The baculovirus anti-apoptotic p35 protein promotes transformation of mouse embryo fibroblasts

Cisplatin induces mitochondrial deficits in Drosophila larval segmental nerve

Cisplatin is an effective chemotherapy drug that induces peripheral neuropathy in cancer patients. In rodent dorsal root ganglion neurons, cisplatin binds nuclear and mitochondrial DNA (mtDNA) inducing DNA damage and apoptosis. Platinum-mtDNA adducts inhibit mtDNA replication and transcription leading to mitochondrial degradation. Cisplatin also induces climbing deficiencies associated with neuronal apoptosis in adult Drosophila melanogaster. Here we used Drosophila larvae that express green fluorescent protein in the mitochondria of motor neurons to observe the effects of cisplatin on mitochondrial dynamics and function. Larvae treated with 10μg/ml cisplatin had normal survival with deficiencies in righting and heat sensing behavior. Behavior was abrogated by, the pan caspase inhibitor, p35. However, active caspase 3 was not detected by immunostaining. There was a 27% decrease in mitochondrial membrane potential and a 42% increase in reactive oxygen species (ROS) in mitochondria along the axon. Examination of mitochondrial axonal trafficking showed no changes in velocity, flux or mitochondrial length. However, cisplatin treatment resulted in a greater number of stationary organelles caused by extended pausing during axonal motility. These results demonstrate that cisplatin induces behavior deficiencies in Drosophila larvae, decreased mitochondrial activity, increased ROS production and mitochondrial pausing without killing the larvae. Thus, we identified particular aspects of mitochondrial dynamics and function that are affected in cisplatin-induced peripheral neuropathy and may represent key therapeutic targets.

Evolution and function of the p35 family of apoptosis inhibitors

Apoptosis is a common cellular response to virus infection. However, many viruses have evolved strategies, such as the expression of anti-apoptotic proteins, to combat this response. One such family of anti-apoptotic viral proteins is the p35 family of caspase inhibitors, which are expressed by certain insect viruses. Expression of p35 prevents the host cell from undergoing apoptosis, thereby allowing for propagation of the virus. p35 family members are potent inhibitors of caspases. Members of the family fall into one of three groups that inhibit different classes of caspases. Since the discovery of the first p35 gene in 1991, the anti-apoptotic function of this protein family has been studied extensively. This unique type of protease inhibitor has proven to be extremely useful in the study of apoptosis in experimental settings ranging from nematodes to mammals.

Baculovirus p35 increases pancreatic β-cell resistance to apoptosis

beta-cells die by apoptosis in type 1 diabetes as a result of autoimmune attack mediated by cytokines, and in type 2 diabetes by various perpetrators including human islet amyloid polypeptide (hIAPP). The cascade of apoptotic events induced by cytokines and hIAPP is mediated through caspases and reactive oxygen species. The baculovirus p35 protein is a potent anti-apoptotic agent shown to be effective in a variety of species and able to inhibit a number of apoptotic pathways. Here, we aimed at determining the protective potential of p35 in beta-cells exposed to cytokines and hIAPP, as well as the effects of p35 on beta-cell function. The p35 gene was introduced into betaTC-tet cells, a differentiated murine beta-cell line capable of undergoing inducible growth-arrest. Both proliferating and growth-arrested cells expressing p35 manifested increased resistance to cytokines and hIAPP, compared with control cells, as judged by cell viability, DNA fragmentation, and caspase-3 activity assays. p35 was significantly more protective in growth-arrested, compared with proliferating, cells. No significant differences were observed in proliferation and insulin content between cells expressing p35 and control cells. In contrast, p35 manifested a perturbing effect on glucose-induced insulin secretion. These findings suggest that p35 could be incorporated as part of a multi-pronged approach of immunoprotective strategies to provide protection from recurring autoimmunity for transplanted beta-cells, as well as in preventive gene therapy in type 1 diabetes. p35 may also be protective from beta-cell damage caused by hIAPP in type 2 diabetes.

Baculovirus P35 interacts with a subunit of human RNA polymerase II and can enhance promoter activity in human cells

The early protein P35 from the baculovirus Autographa californica nucleopolyhedrovirus is a direct inhibitor of caspases and can block apoptosis in a wide variety of systems. In addition, it has been linked to the regulation of viral gene expression, shut-down of protein synthesis in infected insect cells and malignant transformation of mouse fibroblasts. By yeast-two-hybrid screening we identified the RPB11a subunit of human RNA polymerase II as an interaction partner of P35. Specificity of the interaction was confirmed by affinity blotting. By immunocytology, P35 was in part found in the nucleus of transfected cells. Homology searches further revealed that P35 has structural similarity with RPB3, the subunit of RNA polymerase II that has been demonstrated to interact directly with RPB11a. When transfected into human colon carcinoma cells, P35 was able to enhance the activity of E-cadherin and beta-actin promoters by about a factor of two as measured by luciferase reporter assay. P35 and hRPB11a together enhanced the E-cadherin activity about three- to fourfold. These data suggest an additional role for P35 in the regulation of cellular transcription.

Baculoviruses as Vectors for Gene Therapy against Human Prostate Cancer

Current curative strategies for prostate cancer are restricted to the primary tumour, and the effect of treatments to control metastatic disease is not sustained. Therefore, the application of gene therapy to prostate cancer is an attractive alternative. Baculoviruses are highly restricted insect viruses, which can enter, but not replicate in mammalian cells. Baculoviruses can incorporate large amounts of extra genetic material, and will express transgenes in mammalian cells when under the control of a mammalian or strong viral promoter. Successful gene delivery has been achieved both in vitro and in vivo and into both dividing and nondividing cells, which is important since prostate cancers divide relatively slowly. In addition, the envelope protein gp64 is sufficiently mutable to allow targeted transduction of particular cell types. In this review, the advantages of using baculoviruses for prostate cancer gene therapy are explored, and the mechanisms of viral entry and transgene expression are described.

Apoptosis regulators and their role in tumorigenesis

It has become clear that, together with deregulated growth, inhibition of programmed cell death (PCD) plays a pivotal role in tumorigenesis. In this review, we present an overview of the genes and mechanisms involved in PCD. We then summarize the evidence that impaired PCD is a prerequisite for tumorigenesis, as indicated by the fact that more and more neoplastic mutations appear to act by interfering with PCD. This has made the idea of restoration of corrupted 'death programs' an intriguing new area for potential cancer therapy.

Reversible resistance to apoptosis in cutaneous T cell lymphoma

Mycosis fungoides and its leukemic variant, Sézary syndrome, represent the most common forms of cutaneous T cell lymphomas (CTCL). These disorders are clonal neoplasms characterized by the progressive accumulation of cells that resemble activated/memory CD4+ T cells. Unlike their normal counterparts, these malignant lymphocytes have prolonged life spans and are resistant to dying following treatment with most chemotherapeutic agents. This suggests that CTCL undergo abnormal programmed cell death; however, data regarding apoptotic defects in CTCL are limited. Regulation of apoptosis in lymphocytes that regularly undergo clonal expansion is necessarily complex and will be reviewed here. Clonally expanded lymphocytes rely primarily on Fas-mediated pathways to initiate apoptosis. Factors leading to the resistance of apoptosis in CTCL and new therapeutic approaches for reversing this resistance will be discussed, including the important role that the Fas death pathway may play in the pathogenesis and treatment of CTCL.

Viruses and apoptosis

Successful viral replication requires not only the efficient production and spread of progeny, but also evasion of host defense mechanisms that limit replication by killing infected cells. In addition to inducing immune and inflammatory responses, infection by most viruses triggers apoptosis or programmed cell death of the infected cell. This cell response often results as a compulsory or unavoidable by-product of the action of critical viral replicative functions. In addition, some viruses seem to use apoptosis as a mechanism of cell killing and virus spread. In both cases, successful replication relies on the ability of certain viral products to block or delay apoptosis until sufficient progeny have been produced. Such proteins target a variety of strategic points in the apoptotic pathway. In this review we summarize the great amount of recent information on viruses and apoptosis and offer insights into how this knowledge may be used for future research and novel therapies.

Synthetic peptide sequence from the C-terminus of the insulin-like growth factor-I receptor that induces apoptosis and inhibition of tumor growth

Although the type 1 insulin-like growth factor receptor (IGF-IR) is a potent inhibitor of apoptosis, its C-terminus sequence sends contradictory signals, including a clearly proapoptotic signal. We have synthesized a peptide, peptide 2, having the sequence of the IGF-IR from residue 1282 to residue 1298 (C-terminus of the beta subunit). To favor its uptake into cells, we linked it to a stearic acid moiety at its NH-terminus. Peptide 2 is taken up by the cells, where it inhibits DNA synthesis and causes apoptosis, while a scrambled peptide (with stearic acid) and peptide 2 without stearic acid are completely ineffective. Peptide 2 is more effective when cells are in anchorage-independent conditions than when they grow in monolayer cultures. Accordingly, we find that peptide 2 can inhibit the growth of a human prostatic cell line in nude mice. The proapoptotic effect of peptide 2 is inhibited by the expression of Bcl-2 or by a dominant negative mutant of caspase 9. These and other data indicate that peptide 2 does not seem to be competing directly with the IGF-IR for common substrates, but that its proapoptotic effect is related to its ability to activate the caspase cascade.