Poulami Khan

Curcumin inhibits breast cancer stem cell migration by amplifying the E-cadherin/β-catenin negative feedback loop

IntroductionThe existence of cancer stem cells (CSCs) has been associated with tumor initiation, therapy resistance, tumor relapse, angiogenesis, and metastasis. Curcumin, a plant ployphenol, has several anti-tumor effects and has been shown to target CSCs. Here, we aimed at evaluating (i) the mechanisms underlying the aggravated migration potential of breast CSCs (bCSCs) and (ii) the effects of curcumin in modulating the same.MethodsThe migratory behavior of MCF-7 bCSCs was assessed by using cell adhesion, spreading, transwell migration, and three-dimensional invasion assays. Stem cell characteristics were studied by using flow cytometry. The effects of curcumin on bCSCs were deciphered by cell viability assay, Western blotting, confocal microscopy, and small interfering RNA (siRNA)-mediated gene silencing. Evaluations of samples of patients with breast cancer were performed by using immunohistochemistry and flow cytometry.ResultsHere, we report that bCSCs are endowed with aggravated migration property due to the inherent suppression of the tumor suppressor, E-cadherin, which is restored by curcumin. A search for the underlying mechanism revealed that, in bCSCs, higher nuclear translocation of beta-catenin (i) decreases E-cadherin/beta-catenin complex formation and membrane retention of beta-catenin, (ii) upregulates the expression of its epithelial-mesenchymal transition (EMT)-promoting target genes (including Slug), and thereby (iii) downregulates E-cadherin transcription to subsequently promote EMT and migration of these bCSCs. In contrast, curcumin inhibits beta-catenin nuclear translocation, thus impeding trans-activation of Slug. As a consequence, E-cadherin expression is restored, thereby increasing E-cadherin/beta-catenin complex formation and cytosolic retention of more beta-catenin to finally suppress EMT and migration of bCSCs.ConclusionsCumulatively, our findings disclose that curcumin inhibits bCSC migration by amplifying E-cadherin/beta-catenin negative feedback loop.

Restoration of p53/miR-34a regulatory axis decreases survival advantage and ensures Bax-dependent apoptosis of non-small cell lung carcinoma cells.

Tumor‐suppressive miR‐34a, a direct target of p53, has been shown to target several molecules of cell survival pathways. Here, we show that capsaicin‐induced oxidative DNA damage culminates in p53 activation to up‐regulate expression of miR‐34a in non‐small cell lung carcinoma (NSCLC) cells. Functional analyses further indicate that restoration of miR‐34a inhibits B cell lymphoma‐2 (Bcl‐2) protein expression to withdraw the survival advantage of these resistant NSCLC cells. In such a proapoptotic cellular milieu, where drug resistance proteins are also down‐regulated, p53‐transactivated Bcl‐2 associated X protein (Bax) induces apoptosis via the mitochondrial death cascade. Our results suggest that p53/miR‐34a regulatory axis might be critical in sensitizing drug‐resistant NSCLC cells.

Aspirin Suppresses the Acquisition of Chemoresistance in Breast Cancer by Disrupting an NFκB-IL6 Signaling Axis Responsible for the Generation of Cancer Stem Cells.

Acquired chemoresistance has curtailed cancer survival since the dawn of chemotherapy. Accumulating evidence suggests a major role for cancer stem cells (CSC) in chemoresistance, although their involvement in acquired resistance is still unknown. The use of aspirin has been associated with reduced cancer risk and recurrence, suggesting that the anti-inflammatory drug may exert effects on CSCs. In this study, we investigated the contribution of CSCs to acquired chemoresistance of breast cancer and the avenues for reversing such effects with aspirin. We observed that the residual risk of recurrence was higher in breast cancer patients who had acquired chemoresistance. Treatment of preexisting CSCs with a genotoxic drug combination (5-fluorouracil, doxorubicin, and cyclophosphamide) generated an NFκB-IL6-dependent inflammatory environment that imparted stemness to nonstem cancer cells, induced multidrug resistance, and enhanced the migration potential of CSCs. Treatment with aspirin prior to chemotherapy suppressed the acquisition of chemoresistance by perturbing the nuclear translocation of NFκB in preexisting CSCs. Therefore, disruptions to the NFκB-IL6 feedback loop prevented CSC induction and sensitized preexisting CSCs to chemotherapy. Collectively, our findings suggest that combining aspirin and conventional chemotherapy may offer a new treatment strategy to improve recurrence-free survival of breast cancer patients. Cancer Res; 76(7); 2000-12. ©2016 AACR.

Mithramycin A sensitizes therapy-resistant breast cancer stem cells toward genotoxic drug doxorubicin

Chemotherapy resistance is a major clinical challenge for the management of locally advanced breast cancer. Accumulating evidence suggests a major role of cancer stem cells (CSCs) in chemoresistance evoking the requirement of drugs that selectively target CSCs in combination with chemotherapy. Here, we report that mithramycin A, a known specificity protein (Sp)1 inhibitor, sensitizes breast CSCs (bCSCs) by perturbing the expression of drug efflux transporters, ATP-binding cassette sub-family G, member 2 (ABCG2) and ATP-binding cassette sub-family C, member 1 (ABCC1), survival factors, B-cell lymphoma 2 (Bcl-2) and X-linked inhibitor of apoptosis (XIAP), and, stemness regulators, octamer-binding transcription factor 4 (Oct4) and Nanog, which are inherently upregulated in these cells compared with the rest of the tumor population. In-depth analysis revealed that aberrant overexpression of Sp1 in bCSCs transcriptionally upregulates (1) resistance-promoting genes to protect these cells from genotoxic therapy, and (2) stemness regulators to sustain self-renewal potential of these cells. However, mithramycin A causes transcriptional suppression of these chemoresistant and self-renewal genes by inhibiting Sp1 recruitment to their promoters. Under such antisurvival microenvironment, chemotherapeutic agent doxorubicin induces apoptosis in bCSCs via DNA damage-induced reactive oxygen species generation. Cumulatively, our findings raise the possibility that mithramycin A might emerge as a promising drug in combinatorial therapy with the existing chemotherapeutic agents that fail to eliminate CSCs. This will consequently lead to the improvement of therapeutic outcome for the treatment-resistant breast carcinomas.

Nuclear Matrix Protein SMAR1 Represses c-Fos-mediated HPV18 E6 Transcription through Alteration of Chromatin Histone Deacetylation

Background: HPV18 E6 oncogene represents one of the most promising therapeutic targets for the treatment of HPV-positive tumors. Results: Curcumin-induced SMAR1-HDAC1 recruitment at LCR and E6 region on E6 promoter deacetylates chromatin histones to attenuate c-Fos-mediated E6 transcription to reinstall p53-mediated apoptosis in HPV18-infected cervical cancer. Conclusion: SMAR1 induces E6 repression. Significance: SMAR1 is a repressor of E6-mediated anti-apoptotic network in HPV18-infected cervical cancers. Matrix attachment region (MAR)-binding proteins have been implicated in the transcriptional regulation of host as well as viral genes, but their precise role in HPV-infected cervical cancer remains unclear. Here we show that HPV18 promoter contains consensus MAR element in the LCR and E6 sequences where SMAR1 binds and reinforces HPV18 E6 transcriptional silencing. In fact, curcumin-induced up-regulation of SMAR1 ensures recruitment of SMAR1-HDAC1 repressor complex at the LCR and E6 MAR sequences, thereby decreasing histone acetylation at H3K9 and H3K18, leading to reorientation of the chromatin. As a consequence, c-Fos binding at the putative AP-1 sites on E6 promoter is inhibited. E6 depletion interrupts degradation of E6-mediated p53 and lysine acetyl transferase, Tip60. Tip60, in turn, acetylates p53, thereby restoring p53-mediated transactivation of proapoptotic genes to ensure apoptosis. This hitherto unexplained function of SMAR1 signifies the potential of this unique scaffold matrix-associated region-binding protein as a critical regulator of E6-mediated anti-apoptotic network in HPV18-infected cervical adenocarcinoma. These results also justify the candidature of curcumin for the treatment of HPV18-infected cervical carcinoma.

Aspirin inhibits epithelial-to-mesenchymal transition and migration of oncogenic K-ras-expressing non-small cell lung carcinoma cells by down-regulating E-cadherin repressor Slug

BackgroundCancer metastasis is one of the most common causes of treatment failure and death in cancer patients. It has been acknowledged that aberrant activation of epithelial-to-mesenchymal transition (EMT) program, endows cancer cells with metastatic competence for which E-cadherin switch is a well-established hallmark. Suppression of E-cadherin by its transcriptional repressor Slug is thus a determining factor for EMT. Here, we aimed at discerning (i) the molecular mechanisms that regulate Slug/E-cadherin axis in oncogenic K-ras-expressing non-small cell lung carcinoma (NSCLC) cells, and (ii) the effect of aspirin in modulating the same.MethodsThe migratory behaviour of NSCLC cell line A549 were deciphered by wound healing assay. Further assessment of the molecular mechanisms was done by western blotting, RT-PCR, confocal microscopy, chromatin immunoprecipitation and small interfering RNA (siRNA)-mediated gene silencing.ResultsHere we report that in oncogenic K-ras-expressing A549 cells, Ras/ERK downstream Elk-1 forms p-Elk-1-p300 complex that being directly recruited to SLUG promoter acetylates the same to ensure p65NFκB binding for transcriptional up-regulation of Slug, a transcriptional repressor of E-cadherin. Aspirin inhibits EMT and decelerates the migratory potential of A549 cells by down-regulating Slug and thereby up-regulating E-cadherin. Aspirin impedes activation and nuclear translocation of p65NFκB, essential for this transcription factor being available for SLUG promoter binding. As a consequence, Slug transcription is down-regulated relieving A549 cells from Slug-mediated repression of E-cadherin transcription, thereby diminishing the metastatic potential of these oncogenic Ras-expressing NSCLC cells.ConclusionsCumulatively, these results signify a crucial role of the anti-inflammatory agent aspirin as a novel negative regulator of epithelial-to-mesenchymal transition thereby suggesting its candidature as a promising tool for deterring metastasis of highly invasive K-ras-expressing NSCLC cells.

Sulphur alters NFκB-p300 cross-talk in favour of p53-p300 to induce apoptosis in non-small cell lung carcinoma

Adverse side effects of chemotherapy during cancer treatment have shifted considerable focus towards therapies that are not only targeted but are also devoid of toxic side effects. We evaluated the antitumorigenic activity of sulphur, and delineated the molecular mechanisms underlying sulphur-induced apoptosis in non-small cell lung carcinoma (NSCLC) cells. A search for the underlying mechanism revealed that the choice between the two cellular processes, NFκBp65-mediated survival and p53-mediated apoptosis, was decided by the competition for a limited pool of transcriptional coactivator protein p300 in NSCLC cells. In contrast, sulphur inhibited otherwise upregulated survival signaling in NSCLC cells by perturbing the nuclear translocation of p65NFκB, its association with p300 histone acetylase, and subsequent transcription of Bcl-2. Under such anti-survival condition, induction of p53-p300 cross-talk enhanced the transcriptional activity of p53 and intrinsic mitochondrial death cascade. Overall, the findings of this preclinical study clearly delineated the molecular mechanism underlying the apoptogenic effect of the non-toxic homeopathic remedy, sulphur, in NSCLC cells.

Contribution of nuclear events in generation and maintenance of cancer stem cells: revisiting chemo-resistance

While chemotherapy is often capable of reducing the tumor bulk, disease-free survival of patients is curtailed by recurrence because of chemoresistance. In fact, the cardinal reason of treatment failure can be attributed to chemoresistance, which involves a complex mechanism. In the present scenario, cancer stem cells (CSCs) have been identified to play a pivotal role in chemoresistance. A few reviews have discussed numerous mechanisms of chemoresistance in CSCs and the therapeutic strategies targeting stem cell signaling pathways. References are also there elaborating the applications of therapeutic nanoparticles and epigenetic drugs in targeting CSCs. However, there is a paucity of information in this area that should be explored and addressed. It is a well known fact that the nucleus harbors the entire genome of an organism and is the master regulator of all the genetic and epigenetic programs. In fact, majority of the features of CSCs evolve from cell nucleus. Here we review, the prevailing and emanating concepts of how the key nuclear events like (1) genetic regulation, (2) epigenetic regulation, (3) regulation by microRNAs (miRNA), and (4) DNA repair, can influence CSC properties like (a) induction of EMT (epithelial-mesenchymal transition), (b) self renewal, (c) drug resistance, (d) cellular plasticity, and (e) pluripotency, thereby finally aiding in chemoresistance and cancer recurrence. Information obtained from the discussion will help in revisiting chemoresistance and provide approaches for treating CSCs by targeting nuclear events, thereby improving the prognosis and survival rate of cancer patients in near future.

Proteolytic Networks at the Crossroads of Cancer Cell Life and Death: Cancer Stem Cell Deciding Cell Fate

Over the years, proteases have been implicated in the development of tumors. The proteolytic network, which critically modulates the functioning of a normal cell, is often dysregulated in cancers. In the recent past, the identification of a subpopulation of cancer cells, termed as cancer stem cells (CSCs), has helped gain a better understanding of the complex mechanisms involved in cancer development, progression, as well as recurrence. In this context, it is of considerable importance to comprehend the pivotal role of proteases in regulating the fate of cancer cells via the CSCs. In fact, the proteolytic network influences cancer cell’s fate via CSC and its associated niche, which coordinates the functions of CSCs. In this chapter, we have emphasized on the dynamic role displayed by the proteases in regulating numerous steps of tumorigenesis commencing from tumor initiation, angiogenesis, invasion and metastasis. Apart from this, CSCs also execute a survival mechanism with the help of proteases, upon induction of apoptosis. We have also revisited the mechanisms underlying the contribution of proteases in tumor drug resistance, which ultimately leads to cancer relapse, and the role of CSCs in the same. Similarly, proteases are also intricately involved in inflammation and immune surveillance of CSCs. Given the important role of proteases in carcinogenesis, further development of antiprotease therapeutics may enable better treatment procedures and minimize the risk of recurrence. This chapter has, therefore, epitomized the complex crosstalk involving proteases, CSCs and its niche.

Cancer stem cells, their origin and niche: A search for the therapeutic target

Cancer is a general term to define a group of genetic alterations and the subsequent phenotypic and physiological changes at the cellular level, leading to accelerated death of the host. According to The World Health Organisation (WHO), it is the second leading factor for human deaths globally. Cancer is such a difficult challenge for mankind because of its ability to relapse even after detailed treatments with chemotherapeutic agents and ionizing radiations. This can be explained by the emerging concept of ‘tumor initiating cells’ or ‘cancer stem cells’ (CSCs) which comprise a pluripotent and genomically dynamic subpopulation of the tumor microenvironment, occupying only 0.1%-3% of the total tumor population. Despite their emerging significance in disease progression and recurrence, the origin of these CSCs and their complex interaction with the corresponding CSC niche still remain to be elusive. In this review, we make an attempt to unwind the mystery of the origin of the CSCs as well as focus on the well-established cross-talk mechanisms between the CSCs and their niche components. Lastly, we try to find alternative therapeutic strategies to combat CSC resistance by targeting the various components of the CSC niche. Correspondence to: Das T, Division of Molecular Medicine, Bose Institute, P-1/12 CIT Scheme VII M, Kolkata 700 054, India, Tel: +91-33-2569-3258; Fax: +91-33-2355-3886; E-mail: tanya@jcbose.ac.in