Shoukat Dedhar


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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

The interplay of Carbonic Anhydrase IX and the glutamine transporter SLC1A5 in the hypoxic tumor microenvironment (2022)

Carbonic Anhydrase IX (CAIX) is a membrane-bound enzyme that plays a vital role in the pH regulation of hypoxic tumor cells. CAIX is highly expressed in several solid tumors and is an indicator of poor prognosis and response to therapy. Although the importance of CAIX’s role in mediating tumor progression is well-known, the underlying mechanisms remain unclear. To identify the interactors of CAIX in the hypoxic tumor microenvironment, a proteomic analysis was performed using proximity-dependent biotin identification (BioID) and identified metabolic transporters involved in amino acid transport and pH regulation as high confidence interactors. In my thesis, I show that CAIX interacts with the amino acid transporters, SLC1A5; SLC3A2; SLC7A5, and the bicarbonate transporter, SLC4A7. These findings lay a premise for possible dynamic associations of these metabolic transporters with CAIX in the tumor microenvironment to mediate various functions and support tumor progression. In my thesis, I have focused on investigating the interaction of CAIX with SLC1A5, a glutamine (Gln) transporter crucial for supporting tumor growth. Through in-vitro studies, I show that CAIX associates with SLC1A5 in hypoxic cancer cells and regulates Gln uptake in a SLC1A5-depndent manner. Loss of CAIX expression or CAIX activity results in increased Gln transport. I found that the loss of CAIX activity increases cellular ROS, and cells respond by increasing their Gln utilization to synthesize the antioxidant, glutathione (GSH). This helps the cells to maintain redox homeostasis, preventing the lethal effects of oxidative stress and protecting them from cell death. To identify strategies for overcoming resistance to CAIX inhibition, I found that inhibiting the CAIX activity in combination with blocking Gln metabolism or GSH synthesis induces an iron-dependent, oxidative cell death called ferroptosis. Together, these data reveal an important mechanism by which CAIX cooperatively works with SLC1A5 to protect hypoxic cancer cells from oxidative stress and promotes survival. Furthermore, I have demonstrated four different co-targeting strategies that effectively induce ferroptosis in hypoxic cancer cells. In summary, my work has revealed the co-targeting of CAIX activity and Gln metabolism as a potential strategy to effectively treat aggressive, solid tumors.

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Characterization of the mechanisms by which Carbonic Anhydrase IX facilitates tumour growth and metastasis (2015)

The presence of hypoxic microenvironments in solid tumours is a marker of poor prognosis in numerous cancer types, including breast cancer; the second leading cause of cancer-related death.Hypoxia results in an adaptive response in tumour cells through the activation of the transcription factor Hypoxia Inducible Factor-1α (HIF-1α), which stimulates the expression of a large number of genes that contribute to tumour progression. One of the most prominently activated genes is Carbonic Anhydrase IX (CAIX), which facilitates the acidification of the extracellular space and cell invasion by producing protons. Moreover, it assists in keeping the intracellular space neutral through the generation of bicarbonate, which is shuttled into the cytoplasm by bicarbonate transporters, ultimately favouring cell survival. CAIX facilitates breast tumour growth and metastasis; however the exact mechanism remains unknown. The overexpression of CAIX in hypoxic solid tumours, its limited expression in normal tissue and the presence of an extracellular catalytic domain makes this protein an excellent therapeutic target. The intent of this thesis was to unveil the mechanisms by which CAIX facilitates tumour progression, and to characterize novel small molecule inhibitors and antibodies targeting CAIX. It was found that the intracellular (IC) domain of CAIX regulates its catalytic activity, which is required for cell survival, cell invasion and metastasis. The extracellular proteoglycan-like (PG-like) domain of CAIX does not regulate CAIX catalytic activity; however it does modulate cell migration, invasion and metastasis. I identified a role of CAIX in promoting tumour cell invasion through interaction with membrane-bound matrix metalloprotease-14 (MMP-14) and localization in invadopodia. The IC domain of CAIX mediates this interaction and CAIX enzymatic activity appears to regulate the ability of MMP-14 to degrade type I collagen during cell invasion. From the pool of anti-CAIX inhibitors and antibodies characterized in this thesis, the inhibitor U-104 was excellent at blocking CAIX enzymatic activity and has entered phase I clinical trials. Likewise, anti-CAIX antibody MM-26 blocked 50% of CAIX activity and induced cell death in vitro.The work described here provides new insight into the mechanism of CAIX-mediated tumour invasion and metastasis and has identified two new therapeutic strategies for targeting CAIX.

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ILK represses E-cadherin expression by regulating PARP-1 binding to the Snail promoter (2011)

No abstract available.

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Exploring the role of chemotherapy-induced anastasis in triple-negative breast cancer (2019)

Triple-negative breast cancer (TNBC), is an aggressive and metastatic variant that lacks relevant treatment-targeted receptors. In addition, resistance to cytotoxic chemotherapeutic drugs is a common attribute of these cells, although little is known about how it is acquired. My hypothesis is that “Anastasis”, a reversal of end-stage apoptosis demarked by caspase-3 (Cas3) cleavage plays a role in drug resistance and cancer progression. Anastasis has been observed in many cell types, including cancer, however, its role in response to apoptotic stimuli is poorly understood, especially concerning its induction by clinically relevant chemotherapy agents. To test the above hypothesis, I used a GFP-tagged Cas3 reporter in order to measure DEVDase (pro-caspase) activity, indicating the level of Cas3 activation indirectly. This allowed for the selection of living, apoptotic cells using fluorescent activated cell sorting (FACS), whereby post-anastatic cells survived chemotherapy-induced apoptosis upon drug removal. While these cells do not appear phenotypically different, it was shown that they are more resistant to the original treatment, possess increased DNA damage, are more invasive, migratory, and metastatic, as well as more metabolically robust. Mechanistically, I determined that these cells produce a truncated caspase-3 isoform (Cas3s) that prevents apoptosome assembly early in the recovery stages of anastasis and long after its completion. Additionally, levels of native Cas3 remained unchanged during recovery and a decrease in Cas3 activation was observed upon treatment. Furthermore, a phenotypic characteristic of the post-anastatic cells revealed a significant up-regulation of epithelial-mesenchymal transition (EMT) and hypoxia stress markers. Inhibition of one of the up-regulated proteins, integrin-linked kinase (ILK) resulted in re-sensitization to chemotherapy treatment, a decrease in migration, as well as a dampening of the enhanced metabolic activity. These findings support a potential role for anastasis as a novel mechanism for resistance in TNBC and provides mechanistic insight into its role in tumor cell biology, that which has not been previously described.

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The Roles of Integrin-Linked Kinase at the Centrosome and its Regulation of Microtubule Dynamics (2012)

Integrin-linked kinase (ILK) is both a scaffolding protein and a serine/threonine kinase that localizes to the focal adhesions. It interacts with the cytoplasmic domain of the β1-integrin subunit and acts as a hub for the localization of several actin cytoskeletal and signaling proteins resulting in the transduction of signals from cell-matrix interactions and growth factors into the cell interior. These signaling cascades go on to regulate important cellular processes such as cell migration, survival and proliferation. ILK has a second cellular localization at the centrosomes, where it regulates mitotic spindle organization and the interaction between ch-TOG, TACC3 and Aurora A, which is important for their function in regulating microtubule dynamics and spindle organization. However, the specific role of ILK's kinase activity, separate from a possible scaffolding role, in spindle organization is unclear. For this study, I attempted to characterize the spindle defect caused by QLT-0267, a small molecule inhibitor that is highly selective for ILK kinase activity. Treatment of HeLa cells with 10 μM QLT-0267 is known to result in a disorganized mitotic spindle that appeared arrested in a prometaphase-like phenotype. Here, I show that QLT-0267 exposure resulted in an increase in tension across sister centromeres aligned between two poles, suggesting a possible effect on spindle microtubule dynamics. Treatment with QLT-0267 was also associated with slower microtubule regrowth after depolymerization and the presence of a more stable population of microtubules in the mitotic spindle as evidenced by higher levels of acetylated α-tubulin. To further assess the role of ILK in regulating microtubule dynamics, the parameters of microtubule dynamic instability were measured in both QLT-0267-treated HeLa cells and ILK overexpressing HeLa cells. QLT-0267 appeared to dampen microtubule dynamic instability, while ILK overexpression enhanced it. ILK overexpression was also associated with decreased sensitivity to paclitaxel, a chemotherapeutic agent that stabilizes microtubule dynamics.Taken together, the results suggest a role for ILK's kinase activity in regulating microtubule dynamics. Finally, this study reports a novel mechanism of action for the small molecule inhibitor QLT-0267, which dampens microtubule dynamics and should be taken into consideration when designing future uses for the compound.

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Integrin-linked kinase is an essential mediator of ERG-induced epithelial-to-mesenchymal transition in prostate cancer models (2011)

Approximately 50% of human prostate cancers carry a gene fusion involving the 5' untranslated region of TMPRSS2, an androgen-regulated gene, and the protein-coding sequences of ERG, which encodes an ETS transcription factor. Exogenous expression of ERG in human prostatic epithelial cell lines (PrECs) promotes phenotypic changes associated with epithelial-to-mesenchymal transition (EMT), a process implicated in the invasion and metastasis of carcinomas. To gain insight into the biological mechanism by which ERG promotes EMT, I used two immortalized PrECs stably infected with a lentiviral vector expressing a Flag epitope-tagged ERG3 (fERG-PrECs). qRT-PCR and Western blotting show that integrin-linked kinase (ILK) mRNA and protein levels are increased in fERG-PrECs. The mesenchymal markers and downstream effectors of ILK, LEF-1 and Snail, are also upregulated in fERG-PrECs. Depletion of ILK expression by siRNA or inhibition of its activity with a highly selective small molecule inhibitor, QLT-0267, results in a substantial decrease in ERG-mediated upregulation of Snail and LEF-1. Furthermore, I show that inhibition of ILK activity impairs the in vitro invasive properties and suppresses the anchorage-independent growth of fERG-PrECs. In conclusion, I have provided novel insights into critical pathways by which aberrant ERG expression may promote prostate cancer progression. In particular, I presented evidence to support the hypothesis that ERG-mediated oncogenesis in prostate cancer involves activation of ILK signaling, leading to key cancer-promoting phenotypic effects, such as EMT.

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