Abstract
The gene regulatory functions of the human IL-2 receptor (IL-2R) were reconstituted in transiently transfected hepatoma cells. The combination of IL-2R beta and -gamma mediated a strong stimulation via the cytokine response element of the alpha 1-acid glycoprotein gene and the hematopoietin receptor response element, but none via the IL-6 response element or the sis-inducible element. IL-2R alpha enhanced 10-fold the sensitivity of the IL-2R beta.gamma complex to respond to IL-2 or IL-15, but did not modify the specificity or the magnitude of maximal gene regulation. A homodimerizing chimeric receptor G-CSFR-IL-2R beta could mimic the IL-2R action. The IL-2R-mediated gene regulation was similar to that seen with receptors for IL-4 and IL-7, but differed from that for IL-6 type cytokines, thrombopoietin, erythropoietin, and growth hormone. The activation of STAT proteins by the IL-2R was assessed in transfected L-cells and COS-1 cells. Although IL-2R subunits were highly expressed in these cells, no STAT protein activation was detectable. Transient overexpression of JAK3 was unable to change the signaling specificity of the hematopoietin receptors in rat hepatoma, L-, and COS cells, but established a prominent activation of the IL-6 response elements by the IL-2R and IL-4R in HepG2 cells. The data support the model that the IL-2R and related hematopoietin receptors produce at least two separate signals which control gene expression.
Highlights
The gene regulatory functions of the human IL-2 receptor (IL-2R) were reconstituted in transiently transfected hepatoma cells
The IL-2R-mediated gene regulation was similar to that seen with receptors for IL-4 and IL-7, but differed from that for IL-6 type cytokines, thrombopoietin, erythropoietin, and growth hormone
A modulating effect on transcription of early growth response genes, such as e-fos, c-jun, junB, and c-myc, has been demonstrated for several of these receptors [10, 16,17,18,19,20], the function of hematopoietin receptors, whose expression has been maintained during the course of cell differentiation, appears to involve the transcriptional control of differentiated genes such as neuropeptide genes by LIF and CNTF in neuronal cells [21, 22], genes for myeloperoxidase, elastase, and G-CSFR by G-CSF in granulocytes [18, 23,24,25], cytokine genes by IL-2, IL-15, and IL-12 in NK cells [24,25,26], or acute phase plasma protein genes by IL-6-type cytokines in hepatic cells [27]
Summary
Cells and Cell Treatments-Receptor functions were determined in rat hepatoma H-35 cells (subclonalline of clone T-7-18; Ref. 46), human HepG2 cells [47], COS-1 cells and mouse 1(tk~) cells. The cells were cultured in Dulbecco's modified Eagle's medium (H-35 and L-cells) or minimal essential medium (HepG2 and COS-1 cells) containing 10% fetal calf serum, penicillin, streptomycin, and gentamycin. For comparison of SIF activation, we used CTLL-2 cells which were cultured in RPMI containing 10% fetal calf serum supplemented with 250 units/ml IL-2. All cytokine treatments occurred in serum-free minimal essential medium. The chimeric receptor constructs contained the extracellular domain ofG-CSFR and the transmembrane and cytoplasmic domains of the following receptors: full-length or 150-amino acid residues of human LIFR (G-CSFR-LIFR and G-CSFR-LIFR[150]) [43], gp130 (G-CSFR-gp130) [43], c-mpl (G-CSFR-MPL) [56], and IL-2R-y (G-CSFR-IL-2R-y).. Cytokine signal pAGP(3 x DRE)-GRE-CAT pAGP(4 x CytRE)-SV-CAT pAGP(4 x IL-lRE)-SV-CAT p(4 x SIE)-CAT
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