Reactive oxygen species‐dependent destruction of MEK and Akt in Manumycin stimulated death of lymphoid tumor and myeloma cell lines

Abstract

Manumycin-A (Man-A) is a farnesyltransferase inhibitor (FTI), which was originally identified as an effective tumoricide against several cancers, especially ones harboring constitutively active Ras. However, it is becoming apparent that Man-A can stimulate tumor death independently of FTases. Antioxidant treatment blocked Man-A-stimulated DNA damage and reversed Man-Ainhibited tumor growth. However, the precise molecular details of how these reactive oxygen species (ROS) influence cell signaling modules are poorly understood. We examined how ROS may modulate death and survival pathways in a panel of tumor cells. Man-A treatment resulted in a massive induction of superoxide anion (AEO 2 2 ) only in Man-A-sensitive tumors. Within 1 hr, Man-A caused the ROS-dependent activation of caspases 9 and 3. In this time-frame, the Ras-Raf target, MEK, and the survival protein Akt were dephosphorylated in ROS-dependent fashions and then cleaved in ROS and caspase-dependent manners. Pretreatment with ROS scavengers blocked the adverse effects of Man-A, including the processing of caspases and the cleavage of MEK and Akt. These events were noted before any losses in Ras activity or changes in its maturation could be detected. Finally, transfection with cDNAs encoding the antioxidant enzymes catalase, superoxide dismutase and thioredoxin reductase inhibited superoxide induction and apoptosis. Together, our data suggest that the elimination of tumors by Man-A can be independent of the inhibiting of Ras. However, one universal feature observed is the generation of death-triggering intracellular oxidants that appear to directly participate in the select targeting of growth and survival proteins that then either augment or ensure tumor cell death. ' 2007 Wiley-Liss, Inc.Key words: Manumycin; farnesyltransferase inhibitor; MEK; Akt; reactive oxygen species; cleavage; caspase; Ras Ras is a small, 21 kDa, guanosine triphosphate (GTP)-binding protein, which controls numerous cellular functions including growth and proliferation as well as providing scaffolding for other signaling enzymes. Ras regulates the PI3K/Akt and PI3K/mTOR/ p70 S6K signaling modules, which drive cell proliferation, cell growth and survival. 1 Furthermore, the canonical Ras signaling network (Ras/Raf/MEK/ERK) regulates anabolism, induces growth-enhancing genes through transcription factors such as Elk-1 and it also suppresses the activities of proapoptotic proteins. 2 Hence, it is not surprising that 30% of known human tumors and 90% of pancreatic carcinomas, one of the most aggressive and morbid types of cancer, harbor mutated or dysfunctional Ras. [3][4][5] Together these features make Ras an attractive target for cancer therapy.Ras maturation requires the post-translational transfer of a farnesyl hydrocarbon group to its C-terminal cysteine in a process termed prenylation, 6-8 which is essential for the subsequent localization of Ras at the plasma membrane where receptor signals regulate its on and off state. 9 Because prenylation is also required for subsequen...

Manumycin A induces apoptosis in malignant pleural mesothelioma through regulation of Sp1 and activation of the mitochondria-related apoptotic pathway

“…Recently, the anti-neoplastic activity of Manu A has been demonstrated in various experimental systems (18). It exerts antitumor activity against a variety of cancer cells such as human pancreatic cancer cells (19), anaplastic thyroid cancer cells (20,21), human colon tumor cells (22) and human hepatocellular carcinoma HepG2 cells (23), medulloblastoma cells (24,25), leukemic cells (26), lymphoid tumor and myeloma cell lines (27,28). However, little is known concerning the anticancer mechanisms of Manu A by which it can induce apoptosis in MPM cells.…”

Antitumor activity of asukamycin, a secondary metabolite from the actinomycete bacterium Streptomyces nodosus subspecies asukaensis

“…Even though inhibition of farnesyltransferase may account for the antiproliferative effects of manumycins, recent data indicate that manumycins induce tumor cell death independently of farnesyltransferase and inhibition of ras signal transduction pathways (21). Manumycin-induced apoptosis in tumor cells has been shown by measuring various parameters including release of mitochondrial cytochrome c into the cytosol, activation of caspases 8, 9 and 3, as well as increased DNA fragmentation (6,7,9,21,22).…”

“…Manumycin-induced apoptosis in tumor cells has been shown by measuring various parameters including release of mitochondrial cytochrome c into the cytosol, activation of caspases 8, 9 and 3, as well as increased DNA fragmentation (6,7,9,21,22). She et al (7) suggested that the cellular death induced by manumycin in human thyroid cancer cells fits the general pattern of xenobiotic-induced apoptosis, which is characterized by induction of oxidative stress, MAPK signaling (p38 MAPK in particular), release of cytochrome c and subsequent activation of the apoptotic pathways (reviewed in ref.…”

Enhancing Therapeutic Radiation Responses in Multiple Myeloma

“…(Karp and Lancet, 2005;Santucci et al, 2003). Manumycin (Man)-A induces apoptosis in B-c e l l t u m o r s b y i n h i biting prenylation (Frassanito et al, 2002) and also by generating ROS that inhibits Ras/MEK/ERK and Ras/PI3K/Akt pathways by cleaving MEK and Akt (Sears et al, 2008). R115777 (zarnestra/tipifarnib) is a FTI that has shown promising clinical results in acute myeloid leukemia, myelodysplastic syndromes, chronic myelogenous leukemia, and MM and with anti-tumor effects noted independent of Ras mutations (Martinelli et al, 2008).…”