Anindya Goswami

The Tumor Suppressor Par-4 Activates an Extrinsic Pathway for Apoptosis

Prostate apoptosis response-4 (Par-4) is a proapoptotic protein with intracellular functions in the cytoplasm and nucleus. Unexpectedly, we noted Par-4 protein is spontaneously secreted by normal and cancer cells in culture, and by Par-4 transgenic mice that are resistant to spontaneous tumors. Short exposure to endoplasmic reticulum (ER) stress-inducing agents further increased cellular secretion of Par-4 by a brefeldin A-sensitive pathway. Secretion occurred independently of caspase activation and apoptosis. Interestingly, extracellular Par-4 induced apoptosis by binding to the stress response protein, glucose-regulated protein-78 (GRP78), expressed at the surface of cancer cells. The interaction of extracellular Par-4 and cell surface GRP78 led to apoptosis via ER stress and activation of the FADD/caspase-8/caspase-3 pathway. Moreover, apoptosis inducible by TRAIL, which also exerts cancer cell-specific effects, is dependent on extracellular Par-4 signaling via cell surface GRP78. Thus, Par-4 activates an extrinsic pathway involving cell surface GRP78 receptor for induction of apoptosis.

Phosphorylation of Par-4 by protein kinase A is critical for apoptosis

ABSTRACT Despite distinct dissimilarities, diverse cancers express several common protumorigenic traits. We present here evidence that the proapoptotic protein Par-4 utilizes one such common tumorigenic trait to become selectively activated and induce apoptosis in cancer cells. Elevated protein kinase A (PKA) activity noted in cancer cells activated the apoptotic function of ectopic Par-4 or its SAC (selective for apoptosis induction in cancer cells) domain, which induces apoptosis selectively in cancer cells and not in normal or immortalized cells. PKA preferentially phosphorylated Par-4 at the T155 residue within the SAC domain in cancer cells. Moreover, pharmacological-, peptide-, or small interfering RNA-mediated inhibition of PKA activity in cancer cells resulted in abrogation of both T155 phosphorylation and apoptosis by Par-4. The mechanism of activation of endogenous Par-4 was similar to that of ectopic Par-4, and in response to exogenous stimuli, endogenous Par-4 induced apoptosis by a PKA- and phosphorylated T155-dependent mechanism. Enforced elevation of PKA activity in normal cells resulted in apoptosis by the SAC domain of Par-4 in a T155-dependent manner. Together, these observations suggest that selective apoptosis of cancer cells by the SAC domain of Par-4 involves phosphorylation of T155 by PKA. These findings uncover a novel mechanism engaging PKA, a procancerous activity commonly elevated in most tumor cells, to activate the cancer selective apoptotic action of Par-4.

The Phosphoinositide 3-Kinase/Akt1/Par-4 Axis: A Cancer-Selective Therapeutic Target

Activation of the phosphoinositide 3-kinase (PI3K)/Akt cell survival pathway in many cancers makes it an appealing target for therapeutic development. However, because this pathway also has an important role in the survival of normal cells, tactics to achieve cancer selectivity may prove important. We recently showed that the cancer-selective proapoptotic protein Par-4 is a key target for inactivation by PI3K/Akt signaling. Additionally, we found that Par-4 participates in mediating apoptosis by PTEN, the tumor suppressor responsible for blocking PI3K/Akt signaling. As a central player in cancer cell survival, Par-4 may provide a useful focus for the development of cancer-selective therapeutics.

Suppression of PTEN Expression Is Essential for Antiapoptosis and Cellular Transformation by Oncogenic Ras

Ras is one of the most commonly mutated oncogenes in the array of human cancers. The mechanism by which Ras induces cellular transformation is, however, not fully elucidated. We present here evidence that oncogenic Ras suppresses the expression of the tumor suppressor phosphatase and tensin homologue deleted from chromosome 10 (PTEN), and this action of oncogenic Ras is mediated by the Raf-mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK pathway via up-regulation of c-Jun. Jun(+/+) cells undergo cellular transformation by oncogenic Ras, and restoration of wild-type PTEN, but not a phosphate-defective mutant of PTEN, induces apoptosis in these cells. Conversely, in Jun(-/-) cells, oncogenic Ras neither suppresses PTEN nor causes transformation, but rather it induces PTEN-dependent apoptosis. An apoptotic response to oncogenic Ras in Jun(-/-) cells can be prevented by suppressing PTEN expression. These findings imply that oncogenic Ras suppresses the apoptotic gene PTEN via the Raf-MEK-ERK-c-Jun pathway to induce antiapoptosis and cellular transformation. Together, our findings identify a novel molecular interface between the oncogenic and tumor suppressor pathways that regulates cellular transformation and survival.

A novel MMP-2 inhibitor 3-azidowithaferin A (3-azidoWA) abrogates cancer cell invasion and angiogenesis by modulating extracellular Par-4.

Background Withaferin A, which is a naturally derived steroidal lactone, has been found to prevent angiogenesis and metastasis in diverse tumor models. It has also been recognized by different groups for prominent anti-carcinogenic roles. However, in spite of these studies on withanolides, their detailed anti-metastatic mechanism of action remained unknown. The current study has poised to address the machinery involved in invasion regulation by stable derivative of Withaferin A, 3-azido Withaferin A (3-azidoWA) in human cervical HeLa and prostate PC-3 cells. Methods and Principal Findings Sub-toxic concentration of 3-azidowithaferin A (3-azido WA) inhibited cancer cell motility and invasion in wound healing and Boyden chamber invasion by suppressing MMP-2 activity in gelatin zymography and its expression has proved to be a major obstacle in chemo-sensitivity. We have uncovered a novel mechanism of 3-azidoWA induced extracellular pro-apoptotic candidate tumor suppressor Par-4 protein stimulation in conditioned media and also noticed a concomitant marked reduction in pAkt and pERK signaling by immunoblot analysis. Furthermore, our zymography results suggest 3-azidoWA induced MMP-2 inhibition was mediated through secretory Par-4. The inhibition of apoptosis by 3-azidoWA could not restore MMP-2 gelatinase activity. In addition to this, our in vivo animal experiments data showed 3-azidoWA abrogated neovascularisation in dose dependent manner in mouse Matrigel plug assay. Conclusion/Significance For this report, we found that 3-azidoWA suppressed motility and invasion of HeLa and PC-3 cells in MMP-2 dependent manner. Our in vitro result strongly suggests that sub-toxic doses of 3-azidoWA enhanced the secretion of extracellular Par-4 that abolished secretory MMP-2 expression and activity. Depletion of secretory Par-4 restored MMP-2 expression and invasion capability of HeLa and PC-3 cells. Further, our findings implied that 3-azidoWA attenuated internal phospho-ERK and phospho-Akt expression in a dose dependent manner might play a key role in inhibition of mouse angiogenesis by 3-azidoWA.

Par-4 Binds to Topoisomerase 1 and Attenuates Its DNA Relaxation Activity

The regulation of DNA relaxation by topoisomerase 1 (TOP1) is essential for DNA replication, transcription, and recombination events. TOP1 activity is elevated in cancer cells, yet the regulatory mechanism restraining its activity is not understood. We present evidence that the tumor suppressor protein prostate apoptosis response-4 (Par-4) directly binds to TOP1 and attenuates its DNA relaxation activity. Unlike camptothecin, which binds at the TOP1-DNA interface to form cleavage complexes, Par-4 interacts with TOP1 via its leucine zipper domain and sequesters TOP1 from the DNA. Par-4 knockdown by RNA interference enhances DNA relaxation and gene transcription activities and promotes cellular transformation in a TOP1-dependent manner. Conversely, attenuation of TOP1 activity either by RNA interference or Par-4 overexpression impedes DNA relaxation, cell cycle progression, and gene transcription activities and inhibits transformation. Collectively, our findings suggest that Par-4 serves as an intracellular repressor of TOP1 catalytic activity and regulates DNA topology to suppress cellular transformation.

Design and synthesis of novel N,N′-glycoside derivatives of 3,3′-diindolylmethanes as potential antiproliferative agents

A library of 34 compounds containing the DIM core have been synthesized and tested for their anticancer efficacy by measuring their cytotoxicity to cancer cell lines A549, HeLa and MCF-7. Some of the selected derivatives were N-glycosylated to increase their efficacy. Compound 7d, an N-glycosylated DIM derivative, was found to be effective at 1.3, 0.3 and 0.9 μmol concentrations against A549, HeLa and MCF-7, respectively. Immunochemistry studies revealed that it could induce apoptosis by upregulating a pro-apoptotic protein Par-4 and concomitantly diminishing the expression of pro-survival proteins Bcl-2 and GRP78. Flow cytometry studies showed that the compound arrested cells in the G1 phase of the cell cycle and significantly abrogated the motility of HeLa cells. Computer docking simulations of 7d with GRP78 suggested its involvement in two H-bonds with Asp78, two H-bonds with Arg290, one with Arg367, and one water mediated H-bond interaction. The interaction patterns also demonstrated that the presence of bromide in the vicinity (within 3.5 A) of Lys294 generates the possibility of a halogen bond, which may also contribute in providing some extra stability to the complex. Hence, compounds of this class will be useful for the design of new anticancer agents.

Par-4 dependent modulation of cellular β-catenin by medicinal plant natural product derivative 3-azido Withaferin A

Here, we provide evidences that natural product derivative 3‐azido Withaferin A (3‐AWA) abrogated EMT and invasion by modulating β‐catenin localization and its transcriptional activity in the prostate as well as in breast cancer cells. This study, for the first time, reveals 3‐AWA treatment consistently sequestered nuclear β‐catenin and augmented its cytoplasmic pool as evidenced by reducing β‐catenin transcriptional activity in these cells. Moreover, 3‐AWA treatment triggered robust induction of pro‐apoptotic intracellular Par‐4, attenuated Akt activity and rescued Phospho‐GSK3β (by Akt) to promote β‐catenin destabilization. Further, our in vitro studies demonstrate that 3‐AWA treatment amplified E‐cadherin expression along with sharp downregulation of c‐Myc and cyclin D1 proteins. Strikingly, endogenous Par‐4 knock down by siRNA underscored 3‐AWA mediated inhibition of nuclear β‐catenin was Par‐4 dependent and suppression of Par‐4 activity, either by Bcl‐2 or by Ras transfection, restored the nuclear β‐catenin level suggesting Par‐4 mediated β‐catenin regulation was not promiscuous. In vivo results further demonstrated that 3‐AWA was effective inhibitor of tumor growth and immunohistochemical studies indicated that increased expression of total β‐catenin and decreased expression of phospho‐β‐catenin and Par‐4 in breast cancer tissues as compared to normal breast tissue suggesting Par‐4 and β‐catenin proteins are mutually regulated and inversely co‐related in normal as well as cancer condition. Thus, strategic regulation of intracellular Par‐4 by 3‐AWA in diverse cancers could be an effective tool to control cancer cell metastasis. Conclusively, this report puts forward a novel approach of controlling deregulated β‐catenin signaling by 3‐AWA induced Par‐4 protein.

Design and Synthesis of Antitumor Heck-Coupled Sclareol Analogues: Modulation of BH3 Family Members by SS-12 in Autophagy and Apoptotic Cell Death.

Sclareol, a promising anticancer labdane diterpene, was isolated from Salvia sclarea. Keeping the basic stereochemistry-rich framework of the molecule intact, a method for the synthesis of novel sclareol analogues was designed using palladium(II)-catalyzed oxidative Heck coupling reaction in order to study their structure-activity relationship. Both sclareol and its derivatives showed an interesting cytotoxicity profile, with 15-(4-fluorophenyl)sclareol (SS-12) as the most potent analogue, having IC50 = 0.082 μM against PC-3 cells. It was found that SS-12 commonly interacts with Bcl-2 and Beclin 1 BH3 domain proteins and enhances autophagic flux by modulating autophagy-related proteins. Moreover, inhibition of autophagy by autophagy inhibitors protected against SS-12-induced apoptosis. Finally, SS-12 effectively suppressed tumor growth in vivo in Ehrlichs ascitic and solid Sarcoma-180 mouse models.

Preparation, characterization and toxicological investigation of copper loaded chitosan nanoparticles in human embryonic kidney HEK-293 cells

Metallic nanoparticles often attribute severe adverse effects to the various organs or tissues at the molecular level despite of their applications in medical, laboratory and industrial sectors. The present study highlights the preparation of copper adsorbed chitosan nanoparticles (CuCSNPs), its characterization and validation of cytotoxicity in human embryonic kidney HEK-293 cells. Particle size of the CuCSNPs was determined by using Zetasizer and the copper loading was quantified with the help of ICP/MS. Further characterization of CuCSNPs was carried out by FT-IR analysis to determine the formation of nanoparticles and SEM was conducted for the morphological analysis of the CuCSNPs. The CuCSNPs exhibited pronounced cytotoxic effects towards HEK-293 cells as analyzed by MTT assay. Moreover, the CuCSNPs inhibited the colony formation and induced nuclear damage at the dose of 100 μg/mL, much more effectively than the in built control copper sulfate (CuSO4). At the molecular level, the CuCSNPs were found to be triggering reactive oxygen species (ROS), activating effector caspases and subsequent PARP cleavage to induce cell death in HEK-293 cells.