Involving of the cytoplasmic region of leukemia inhibitory factor receptor alpha subunit, IL-6 related signal transducer-gp130 or fas death domain for MAPK p42/44 activation in HL-60 cell with LIF or anti-Fas IgG

Leukemia inhibitory factor receptor α-chain: a potential method for acute promyeloid leukemia therapy

Leukemia inhibitory factor (LIF) affects multiple types of leukemia cells in vitro through its functional receptor LIFR, which comprises a complex of the LIFR α-chain (LIFRα) and gp130. Researchers have recently observed that the C-terminus of the LIFRα cytoplasmic domain contains as many conserved YXXQ motifs as gp130 (C-terminal triple YXXQ motifs, LIFRα-CT3), whose free structure has been shown to be capable of activating STAT3 phosphorylation in the cytoplasm and consequently activating STAT3-related downstream molecules in the nucleus. This process can induce pathological acute myeloid leukemia (AML) or acute promyeloid leukemia (APL) cells to differentiate into mature granulocytes, simulating the LIF-related differential cascade. This process reduces or inhibits the side effects caused by toxic all-trans retinoid acid (ATRA), which has long been used as a fundamental medication for treating AML/APL in clinical practice despite its related high relapse rate. Therefore, we believe that it is possible to maximize the beneficial effects of LIF by enriching LIFRα-CT3 in AML/APL cell cytoplasm. The aims of this work were to enrich LIFRα-specific motifs in leukemia cells using molecular biological methods and evaluate the use of membrane-permeable polypeptides as a novel possible AML/APL therapy in combination with or independent of ATRA-based chemotherapy.

Secretory TAT-peptide-mediated protein transduction of LIF receptor α-chain distal cytoplasmic motifs into human myeloid HL-60 cells

The distal cytoplasmic motifs of leukemia inhibitory factor receptor α-chain (LIFRα-CT3) can independently induce intracellular myeloid differentiation in acute myeloid leukemia (AML) cells by gene transfection; however, there are significant limitations in the potential clinical use of these motifs due to liposome-derived genetic modifications. To produce a potentially therapeutic LIFRα-CT3 with cell-permeable activity, we constructed a eukaryotic expression pcDNA3.0-TAT-CT3-cMyc plasmid with a signal peptide (ss) inserted into the N-terminal that codes for an ss-TAT-CT3-cMyc fusion protein. The stable transfection of Chinese hamster ovary (CHO) cells via this vector and subsequent selection by Geneticin resulted in cell lines that express and secrete TAT-CT3-cMyc. The spent medium of pcDNA3.0-TAT-CT3-cMyc-transfected CHO cells could be purified using a cMyc-epitope-tag agarose affinity chromatography column and could be detected via SDS-PAGE, with antibodies against cMyc-tag. The direct administration of TAT-CT3-cMyc to HL-60 cell culture media caused the enrichment of CT3-cMyc in the cytoplasm and nucleus within 30 min and led to a significant reduction of viable cells (P < 0.05) 8 h after exposure. The advantages of using this mammalian expression system include the ease of generating TAT fusion proteins that are adequately transcripted and the potential for a sustained production of such proteins in vitro for future AML therapy.

Molecular analysis of signaling events mediated by the cytoplasmic domain of leukemia inhibitory factor receptor alpha subunit

A chimeric receptor (130/190) containing the cytoplasmic region of leukemia inhibitory factor receptor alpha subunit (LIFRalpha, or gp190) and the extracellular transmembrane region of gp130 was generated. Expressed of the 130/190 chimera in HL-60 cells to induced the homodimerization of the cytoplasmic domains (190cyt-190cyt) with whole LIFRalpha subunit on HL-60 cells in response to LIF. Expression and activation of the signal transducer and activator of transcription factor-3 (Stat3) and inhibition of leukemia cell proliferation were evaluated in cells transfected with this chimeric molecule. Increased tyrosyl phosphorylation of Stat3 at Tyr705 was detected after 10 min LIF treatment in cells transfected with either the 130/190 or the wild type receptor. Cell proliferation was decreased upon LIF treatment in both cell types. However, expression of the C-terminal region of the cytoplasmic region of LIFRalpha subunit (190CT) in HL-60 cells resulted in lower levels of Stat3 phosphorylation induction by LIF and cell proliferation was unaffected. Immunohistochemical staining indicated an inverse correlation between Cdc25B expression and the levels of phospho-Stat3 in 190CT and 130/190 cells. Expression of CD15, a cell differentiation marker, was lower in 190CT than in 130/190 cells. Together, these results suggest that homodimerization of the 190 cytoplasmic region promotes the Tyr 705 phosphorylation, which correlates with the inhibition of proliferation and stimulation of differentiation in HL-60 cells. Our results also suggest a signal link between Stat3 and Cdc25B.