceptibility to graves’ disease in chinese population, Genes and Immunity, vol. 10, no. 3, p. 260-266, 2009. https://doi.org/10.1038/gene.2009.3
[6] A. Frankel, J. McCubrey, M. Miller, S. Delatte, J. Ramage, M. Kiser, et al. Diphtheria toxin fused to human interleukin-3 is toxic to blasts from patients with myeloid leukemias, Leukemia, vol. 14, no. 4, p. 576-585, 2000. https://doi.org/10.1038/sj.leu.2401743
[7] D. Hogge, L. Yalcintepe, S. Wong, B. Gerhard, & A. Frankel. Variant diphtheria toxin-interleukin-3 fusion proteins with increased receptor affinity have enhanced cytotoxicity against acute myeloid leukemia progenitors., Clinical Cancer Research, vol. 12, no. 4, p. 1284-1291, 2006. https://doi.org/10.1158/1078-0432.ccr-05-2070
