Research Theme
We are a Tumor Glycobiology Lab, which essentially means that we try to understand how tumor-derived glycolipids influence the process of Tumorigenesis. We ask the “What” and “Why” of Gangliosides in Cancer. Gangliosides and specific Ganglioside synthases were reportedly over-expressed in several cancers, and over-expression of specific ganglioside synthase were associated with poor prognosis in terms of low survival. We try to find out “What” is the consequence of sunch an over-expression in the development, growth and progression of tumors, and also try to understand “Why” some of these gangliosides are over-expressed in some cancers. In order to address these complex questions, we take resort of a model Ganglioside, GM2 and its corresponding synthase, GM2-synthase, since GM2 is found to be over-expressed in a number of cancers.
ONGOING RESEARCH PROJECTS
Understanding the role of Ganglioside GM2 in EMT and Metastasis (Project-1)
Previous studies show that GM2 over-expressed and actively shed from cell membrane promotes cancer cell migration, invasion and immune cell dysfunction. However, the role and molecular mechanism played by GM2 in cancer cell metastasis remains elusive. Here, we report that depletion of GM2 from cancer cell significantly reduces their metastatic potential in an in vivo experimental lung metastatic mouse model and increases the overall survivability of mice injected with GM2 knockout cell compared tomice injected with wild type cells expressing GM2. Global transcriptomic analysis from exogenous GM2 treated and nontreated cells reveal that GM2 modulates Hippo transducer YAP-TAZ dependent gene transcription. Additionally, data shows that, GM2 promotes dephosphorylation, expression and nuclear localization of YAP-TAZ. Furthermore, chemical inhibition, siRNA mediated silencing and CRISPR-Cas9 mediated double knockout of YAP-TAZ blocks GM2 mediated modulation of target gene expression, and cancer cell migration, indicating a critical role of YAP-TAZ in GM2-mediated epithelial-mesenchymal transition (EMT). Finally, upstream signaling studies demonstrate that RhoA-Factinand tropomyosin related kinase signaling axis was critically involved in GM2 mediated regulation of Hippo-YAP-TAZ. Collectively, our studies revealed a novel mode of GM2’s action through modulation of the Hippo-YAP-TAZ signaling axis in potentiating cancer cell metastasis.
Deciphering the Transcriptional Regulation of GM2-synthase gene in Cancer (Project-2)
GM2-synthase produces sialic acid-containing glycosphingolipids called gangliosides, and its mRNA overexpression and the gangliosides it generates are linked to tumor progression, migration, and suppression of tumor-specific host immune responses. However, the mechanism underlying GM2- synthase de-repression in renal cell carcinoma (RCC) is poorly understood. Here, we demonstrate that higher GM2-synthase mRNA expression levels in various cancer cells and in human RCC tumors correlate with higher histone acetylation levels (H3K9, H3K14, or both) at region +38/+187 relative to the transcription start site (TSS) of the GM2-synthase gene than in normal kidney epithelial (NKE) cells or healthy adjacent tissues. An increase in GM2-synthase mRNA expression in cells treated with a histone deacetylase (HDAC) inhibitor was accompanied by increased histone acetylation levels at this promoter region. DNA methylation around the TSS was absent in both RCC cell lines and NKE cells. Of note, both the transcription factor Sp1 and corepressor HDAC1 associated with the +38/+187 region when the GM2-synthase gene was repressed in NKE and tumor-adjacent tissues, indicating plausible site-specific repressive roles of HDAC1 and Sp1 in GM2-synthase mRNA expression. Site-directed mutagenesis of the Sp1-binding site within the +38/+187 region relieved repressed luciferase activity of this region by limiting HDAC1 recruitment. Moreover, Sp1 or HDAC1 knockdown increased GM2-synthase transcription, and butyrate-mediated activation of GM2-synthase mRNA expression in SK-RC-45 cells was accompanied by Sp1 and HDAC1 loss from the +37/+187 region. Taken together, we have identified an epigenetic mechanism for the de-repression of the GM2-synthase gene in RCC.
Eriodictyol mediated selective targeting of the TNFR1/FADD/TRADD axis in cancer cells induce cancer cell apoptosis and inhibits tumor progression and metastasis (Project-3)
Although, Eriodictyol, a plant derived flavonoid is well known for its potent anti-inflammatory, only a handful of studies on its potential anti-cancer activities exist. Our study highlights for the first time, the selectivity of eriodictyol as an anti-cancer agent and further attempts to uncover the mechanism underlying its selective cytotoxicty to cancer cells. Here, we show that eriodictyol displayed high selective cytotoxicity in an array of cancer cells, over normal cells, and the inhibition of proliferation was through G2/M phase arrest. Moreover, flow cytometry analysis indicated that eriodictyol induced significant apoptosis in HeLa and HCT-116 as well as in 4T1 and CT-26, in comparison to untransformed WI-38 and NKE cell lines. Further, investigation at the molecular level deciphered that eriodictyol induced apoptosis through expression of the pro-apoptotic components of Death Inducing Signaling Complex (DISC), namely TNFR1, FADD and TRADD in both SK-RC-45 and HeLa. The Co-IP data confirmed direct association of the DISC components post eriodictyol treatment. Additionally, CRISPR/Cas9 mediated knockout of TNFR1 failed to induce apoptosis in HeLa cells in response to eriodictyol, confirming that eriodictyol mediated apoptosis is TNFR1-dependent. While, normal cells (HEK and NKE) neither showed any visible TNFR1 expression, or upregulated TNFR1 upon eriodictyol treatment, tumor cells (HeLa) displayed an elevated TNFR1 expression and also dramatically upregulated the same in response to eriodictyol, thereby, explaining the plausible underlying selectivity of eriodicytol’s anti-cancer activity. Finally, in vivo study in mice implanted with 4T1 breast cancer cells depicted that eriodictyol impedes tumor growth, progression and metastasis without any adverse effect. Thus, our data has identified eriodictyol as a compound with high selectivity index towards cancer cells and defines a novel anti-tumor mechanism of eriodictyol and suggest that it can be further explored for its potential to be used in cancer therapeutics.
Mechanism of ganglioside GM2-mediated regulation of miRs in targeting select oncogenes to mediate tumorigenesis (Project-4)
Extensive studies on the functional role of ganglioside GM2 from our laboratory over the past few years have established its pro-tumorigenic role by promoting tumor migration, invasion and altering cellular survival mechanisms. This study, for the first time, focuses on the differential role of ganglioside GM2 in the regulation of microRNAs in cancer. In silico analysis of Next Generation Sequencing (NGS) data from exogenously administrated GM2 in GM2-deficient cell line, HeLa revealed a subset of up-regulated and down-regulated miRs. A combined transcriptomic as well as small RNA-seq data analysis identified four significantly down-regulated tumor suppressor microRNAs (miRs). Target prediction using bioinformatics, revealed that the 3′-UTR of target oncogenes up-regulated in response to GM2-treatment. So far, GM2 mediated downregulation of the miR and upregulation of the oncogene has been validated by real time PCR and western immunoblotting respectively. This study will aim to define and establish the role of GM2 in the regulation of the specific miR as well as identifying the oncogene as a target and elucidating the functional significance of miR-Oncogene axis in GM2 mediated tumorigenesis.
Research Funding
Council of Scientific and Industrial Research (CSIR), New Delhi
Sanction number: 27(0246)/11/EMR-II
Project Title: “Molecular mechanisms of tumor progression : Role of tumor derived products in mediating tumor cell growth, motility and metastasis.”
Funding Amount : INR 29.00 Lacs
Department of Biotechnology (DBT), New Delhi
Sanction number: BT/PR5338/MED/30/989/2013
Project Title: “Understanding the role of tumor derived glycosphingolipids in carcinogenesis : An in vivo approach.”
Funding Amount : INR 49.00 Lacs
Department of Biotechnology (DBT), New Delhi
Sanction number: BT/469/NE/TBP/2013
Project Title: “Studies on the efficacy of flavonoid and non-flavonoid polyphenols against chronic inflammation induced disease pathogenesis.”
Funding Amount : INR 77.41 Lacs
Department of Science & Technology (DST)-SERB, New Delhi
Sanction number: EMR/2016/001983
Project Title: “A novel role of ganglioside GM2 in the regulation of the Hippo Signaling pathway in tumorigenesis.”
Funding Amount : INR 44.16 Lacs
Indian Council of Medical Research (ICMR), New Delhi
Sanction number: 2019-0137-CMB/adhoc/BMS
Project Title: “Understanding the epigenetic regulation of GM2-synthase gene in cancer.”
Funding Amount : INR 45.30 Lacs
Department of Science & Technology (DST)-SERB, New Delhi
Sanction number: CRG/2021/004623
Project Title: “Mechanism of GM2-mediated regulation of miR-615-5p in targeting oncogenic ID1 in tumorigenesis.”
Funding Amount : INR 52.72 Lacs