Johnson Thomas

Bacterial proteins as potential drugs in the treatment of leukemia.

Azurin and Laz are bacterial proteins that have been shown to exert anticancer effects against a variety of solid tumors. Their effects on liquid cancers have never been studied. We now show that they are also effective against liquid-borne cancers such as leukemia. Azurin and Laz can each enter in two leukemia cell lines but Laz exerts a greater cytotoxic effect on both K562 and HL60 cells, while having little effect on peripheral blood mononuclear cells, where they have very limited entry. In addition to Azurin and Laz, we have recently identified another protein, Pa-CARD, from Pseudomonas aeruginosa that carries a caspase recruitment domain (CARD)-like domain. This CARD domain polypeptide, called Pa-CARD, demonstrates cytotoxic activity against leukemia cells. In the leukemia cell lines, HL60 and K562, the anticancer activity of Laz and Pa-CARD is mediated through cell cycle arrest at the G2/M phase involving the Wee1 protein stabilization and the depletion of phosphorylated AKT-Ser-473, the active form of a serine/threonine kinase that is often dysregulated in many cancer types.

Anthrax Lethal Factor Activates K+ Channels To Induce IL-1β Secretion in Macrophages

Anthrax lethal toxin (LeTx) is a virulence factor of Bacilillus anthracis that is a bivalent toxin, containing lethal factor (LF) and protective Ag proteins, which causes cytotoxicity and altered macrophage function. LeTx exposure results in early K+ efflux from macrophages associated with caspase-1 activation and increased IL-1β release. The mechanism of this toxin-induced K+ efflux is unknown. The goals of the current study were to determine whether LeTx-induced K+ efflux from macrophages is mediated by toxin effects on specific K+ channels and whether altered K+-channel activity is involved in LeTx-induced IL-1β release. Exposure of macrophages to LeTx induced a significant increase in the activities of two types of K+ channels that have been identified in mouse macrophages: Ba2+-sensitive inwardly rectifying K+ (Kir) channels and 4-aminopyridine–sensitive outwardly rectifying voltage-gated K+ (Kv) channels. LeTx enhancement of both Kir and Kv required the proteolytic activity of LF, because exposure of macrophages to a mutant LF-protein (LFE687C) combined with protective Ag protein had no effect on the currents. Furthermore, blocking Kir and Kv channels significantly decreased LeTx-induced release of IL-1β. In addition, retroviral transduction of macrophages with wild-type Kir enhanced LeTx-induced release of IL-1β, whereas transduction of dominant-negative Kir blocked LeTx-induced release of IL-1β. Activation of caspase-1 was not required for LeTx-induced activation of either of the K+ channels. These data indicate that a major mechanism through which LeTx stimulates macrophages to release IL-1β involves an LF-protease effect that enhances Kir and Kv channel function during toxin stimulation.