Role of NADPH oxidase in arsenic-induced reactive oxygen species formation and cytotoxicity in myeloid leukemia cells.

Arsenic has played a key medicinal role against a variety of ailments for several millennia, but during the past century its prominence has been displaced by modern therapeutics. Recently, attention has been drawn to arsenic by its dramatic clinical efficacy against acute promyelocytic leukemia. Although toxic reactive oxygen species (ROS) induced in cancer cells exposed to arsenic could mediate cancer cell death, how arsenic induces ROS remains undefined. Through the use of gene expression profiling, interference RNA, and genetically engineered cells, we report here that NADPH oxidase, an enzyme complex required for the normal antibacterial function of white blood cells, is the main target of arsenic-induced ROS production. Because NADPH oxidase enzyme activity can also be stimulated by phorbol myristate acetate, a synergism between arsenic and the clinically used phorbol myristate acetate analog, bryostatin 1, through enhanced ROS production can be expected. We show that this synergism exists, and that the use of very low doses of both arsenic and bryostatin 1 can effectively kill leukemic cells. Our findings pinpoint the arsenic target of ROS production and provide a conceptual basis for an anticancer regimen.

Identification and characterization of the novel centrosome-associated protein CCCAP.

We have cloned and characterized the cDNA, expression pattern, and subcellular localization of the human and murine orthologs of the centrosomal colon cancer autoantigen protein (CCCAP). We identified both the transcriptional start site of murine CCCAP (mCCCAP) and its TATA-less promoter within BAC genomic clones of the mCCCAP 5' region. The mCCCAP transcript is ubiquitously present in mouse tissues, but at very low copy number. The 2151 bp open reading frame of mCCCAP encodes an 83 kDa protein that possesses a large C-terminal coiled-coil domain, which is able to homo-oligomerize in the yeast 2-hybrid system. Endogenous mCCCAP localizes to the centrosomes of murine BALB/c 3T3 fibroblasts during both interphase and mitosis. This centrosomal localization was not disrupted by nocodazole-induced depolymerization of the microtubule cytoskeleton, suggesting that mCCCAP is an integral component of the centrosome rather than simply a microtubule-associated protein. We also cloned human CCCAP (hCCCAP). The 2139 bp open reading frame of hCCCAP encodes an 82.5 kDa protein that is 71% identical to mCCCAP at the amino acid level and has the same predicted secondary structure. Ectopically expressed full-length hCCCAP in human U2-osteosarcoma cells also displayed centrosomal localization during interphase and mitosis. This pattern of localization was abolished by truncations of the N- and C-terminus of the protein. We further discovered that the C-terminal portion of hCCCAP is identical to the human colon cancer autoantigen NY-CO-8 (Human Gene Nomenclature symbol SDCCAG8).