Ann M. Bode

Post-translational modification of p53 in tumorigenesis

Interest in the tumour suppressor p53 has generated much information regarding the complexity of its function and regulation in carcinogenesis. However, gaps still exist in our knowledge regarding the role of p53 post-translational modifications in carcinogenesis and cancer prevention. A thorough understanding of p53 will be extremely useful in the development of new strategies for treating and preventing cancer, including restoration of p53 function and selective killing of tumours with mutant TP53.

Biology of free radical scavengers: an evaluation of ascorbate.

Reactive free radical species (R∗) are associated with several forms of tissue damage and disease, and also with the process of aging. Protection is thought to be available in the form of endogenous compounds that react with and thereby “scavenge” the R∗. Because many R∗ are reactive forms of oxygen, an effective scavenger is often referred to as an antioxidant. To be an effective antioxidant physiologically, a substance must have certain chemical and biological properties: it must be present in adequate amounts in the body; it must react with a variety of R∗; it must be suitable for compartmentation; it must be readily available; it might be suitable for regeneration; it must be conserved by the kidneys; and it must have tolerable toxicity. Several water‐soluble candidates are mentioned, with most having no more than one or two of the attributes listed. Ascorbic acid is discussed in detail, and an analysis is made of whether it has the properties mentioned.—Rose, R. C., Bode, A. M. Biology of free radical scavengers: an evaluation of ascorbate. FASEB J. 7: 1135‐1142; 1993.

Molecular targets of phytochemicals for cancer prevention

Although successful for a limited number of tumour types, the efficacy of cancer therapies, especially for late-stage disease, remains poor overall. Many have argued that this could be avoided by focusing on cancer prevention, which has now entered the arena of targeted therapies. During the process of identifying preventive agents, dietary phytochemicals, which are thought to be safe for human use, have emerged as modulators of key cellular signalling pathways. The task now is to understand how these chemicals perturb these pathways by modelling their interactions with their target proteins.

Mitogen-Activated Protein Kinase Activation in UV-Induced Signal Transduction

Experimental evidence supported by epidemiological findings suggests that solar ultraviolet (UV) irradiation is the most important environmental carcinogen leading to the development of skin cancers. Because the ozone layer blocks UVC (wavelength, 180 to 280 nm) exposure, UVA (UVA I, 340 to 400 nm; UVA II, 320 to 340 nm) and UVB (280 to 320 nm) are probably the chief carcinogenic components of sunlight with relevance for human skin cancer. Substantial contributions to the elucidation of the specific signal transduction pathways involved in UV-induced skin carcinogenesis have been made over the past few years, and most evidence suggests that the cellular signaling response is UV wavelength-dependent. The mitogen-activated protein kinase (MAPK) signaling cascades are targets for UV and are important in the regulation of the multitude of UV-induced cellular responses. Experimental studies have used a range of UVA, UVB, UVC, and various combinations in multiple doses, and the observed effects on activation and phosphorylation of MAPKs are varied. This review focuses on the mechanistic data supporting a role for MAPKs in UV-induced skin carcinogenesis. Progress in understanding the mechanisms of UV-induced signal transduction could lead to the use of these protein kinases as specific targets for the prevention and control of skin cancer. Sunlight is most likely the main cause of skin cancer, which is the most common human cancer. Solar radiation is categorized by wavelength into ultraviolet C (UVC, wavelength 180 to 280 nm), ultraviolet B (UVB, 280 to 320 nm), and ultraviolet A (UVA) regions (UVA I, 340 to 400 nm; UVA II, 320 to 340 nm). All UV spectra have been linked to cancer in experimental animal models. However, the physiologic relevance of UVC may be dubious because all of the UVC radiation is absorbed by the ozone layer of Earths atmosphere. UV radiation at Earths surface consists of 1 to 10% UVB and 90 to 99% UVA and can penetrate human skin, making it the primary target for UV-induced damage and cancer. UV exposure can result in direct or indirect DNA damage, depending on the wavelength and exposure time. Even though DNA damage is a primary initiator in UV-induced skin carcinogenesis, the mechanism behind the tumor-promoting ability of UV is unclear. The assumption in the past was that the mechanisms of UV-stimulated tumor promotion could be based on studies of UVC-induced signal transduction, because the effects were assumed to be similar for all wavelengths of UV. However, accumulating evidence suggests that the cellular responses produced by UV irradiation are likely to be wavelength-dependent. UV activates various signaling pathways that are either oncogenic or protective or both. Many of these pathways are mediated primarily through signaling cascades involving mitogen-activated protein kinases (MAPKs), resulting in the modification of transcription factors such as activator protein-1, which can lead to skin cancer. In light of rising public concern over the increased incidence of skin cancer, this review focuses on the mechanistic data supporting a role for MAPKs in UV-stimulated skin carcinogenesis. Progress in understanding the mechanisms of UV-induced signal transduction could lead to the use of these protein kinases as specific targets for the prevention and control of skin cancer.

The paradox of arsenic: molecular mechanisms of cell transformation and chemotherapeutic effects

Arsenic is a well-documented carcinogen that also appears to be a valuable therapeutic tool in cancer treatment. This creates a paradox for which no unified hypothesis has been reached regarding the molecular mechanisms that determine whether arsenic will act as a carcinogen or as an effectual chemotherapeutic agent. Much of our knowledge with respect to the actions of arsenic has been drawn from epidemiological or clinical studies. The actions of arsenic are likely to be related to cell type, arsenic species, and length and dose of exposure. Arsenic unquestionably induces apoptosis and may specifically target certain tumor cells. Research data strongly suggest that arsenic influences distinct signaling pathways involved in mediating proliferation or apoptosis, including mitogen-activated protein kinases, p53, activator protein-1 or nuclear factor kappa B. The primary purpose of this review is to examine recent findings, from this laboratory and others, that focus on the molecular mechanisms of arsenics actions in cell transformation and as a therapeutic agent.

(−)−Epigallocatechin Gallate Overcomes Resistance to Etoposide-Induced Cell Death by Targeting the Molecular Chaperone Glucose-Regulated Protein 78

Many beneficial properties have been attributed to (-)-epigallocatechin gallate (EGCG), including chemopreventive, anticarcinogenic, and antioxidant actions. In this study, we investigated the effects of EGCG on the function of glucose-regulated protein 78 (GRP78), which is associated with the multidrug resistance phenotype of many types of cancer cells. Our investigation was directed at elucidating the mechanism of the EGCG and GRP78 interaction and providing evidence about whether EGCG modulates the activity of anticancer drugs through the inhibition of GRP78 function. We found that EGCG directly interacted with GRP78 at the ATP-binding site of protein and regulated its function by competing with ATP binding, resulting in the inhibition of ATPase activity. EGCG binding caused the conversion of GRP78 from its active monomer to the inactive dimer and oligomer forms. Further, we showed that EGCG interfered with the formation of the antiapoptotic GRP78-caspase-7 complex, which resulted in an increased etoposide-induced apoptosis in cancer cells. We also showed that EGCG significantly suppressed the transformed phenotype of breast cancer cells treated with etoposide. Overall, these results strongly suggested that EGCG could prevent the antiapoptotic effect of GRP78, which usually suppresses the caspase-mediated cell death pathways in drug-treated cancer cells, contributing to the development of drug resistance.

The functional contrariety of JNK.

The JNK proteins are activated by multiple and diverse stimuli, leading to varied and seemingly contradictory cellular responses. In particular, JNKs have been reported to have a role in the induction of apoptosis, but have also been implicated in enhancing cell survival and proliferation. Thus the JNK proteins seem to represent an archetype of contrariety of intracellular signaling. The opposing roles of JNKs have been attributed to the observation that JNKs activate different substrates based on specific stimulus, cell type or temporal aspects. Because of their analogous expression in apparently almost every tissue, JNK1 and JNK2 have most often been considered to have overlapping or redundant functions. In spite of this assessment, research evidence suggests that the functions of JNKs should be addressed in a manner that differentiates between their precise contributions. Specifically in this review, we examine evidence regarding whether the JNKs proteins might play distinctive roles in cellular processes associated with carcinogenesis.

OCULAR OXIDANTS AND ANTIOXIDANT PROTECTION

Abstract Oxidative damage and antioxidant protection in ocular tissues has not been reviewed recently. Metabolism in the eye is of increasing interest because the organ is highly susceptible to damage by sunlight, oxygen, various chemicals, and pollutants. Interest is expected to increase because of an aging Western world population and a continued depletion of stratospheric ozone. Hydrogen peroxide is discussed because it is both a byproduct and a source of free radical reactions and is normally present in the aqueous humor. The metabolism of reactive oxygen species by enzymes, nutrients, pigments, and low molecular weight scavengers is evaluated. Ascorbic acid, because of its high concentration in the eye, is thought to be a primary substrate in ocular protection; progress in determining the mechanisms by which it is recycled and maintained in the useful, reduced state is discussed. Recent information is included about antioxidants not previously known to be present in the eye, and some importance is placed on the properties of the vitreous humor and tear fluid because of the previous lack of emphasis on these.

Raf and MEK Protein Kinases Are Direct Molecular Targets for the Chemopreventive Effect of Quercetin, a Major Flavonol in Red Wine

Considerable attention has focused on the health-promoting effects of red wine and its nonflavonoid polyphenol compound resveratrol. However, the underlying molecular mechanisms and molecular target(s) of red wine or other potentially active ingredients in red wine remain unknown. Here, we report that red wine extract (RWE) or the red wine flavonoid quercetin inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced transformation of JB6 promotion-sensitive mouse skin epidermal (JB6 P+) cells. The activation of activator protein-1 and nuclear factor-kappaB induced by TPA was dose dependently inhibited by RWE or quercetin treatment. Western blot and kinase assay data revealed that RWE or quercetin inhibited mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK) 1 and Raf1 kinase activities and subsequently attenuated TPA-induced phosphorylation of ERK/p90 ribosomal S6 kinase. Although either RWE or quercetin suppressed Raf1 kinase activity, they were more effective in inhibiting MEK1 activity. Importantly, quercetin exerted stronger inhibitory effects than PD098059, a well-known pharmacologic inhibitor of MEK. Resveratrol did not affect either MEK1 or Raf1 kinase activity. Pull-down assays revealed that RWE or quercetin (but not resveratrol) bound with either MEK1 or Raf1. RWE or quercetin also dose dependently suppressed JB6 P+ cell transformation induced by epidermal growth factor or H-Ras, both of which are involved in the activation of MEK/ERK signaling. Docking data suggested that quercetin, but not resveratrol, formed a hydrogen bond with the backbone amide group of Ser(212), which is the key interaction for stabilizing the inactive conformation of the activation loop of MEK1.

Involvement of the Acid Sphingomyelinase Pathway in UVA-induced Apoptosis

The sphingomyelin-ceramide pathway is an evolutionarily conserved ubiquitous signal transduction system that regulates many cell functions including apoptosis. Sphingomyelin (SM) is hydrolyzed to ceramide by different sphingomyelinases. Ceramide serves as a second messenger in mediating cellular effects of cytokines and stress. In this study, we find that acid sphingomyelinase (SMase) activity was induced by UVA in normal JY lymphoblasts but was not detectable in MS1418 lymphoblasts from Niemann-Pick type D patients who have an inherited deficiency of acid SMase. We also provide evidence that UVA can induce apoptosis by activating acid SMase in normal JY cells. In contrast, UVA-induced apoptosis was inhibited in MS1418 cells. Exogenous SMase and its product, ceramide (10–40 μm), induced apoptosis in JY and MS1418 cells, but the substrate of SMase, SM (20–80 μm), induced apoptosis only in JY cells. These results suggest that UVA-induced apoptosis by SM is dependent on acid SMase activity. We also provide evidence that induction of apoptosis by UVA may occur through activation of JNKs via the acid SMase pathway.