Dynein light chain binding determines complex formation and posttranslational stability of the Bcl-2 family members Bmf and Bim.

The BH3-only class of Bcl-2 family proteins triggers mitochondrial apoptosis. Several mechanisms are used to restrain the pro-apoptotic activity of these proteins. Dynein light chain (DYNLL) 1 and 2 has been proposed to negatively regulate the activity of Bim and Bmf, respectively, and the Bim-DYNLL1 interaction leads to the formation of large protein complexes on mitochondria. Here we found that Bim and Bmf interact with both isoforms of DYNLL (DYNLL1 and DYNLL2). DYNLL1/2 not only induced homo-dimerization of Bim and Bmf but also led to the formation of ternary complexes (Bim-DYNLL-Bmf), both in cell-free and in cellular systems. DYNLL-induced oligomerization stabilized Bmf in cultured cells and inhibited its degradation by the ubiquitin-independent 20S proteasome in a cell-free system. Surprisingly, overexpression of wild-type Bmf but not of a DYNLL-binding-deficient mutant induced degradation of endogenous Bim in different cell lines, but both variants sensitized to apoptosis. Mutant Bmf incapable of interacting with anti-apoptotic Bcl-2 proteins and of inducing apoptosis still caused Bim degradation. These results suggest that Bmf overexpression-induced Bim degradation is not due to the displacement of Bim from anti-apoptotic Bcl-2 proteins but a direct consequence of the modulation of Bim-DYNLL association. A peptide derived from the DYNLL-binding domain of Bim also led to the degradation of Bim as well as of its preferred binding partner Mcl-1. Thus DYNLL regulates the mitochondrial pathway of apoptosis by determining the stability of Bmf, Bim, and Mcl-1 proteins.

The established and the predicted roles of dynein light chain in the regulation of mitochondrial apoptosis.

The mitochondrial pathway of apoptosis is regulated by the interplay between the members of Bcl-2 family. Within this family, BH3-only proteins are the sensors of apoptotic stimuli and can trigger apoptosis either by inhibiting the anti-apoptotic Bcl-2-family proteins or by directly activating the effectors Bax and Bak. An expanding body of research suggests that a number of non-Bcl-2 proteins can also interact with Bcl-2 proteins and contribute to the decision of cell fate. Dynein light chain (LC8, DYNLL or DLC), a hub protein and a dimerizing engine has been proposed to regulate the pro-apoptotic activity of two BH3-only proteins, Bim and Bmf. Our recent work has provided insight into the mechanisms through which DLC1 (DYNLL1) modulates Bim activity. Here we discuss the present day understanding of Bim-DLC interaction and endeavor to evaluate this interaction in the light of information from studies of DLC with other binding partners.

Dynein light chain 1 induces assembly of large Bim complexes on mitochondria that stabilize Mcl-1 and regulate apoptosis.

The Bcl-2 family protein Bim triggers mitochondrial apoptosis. Bim is expressed in nonapoptotic cells at the mitochondrial outer membrane, where it is activated by largely unknown mechanisms. We found that Bim is regulated by formation of large protein complexes containing dynein light chain 1 (DLC1). Bim rapidly inserted into cardiolipin-containing membranes in vitro and recruited DLC1 to the membrane. Bim binding to DLC1 induced the formation of large Bim complexes on lipid vesicles, on isolated mitochondria, and in intact cells. Native gel electrophoresis and gel filtration showed Bim-containing mitochondrial complexes of several hundred kilodaltons in all cells tested. Bim unable to form complexes was consistently more active than complexed Bim, which correlated with its substantially reduced binding to anti-apoptotic Bcl-2 proteins. At endogenous levels, Bim surprisingly bound only anti-apoptotic Mcl-1 but not Bcl-2 or Bcl-XL, recruiting only Mcl-1 into large complexes. Targeting of DLC1 by RNAi in human cell lines induced disassembly of Bim-Mcl-1 complexes and the proteasomal degradation of Mcl-1 and sensitized the cells to the Bcl-2/Bcl-XL inhibitor ABT-737. Regulation of apoptosis at mitochondria thus extends beyond the interaction of monomers of proapoptotic and anti-apoptotic Bcl-2 family members but involves more complex structures of proteins at the mitochondrial outer membrane, and targeting complexes may be a novel therapeutic strategy.

HN protein of Newcastle disease virus sensitizes HeLa cells to TNF-α-induced apoptosis by downregulating NF-κB expression.

Hemagglutinin neuraminidase (HN) is a membrane protein of Newcastle disease virus (NDV) with the ability to induce apoptosis in many transformed cell lines. TNF-α is a multi-factorial protein that regulates cell survival, differentiation and apoptosis. In a previous study, we reported that HN protein induces apoptosis by downregulating NF-κB expression. Further, we speculated that downregulation of NF-κB expression might sensitize HeLa cells to TNF-α-mediated apoptosis. Therefore, the present study was undertaken to investigate if HN protein could sensitize HeLa cells to TNF-α and to examine the apoptotic potential of the HN protein and TNF-α in combination. The results revealed that the pro-apoptotic effects were more pronounced with the combination of HN and TNF-α than with HN or TNF-α alone, which indicates that the HN protein indeed sensitized the HeLa cells to TNF-α-induced cell death. The results of the study provide a mechanistic insight into the apoptotic action of HN protein along with TNF-α, which could be valuable in treating tumor types that are naturally resistant to TNF-α.

G1-4A, a Polysaccharide from Tinospora cordifolia Inhibits the Survival of Mycobacterium tuberculosis by Modulating Host Immune Responses in TLR4 Dependent Manner.

Rapid emergence of drug resistance in Mycobacterium tuberculosis (MTB) is a major health concern and demands the development of novel adjunct immunotherapeutic agents capable of modulating the host immune responses in order to control the pathogen. In the present study, we sought to investigate the immunomodulatory effects of G1-4A, a polysaccharide derived from the Indian medicinal plant Tinospora cordifolia, in in-vitro and aerosol mouse models of MTB infection. G1-4A treatment of MTB infected RAW264.7 macrophages significantly induced the surface expression of MHC-II and CD-86 molecules, secretion of proinflammatory cytokines (TNF-α, IL-ß, IL-6, IL-12, IFN-γ) and nitric oxide leading to reduced intracellular survival of both drug sensitive (H37Rv) as well as multi drug resistant strains (Beijing and LAM) of MTB, which was partially attributed to G1-4A induced NO production in TLR4-MyD88 dependent manner. Similarly, bacillary burden was significantly reduced in the lungs of MTB infected BALB/c mice treated with G1-4A, with simultaneous up-regulation of the expression of TNF-α, INF-γ and NOS2 in the mouse lung along with increased levels of Th1 cytokines like IFN-γ, IL-12 and decreased levels of Th2 cytokine like IL-4 in the serum. Furthermore, combination of G1-4A with Isoniazid (INH) exhibited better protection against MTB compared to that due to INH or G1-4A alone, suggesting its potential as adjunct therapy. Our results demonstrate that modulation of host immune responses by G1-4A might improve the therapeutic efficacy of existing anti-tubercular drugs and provide an attractive strategy for the development of alternative therapies to control tuberculosis.

The deubiquitinase Usp27x stabilizes the BH3-only protein Bim and enhances apoptosis.

Bim is a pro-apoptotic Bcl-2 family member of the BH3-only protein subgroup. Expression levels of Bim determine apoptosis susceptibility in non-malignant and in tumour cells. Bim protein expression is downregulated by proteasomal degradation following ERK-dependent phosphorylation and ubiquitination. Here, we report the identification of a deubiquitinase, Usp27x, that binds Bim upon its ERK-dependent phosphorylation and can upregulate its expression levels. Overexpression of Usp27x reduces ERK-dependent Bim ubiquitination, stabilizes phosphorylated Bim, and induces apoptosis in PMA-stimulated cells, as well as in tumour cells with a constitutively active Raf/ERK pathway. Loss of endogenous Usp27x enhances the Bim-degrading activity of oncogenic Raf. Overexpression of Usp27x induces low levels of apoptosis in melanoma and non-small cell lung cancer (NSCLC) cells and substantially enhances apoptosis induced in these cells by the inhibition of ERK signalling. Finally, deletion of Usp27x reduces apoptosis in NSCLC cells treated with an EGFR inhibitor. Thus, Usp27x can trigger via its proteolytic activity the deubiquitination of Bim and enhance its levels, counteracting the anti-apoptotic effects of ERK activity, and therefore acts as a tumour suppressor.

HN Protein of Newcastle Disease Virus Induces Apoptosis Through SAPK/JNK Pathway.

Many viral proteins are responsible for causing induction of apoptosis in the target cells. Hemagglutinin neuraminidase (HN), a multifunctional protein of Newcastle disease virus (NDV), is one of such proteins. The present study was undertaken to determine the apoptotic potential of the HN gene in cultured human cervical cancer cell line (HeLa cell) and to elucidate the molecular mechanisms involved. The results of the study indicate that HN protein causes apoptosis in HeLa cells, as observed by the translocation of Phosphatidylserine, activation of caspases, cleavage of poly (ADP-ribose) polymerase (PARP), and DNA fragmentation. Further, we report that expression of HN protein upregulates the SAPK/JNK pathway leading to transactivation of c-Jun which in turn activates apoptosis signaling. The results of our study provide an insight into the mechanism through which HN induces apoptosis.

Administration of IκB-kinase inhibitor PS1145 enhances apoptosis in DMBA-induced tumor in male Wistar rats.

Nuclear factor kappa-B (NF-κB), a key anti-apoptotic factor, plays a critical role in tumor cell growth, metastasis, and angiogenesis. The transcriptional activity of NF-κB is normally suppressed in the cytoplasm due to its association with a natural inhibitor molecule IκB. Phosphorylation of the IκB at Ser 32 and Ser 36 by the IκB kinase complex (IKK) marks the degradation of the molecule by 26S proteasome. As NF-κB is constitutively activated in most of the tumor cells, inhibition of the activities of IKK may significantly sensitize the tumor cells to apoptosis. In the present study, we investigated the effect of IκB kinase-specific blocker PS1145 on DMBA-induced skin tumor of male Wistar rats. We examined the apoptotic effect of PS1145 on DMBA-induced tumor by various histopathological and molecular techniques. Our results demonstrate the significant expression of major pro-apoptotic genes like caspases 2, 3, 8, 9, and p53 in PS1145-treated tumor bearing group at mRNA levels as well as significant (P < 0.05) down regulation in the expression levels of NF-κB and VEGF, the major pro-inflammatory and pro-angiogenic factors, respectively. The histopathological examination showed that the tumor progression, mitotic, AgNOR, and PCNA indices were significantly reduced in PS1145 treatment groups as compared to PBS control on day 28 of post-treatment. Furthermore, significant increase in TUNEL positive nuclei and observation of peculiar apoptotic nuclei in transmission electron microscopy were seen in PS1145 treatment group. We conclude that intravenous application of PS1145 promotes direct apoptosis in DMBA-induced skin tumor in male Wistar rats by blocking NF-κB and VEGF activities.

Regulation of Liver Enriched Transcription Factors in Rat Hepatocytes Cultures on Collagen and EHS Sarcoma Matrices.

Liver-enriched transcription factors (LETF) play a crucial role in the control of liver-specific gene expression and for hepatocytes to retain their molecular and cellular functions complex interactions with extra cellular matrix (ECM) are required However, during cell isolation ECM interactions are disrupted and for hepatocytes to regain metabolic competency cells are cultured on ECM substrata. The regulation of LETFs in hepatocytes cultured on different ECM has not been studied in detail. We therefore compared two common sources of ECM and evaluated cellular morphology and hepatocyte differentiation by investigating DNA binding activity of LETFs at gene specific promoters and marker genes of hepatic metabolism. Furthermore, we studied testosterone metabolism and albumin synthesis to assess the metabolic competence of cell cultures. Despite significant difference in morphological appearance and except for HNF1ß (p<0.001) most LETFs and several of their target genes did not differ in transcript expression after Bonferroni adjustment when cultured on collagen or Matrigel. Nonetheless, Western blotting revealed HNF1ß, HNF3α, HNF3γ, HNF4α, HNF6 and the smaller subunits of C/EBPα and C/EBPß to be more abundant on Matrigel cultured cells. Likewise, DNA binding activity of HNF3α, HNF3ß, HNF4α, HNF6 and gene expression of hepatic lineage markers were increased on Matrigel cultured hepatocytes. To further investigate hepatic gene regulation, the effects of Aroclor 1254 treatment, e.g. a potent inducer of xenobiotic defense were studied in vivo and in vitro. The gene expression of C/EBP-α increased in rat liver and hepatocytes cultured on collagen and this treatment induced DNA binding activity of HNF4α, C/EBPα and C/EBPß and gene expression of CYP1A1 and CYP1A2 in vivo and in vitro. Taken collectively, two sources of ECM greatly affected hepatocyte morphology, activity of liver enriched transcription factors, hepatic gene expression and metabolic competency that should be considered when used in cell biology studies and drug toxicity testing.

Apoptin as a potential viral gene oncotherapeutic agent.

The use of viruses for treatment of cancer overcomes the bottlenecks of chemotherapy and radiotherapy. Several viruses and their proteins have been evaluated for oncolytic effect. The VP3 protein (apoptin) of chicken anemia virus is one such protein with an inherent ability to lyse cancer and transformed cells while leaving normal cells unharmed. In the present study, the apoptosis inducing potential of VP3 protein of CAV was evaluated in human cervical cancer cell line (HeLa). It was found that in VP3-induced apoptosis, caspase-dependent intrinsic pathway plays an important role with the cleavage of poly (ADP-ribose) polymerase (PARP) and there was no evidence of involvement of death receptor-mediated extrinsic pathway. The results of this study provide intuitive information and strengthen the candidacy of apoptin as a viral oncotherapeutic agent.

In-vitro characterization and evaluation of apoptotic potential of bicistronic plasmid encoding HN gene of Newcastle disease virus and human TNF-α.

The viral gene oncotherapy in combination with cytokines emerges as an exciting strategy for cancer therapy due to its minimal side effects and tumor specificity. HN is the surface protein of NDV which is involved in virus infectivity and is known to kill many cancerous cell types. TNF-α, a multifactorial cytokine has direct anti-tumor activity by activating the extrinsic pathways of apoptosis. In the present study, HN gene of NDV and TNF-α of human were cloned at multiple cloning sites (MCS) 1 and 2 of bicistronic expression vector pVIVO2. Expression pattern of recombinant clone was checked on transcriptional and translational level by RT-PCR, Immunofluorescence assay and flow cytometry. On flow cytometric analysis HN gene expression was found to be 28.30 ± 1.21; 5.22 ± 0.60%, and TNF-α gene expression was found to be 15.44 ± 0.42; 6.51 ± 0.757%, in HeLa cells transfected with pVIVO.nd.hn.hu.tnf and pVIVO2 empty vector control, respectively. These assays confirm that HN and TNF-α act synergistically in the induction of apoptosis in HeLa cells.

Development of dog mammary tumor xenograft in immunosuppressed Swiss albino mice.

Development and study of dog mammary tumour xenograft in immunosuppressed Swiss Albino Mice adds a new dimension in cancer research as dog tumors have many similarities with human tumors regarding progression, histopathology, molecular mechanism, immune response and therapy. Failure of the immune system to recognize and eliminate cancer cells leads to cancer progression and the fight between immune cells and cancer cells has a great role in understanding the mechanism of cancer progression and elimination. Rejection and acceptance of tumour xenograft depends on efficiency of CD4+, CD8+ and NK cell populations. In the present investigation, dog mammary tumor xenograft in cyclosporine-A and gamma-irradiated, immunosuppressed Swiss Albino mice was developed and the immune cell status of graft accepted and rejected mice was assessed. It was observed that all the major immune cells (CD4+, CD8+ and NK cells) play an equal role in tumour rejection.

Recent advances in live cell imaging of hepatoma cells.

Live cell imaging enables the study of dynamic processes of living cells in real time by use of suitable reporter proteins and the staining of specific cellular structures and/or organelles. With the availability of advanced optical devices and improved cell culture protocols it has become a rapidly growing research methodology. The success of this technique relies mainly on the selection of suitable reporter proteins, construction of recombinant plasmids possessing cell type specific promoters as well as reliable methods of gene transfer. This review aims to provide an overview of the recent developments in the field of marker proteins (bioluminescence and fluorescent) and methodologies (fluorescent resonance energy transfer, fluorescent recovery after photobleaching and proximity ligation assay) employed as to achieve an improved imaging of biological processes in hepatoma cells. Moreover, different expression systems of marker proteins and the modes of gene transfer are discussed with emphasis on the study of lipid droplet formation in hepatocytes as an example.

A rat toxicogenomics study with the calcium sensitizer EMD82571 reveals a pleiotropic cause of teratogenicity.

The calcium sensitizer and PDEIII inhibitor EMD82571 caused exencephaly, micrognathia, agnathia and facial cleft in 58% of fetuses. In pursue of mechanisms and to define adverse outcome pathways pregnant Wistar rats were dosed daily with either EMD82571 (50 or 150mg/kg/day) or retinoic acid (12mg/kg/day) on gestational days 6-11 and 6-17, respectively. Hypothesis driven and whole genome microarray experiments were performed with whole embryo, maternal liver, embryonic liver and malformed bone at gestational days 12 and 20. This revealed regulation of genes critically involved in osteogenesis, odontogenesis, differentiation and development and extracellular matrix. Importantly, repression of osteocalcin and members of TGF-ß/BMP signaling hampered osteo- and odontogenesis. Furthermore, EMD82571 impaired neurulation by inhibiting mid hinge point formation to cause neural tube defects. Taken collectively, a molecular rationale for the observed teratogenicity induced by EMD82571 is presented that links molecular initiating events with AOPs.

How useful are clinical liver function tests in in vitro human hepatotoxicity assays?

In preclinical hepatotoxicity testing cell based assays are frequently employed. However, prediction of clinical drug induced liver injury (DILI) remains a major challenge. Here we examined the usefulness of frequently employed markers of hepatocellular injury in cultures of primary human hepatocytes (PHH) in response to treatment with either paracetamol, rifampicin, petadolex and/or amiodarone. The changes in the metabolic competency (urea and albumin) and cellular injury (AST, ALT, ALP, LDH, γGT and succinate dehydrogenase) were determined at therapeutic and above drug concentrations as to evaluate the utility of these markers in in vitro systems. Initially, treatment of PHH with any of the drugs caused a statistically significant reduction in enzyme activities to suggest a switch from basic amino acid metabolism towards induced detoxification. However, treatment for prolonged periods of time caused cytolysis, as evidenced by the significant rise in extracellular LDH and the concomitant increase in ALT and AST activity. Notably, amongst the various endpoints studied, urea was best to demonstrate dose dependent metabolic stress, while other markers of hepatocellular injury were highly variable. Taken collectively, urea measurement proofed to be robust in predicting hepatocellular stress; therefore it should be included in preclinical testing strategies for an improved prediction of DILI.

Canine parvovirus type 2a (CPV-2a)-induced apoptosis in MDCK involves both extrinsic and intrinsic pathways.

The canine parvovirus type 2 (CPV-2) causes an acute disease in dogs. It has been found to induce cell cycle arrest and DNA damage leading to cellular lysis. In this paper, we evaluated the apoptotic potential of the "new CPV-2a" in MDCK cells and elucidated the mechanism of the induction of apoptosis. The exposure of MDCK cells to the virus was found to trigger apoptotic response. Apoptosis was confirmed by phosphatidylserine translocation, DNA fragmentation assays, and cell cycle analysis. Activation of caspases-3, -8, -9, and -12 and decrease in mitochondrial potential in CPV-2a-infected MDCK cells suggested that the CPV-2a-induced apoptosis is caspase dependent involving extrinsic, intrinsic, and endoplasmic reticulum pathways. Increase in p53 and Bax/Bcl2 ratio was also observed in CPV-2a-infected cells.