title: Distinct MAPK signaling pathways, p21 up-regulation and caspase-mediated p21 cleavage establishes the fate of U937 cells exposed to 3-hydrogenkwadaphnin: differentiation versus apoptosis.
abstract: Despite the depth of knowledge concerning the pathogenesis of acute myeloblastic leukemia (AML), long-term survival remains unresolved. Therefore, new agents that act more selectively and more potently are required. In that line, we have recently characterized a novel diterpene ester, called 3-hydrogenkwadaphnin (3-HK), with capability to induce both differentiation and apoptosis in various leukemia cell lines. These effects of 3-HK were mediated through inhibition of inosine 5'-monophosphate dehydrogenase, a selective up-regulated enzyme in cancerous cells, especially leukemia. However, it remains elusive to understand how cells display different fates in response to 3-HK. Here, we report the distinct molecular signaling pathways involved in forcing of 3-HK-treated U937 cells to undergo differentiation and apoptosis. After 3-HK (15 nM) treatment, a portion of U937 cells adhered to the culture plates and showed macrophage criteria while others remained in suspension and underwent apoptosis. The differentiated cells arrested in G(0)/G(1) phase of cell cycle and showed early activation of ERK1/2 pathway (3 h) along with ERK-dependent p21(Cip/WAF1) (p21) up-regulation and expression of p27(Kip1) and Bcl-2. In contrast, the suspension cells underwent apoptosis through Fas/FasL and mitochondrial pathways. The occurrence of apoptosis in these cells were accompanied with caspase-8-mediated p21 cleavage and delayed activation (24 h) of JNK1/2 and p38 MAPK. Taken together, these results suggest that distinct signaling pathways play a pivotal role in fates of drug-treated leukemia cells, thus this may pave some novel therapeutical utilities.
authors.affiliation: Institute of Biochemistry and Biophysics, P. O. Box 13145-1384 University of Tehran, Tehran, Iran.
authors.forename: Mohammad Amin
authors.initials: MA
authors.lastname: Moosavi
authors.forename: Razieh
authors.initials: R
authors.lastname: Yazdanparast
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004224:Diterpenes / Q000494:pharmacology*; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D020298:U937 Cells; D015854:Up-Regulation
chemical_list: C505417:3-hydrogenkwadaphnin; D061945:Caspase Inhibitors; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004224:Diterpenes; D020929:Mitogen-Activated Protein Kinase Kinases; D020169:Caspases