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Purpose: Neuroblastoma is an aggressive childhood disease of the sympathetic nervous system.Treatments are often ineffective and have serious side effects. Because resveratrol, a natural plant product, has been reported to have limited toxicity at chemotherapeutic levels, we investigated its efficacy in the treatment of neuroblastoma as well as its underlying mechanism of action.Experimental Design: Resveratrol was tested in mouse xenograft models of human neuroblastoma and in vitro using human cell lines. Results: Resveratrol inhibited the outgrowth of tumors by as much as 80%.The bioavailability of the drug in serum was in the low micromolar range (2-10 Amol/L) and no accumulation was observed in tumor tissue. When resveratrol levels were increased by peritumor injection, rapid tumor regression occurred. Resveratrol decreased tumor cell viability in vitro by 75% to 90%, resulting from an inhibition of cell proliferation and an induction of apoptosis. Loss of mitochondrial membrane potential was an early response to resveratrol. In addition, resveratrol treatment of isolated mitochondria also led to depolarization, suggesting that the drug may target mitochondria directly. Following depolarization, resveratrol caused the release of cytochrome c and Smac/ Diablo from the mitochondria and subsequently the activation of caspase-9 (4-to 8-fold) and caspase-3 (4-to 6-fold). Conclusions: These studies indicate that, despite low bioavailability, resveratrol is effective at inhibiting tumor growth. Elevated levels of resveratrol enhance its antitumor potency leading to tumor regression, associated with widespread tumor cell death, the underlying mechanism of which involves the direct activation of the mitochondrial intrinsic apoptotic pathway.

Resveratrol (RES), a natural plant polyphenol, has gained interest as a nontoxic chemopreventive agent capable of inducing tumor cell death in a variety of cancer types. However, the early molecular mechanisms of RES-induced apoptosis are not well defined. Using the human breast cancer cell lines MDA-MB-231 and MCF-7, we demonstrate that RES is antiproliferative and induces apoptosis in a concentration-and time-dependent manner. Preceding apoptosis, RES instigates a rapid dissipation of mitochondrial membrane potential by directly targeting mitochondria. This is followed by release of cytochrome c and second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI (Smac/DIABLO) into the cytoplasm and substantial increase in the activities of caspases-9 and -3 in MDA-MB-231 cells. In addition, live cell microscopy demonstrates that RES causes an early biphasic increase in the concentration of free intracellular calcium ([Ca 2ϩ ] i ), probably resulting from depletion of the endoplasmic reticulum stores in breast cancer cells. In caspase-3-deficient MCF-7 cells, apoptosis is mediated by the Ca 2ϩ -activated protease, calpain, leading to the degradation of plasma membrane Ca 2ϩ -ATPase isoform 1 and fodrin; the degradation is attenuated by buffering [Ca 2ϩ ] i and blocked by calpain inhibitors. Mitochondrial permeability transition pore antagonists also blocked calpain activation. In vivo mouse xenograft studies demonstrate that RES treatment inhibits breast cancer growth with no systemic toxicities. Together, these results suggest a critical role for mitochondria not only in the intrinsic apoptotic pathway but also in the Ca 2ϩ and calpain-dependent cell death initiated by RES. Thus, RES may prove useful as a nontoxic alternative for breast cancer treatment.

Guanylyl cyclase activating protein (GCAP1) has been proposed to act as a calcium-dependent regulator of retinal photoreceptor guanylyl cyclase (GC) activity. Using immunocytochemical and biochemical methods, we show here that GCAP1 is present in rod and cone photoreceptor outer segments where phototransduction occurs. Recombinant and native GCAP1 activate recombinant human retGC (outer segment-specific GC) and endogenous GC(s) in rod outer segment (ROS) membranes at low calcium. In addition, we isolate and clone a retinal homolog, termed GCAP2, that shows ~50% identity with GCAP1. Like GCAP1, GCAP2 activates photoreceptor GC in a calcium-dependent manner. Both GCAP1 and GCAP2 presumably act on GCs by a similar mechanism; however, GCAP1 specifically localizes to photoreceptor outer segments, while in these experiments GCAP2 was isolated from extracts of retina but not ROS. These results demonstrate that GCAP1 is an activator of ROS GC, while the finding of a second activator, GCAP2, suggests that a similar mechanism of GC regulation may be present in outer segments, other subcellular compartments of the photoreceptor, or other cell types.In vertebrate photoreceptor cells, the synthesis and hydrolysis of cyclic GMP (cGMP) are critical steps in phototransduction. In response to light, a cascade of reactions in the photoreceptor outer segment leads to the hydrolysis of cGMP and the closure of cGMP-gated cation channels in the outer segment plasma membrane. As a consequence, there is a reduction in the amount of calcium entering the cell. Calcium efflux owing to the Na + :K + , Ca 2+

The complex sensation of vision begins with the relatively simple photoisomerization of the visual pigment chromophore 11‐cis‐retinal to its all‐trans configuration. This event initiates a series of biochemical reactions that are collectively referred to as phototransduction, which ultimately lead to a change in the electrochemical signaling of the photoreceptor cell. To operate in a wide range of light intensities, however, the phototransduction pathway must allow for adjustments to background light. These take place through physiological adaptation processes that rely primarily on Ca2+ ions. While Ca2+ may modulate some activities directly, it is more often the case that Ca2+‐binding proteins mediate between transient changes in the concentration of Ca2+ and the adaptation processes that are associated with phototransduction. Recently, combined genetic, physiological, and biochemical analyses have yielded new insights about the properties and functions of many phototransduction‐specific components, including some novel Ca2+‐binding proteins. Understanding these Ca2+‐binding proteins will provide a more complete picture of visual transduction, including the mechanisms associated with adaptation, and of related degenerative diseases. BioEssays 22:337–350, 2000. © 2000 John Wiley & Sons, Inc.

Recoverin is a member ofthe EF-hand family of calcium-binding proteins involved in the transduction of light by vertebrate photoreceptors. Recoverin also was identified as an autoantigen in the degenerative disease of the retina known as cancer-associated retinopathy (CAR), a paraneoplastic syndrome whereby immunological events lead to the degeneration of photoreceptors in some individuals with cancer. In this study, we demonstrate that recoverin is expressed in the lung tumor of a CAR patient but not in similar tumors obtained from individuals without the associated retinopathy. Recoverin was identified initially by Western blot analysis of the CAR patient's biopsy tissue by using antirecoverin antibodies generated against different regions of the recoverin molecule. In addition, cultured cells from the biopsy tissue expressed recoverin, as demonstrated by reverse transcription-PCR using RNA extracted from the cells. The immunodominant region of recoverin also was determined in this study by a solid-phase immunoassay employing overlapping heptapeptides encompassing the entire recoverin sequence. Two linear stretches of amino acids (residues 64-70, Lys-Ala-Tyr-Ala-Gln-His-Val; and 48-52, Gln-Phe-Gln-SerIle) made up the major determinants. One of the same regions of the recoverin molecule (residues 64-70) also was uniquely immunopathogenic, causing photoreceptor degeneration upon immunization of Lewis rats with the corresponding peptide. These data demonstrate that the neural antigen recoverin more than likely is responsible for the immunological events associated with vision loss in some patients with cancer. These data also establish CAR as one of the few autoimmunemediated diseases for which the specific self-antigen is known.Neurological disorders can be associated with cancer even though the tumor and its metastases have not entered the nervous system (1). These "remote effects" of cancer, or paraneoplastic syndromes, are thought to be autoimmune mediated. The expression of a tumor antigen supposedly leads to an immunological response which then recognizes the same antigen or a shared epitope in the nervous system. The autoimmune basis for a paraneoplastic disease was first demonstrated for Lambert-Eaton myasthenic syndrome, a disorder of the peripheral nervous system in which autoantibodies bind to presynaptic calcium channels at the neuromuscular junction (2, 3), thus interfering with the release of acetylcholine and resulting in proximal muscle weakness and related symptoms. In paraneoplastic cerebellar degeneration, a disease of the central nervous system, autoantibodies to Purkinje cell antigens were detected in patients presenting with ataxia, nystagmus, and dysarthria (4). Upon autopsy, the afflicted individuals displayed widespread loss of Purkinje cells in the cerebellum. A Purkinje cell antigen subsequently was detected in the gynecological tumors associated with these patients but not in similar tumors obtained from individuals without neurological symptoms (5). Paraneoplastic syndromes of...

Abstract. Cancer-associated retinopathy (CAR), a paraneoplastic syndrome, is characterized by the degeneration of retinal photoreceptors under conditions where the tumor and its metastases have not invaded the eye. The retinopathy often is apparent before the diagnosis of cancer and may be associated with autoantibodies that react with specific sites in the retina. We have examined the sera from patients with CAR to further characterize the retinal antigen. Western blot analysis of human retinal proteins reveals a prominent band at 26 kD that is labeled by the CAR antisera. Antibodies to the 26-kD protein were affinity-purified from complex CAR antisera and used for EMimmunocytochemical localization of the protein to the nuclei, inner and outer segments of both rod and cone cells. Other antibodies obtained from the CAR sera did not label photoreceptors. Using the affinitypurified antibodies for detection, the 26-kD protein, designated p26, was purified to homogeneity from the outer segments of bovine rod photoreceptor cells by Phenyl-Sepharose and ion exchange chromatography. Partial amino acid sequence of p26 was determined by gas phase Edman degradation and revealed extensive homology with a cone-specific protein, visinin. Based upon structural relatedness, both the p26 rod protein and visinin are members of the calmodulin family and contain calcium binding domains of the E-F hand structure.variety of neurodegenerative diseases are known to be associated with different types of cancer, even though the tumor and its metastases have not invaded the nervous system (Brain and Norris, 1965;Brain and Wilkinson, 1965;

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