Reactive Oxygen Species and Redox-induced Programmed Cell Death Due to MK 886: Cells (“Soil”) “Trump” Agent (“Seed”)

Abstract

Micromolar concentrations of the five-lipoxygenase inhibitor, MK 886 induce a “type 1” (apoptotic, extrinsic, death domain, receptor-dependent, caspase-positive) form of programmed cell death in Bcl-2-positive U937 human monoblastoid and HL-60 myeloid leukemia cells. A “type 2” (intrinsic, mitochondria-dependent, autophagic, in some examples caspase-negative (Panc-1)) form is induced in Panc-1 pancreatic and PC3 prostate cell lines. The latter two lines from epithelial-derived solid human cancers are Bcl-2-negative. Micromolar MK 886 induces an acute rise in Ca²⁺ in washed, Ca²⁺-poor U937 and HL60 cells in Ca²⁺ and Mg²⁺-free Hank's buffer. In U937 cells, much of the increase, or more properly redistribution, is nuclear in location (HL-60 not tested). No MK-886-induced acute Ca²⁺ increase developed in Panc-1 or PC3 cells. Bcl-2-positive HeLa cervical cancer cells exhibited an acute MK 886-induced increase in Ca²⁺. In the U937, PC3 and Panc-1 cells examined, MK-886 rapidly increased oxidative stress and decreased mitochondrial membrane potential, indicating that neither event is directly determinative for the altered distribution of Ca²⁺ or the form of PCD observed. Inhibition of increased U937 Ca²⁺ by the anti-oxidant, N-acetyl-L-cysteine, the effects of inhibitors of mitochondrial function including antimycin A, atractyloside, cyclosporin A, the L/N channel blocker loperamide, the intracellular chelator BAPTA and 2 agents, HA-14 and 3-methyl-antimycin A3 that impair Bcl-2 function further define these events. These differences in the Ca²⁺ response and possibly also the form of PCD that results may depend upon the presence of Bcl-2 or a related protein participating in a juxta-nuclear / nuclear Ca²⁺ ion channel. The role of mitochondria, the mechanism by which increased oxidative stress initiates the rapid release of Ca²⁺ from intracellular, possibly juxta-nuclear / nuclear sites or its redistribution to U937 Ca²⁺ nuclei, and whether this “signal” or possibly even ROS themselves mandate the type of PCD observed, presumably by differential modulation of transcription, remain to be determined. Lastly, these results demonstrate that, as might be expected, “soil” (cell type) trumps “seed” (inciting agent)”.