Interleukin-3 (IL3) is a cytokine that regulates blood-cell production by controlling the production, differentiation and function of granulocytes and macrophages [, ]. The protein, which exists in vivo as a monomer, is produced in activated T-cells and mast cells [, ], and is activated by the cleavage of an N-terminal signal sequence [].IL3 is produced by T-lymphocytes and T-lymphomas only after stimulation with antigens, mitogens, or chemical activators such as phorbol esters. However, IL3 is constitutively expressed in the myelomonocytic leukaemia cell line WEHI-3B []. It is thought that the genetic change of the cell line to constitutive production of IL3 is the key event in development of this leukaemia [].
Nuclear factor interleukin-3-regulated protein (NFIL3, also known as E4BP4) was first identified as a transcriptional repressor capable of binding an activating transcription factor (ATF) DNA consensus sequence site in the adenovirus E4 promoter []. Later, it was independently identified as a transactivator of the IL3 promoter in human T cells [].E4BP4 is involved in a several biological processes, including transcriptional control of the circadian clock, neuron growth and survival, osteoblast function, and regulation of ovulation []. It is essential for the development of NK cells and CD8alpha(+) conventional dendritic cells, and is also involved in macrophage activation, polarisation of CD4(+) T cell responses and B cell class switching to IgE [].
