Abnormal surface glycosylation is a defining feature of a tumor cell, however the functional contribution of glycans to carcinogenesis has been largely ignored. One of the predominant tumor-associated changes is an increase in ?6 sialic acid, a negatively-charged sugar added to selected receptors by the ST6Gal-I glycosyltransferase. In preliminary studies we find for the first time that ST6Gal-I is elevated in pancreatic cancer (PC), and that ST6Gal-I upregulation causes PC cells to acquire behaviors characteristic of cancer stem cells (CSCs), a stem-like cell population inherently metastatic, resistant to cell death, and insensitive to chemotherapeutic drugs. We have also made the landmark discovery that ST6Gal-I upregulation in PC cells induces expression of the CSC-associated transcription factor, Sox9. Sox9 induction is a pivotal initiating event in pancreatic ductal adenocarcinoma. The goals of this application are to establish a role for ST6Gal-I in: (i) CSC-like behaviors directed by a novel ST6Gal-I-NFkB-Sox9 signaling axis; (ii) PC pathogenesis in genetically engineered mice; and (iii) PC cell resistance to gemcitabine, a first-line PC treatment. To achieve these objectives we will employ unique cell model systems, spontaneous PC murine models with forced ST6Gal-I overexpression or deletion, and patient-derived primary tumor and tumor xenograft tissues. This research will extend fundamental knowledge of how sugars regulate tumor cell behavior, and also impact patient care by identifying ST6Gal-I as a marker for resistant cells and potential clinical target for restoring treatment response.
AIM 1 : ST6Gal-I signaling through Sox9 promotes stem-like PC behaviors that drive pathogenesis. Patient-derived primary PC cells, or PC cell lines with forced ST6Gal-I expression or knockdown, will be used to test the hypothesis that ST6Gal-I activity stimulates signaling through NFkB-Sox9 to promote CSC behaviors including self-renewal; tumor spheroid growth; and tumor-initiating potential. Co-expression of ST6Gal-I, activated NFkB and Sox9 will be examined in patient pancreatic adenocarcinoma tissues, and spontaneous PC murine models with pancreas-specific ST6Gal-I knockin or knockout will be utilized to establish a role for ST6Gal-I in PC development and progression.
AIM 2 : ST6Gal-I's contribution to chemoresistance and potential as a therapeutic target. Patient-derived PC cells or cell lines with forced ST6Gal-I expression or knockdown will be treated with gemcitabine to test the hypothesis that ST6Gal-I activity promotes chemoresistance. To show that ST6Gal-Iexpressing cells selectively survive gemcitabine treatment in vivo, ST6Gal-I expression will be quantified in patient-derived tumor xenografts harvested from mice treated with or without gemcitabine. Viable cells will be harvested from the gemcitabine-treated tumor xenografts to obtain an in vivo-selected chemoresistant population. These cells will then be subjected to ST6Gal-I knockdown, followed by gemcitabine treatment, to determine whether gemcitabine sensitivity can be restored in a cell population with known stable resistance.
Pancreatic adenocarcinoma is a particular deadly form of cancer, which has prompted efforts to better understand the molecular biology of this disease, and develop new treatments that target novel pathways. This application describes a very unique glycosylation-dependent mechanism that confers a stem-like, chemoresistant phenotype on pancreatic tumor cells.
| Chakraborty, Asmi; Dorsett, Kaitlyn A; Trummell, Hoa Q et al. (2018) ST6Gal-I sialyltransferase promotes chemoresistance in pancreatic ductal adenocarcinoma by abrogating gemcitabine-mediated DNA damage. J Biol Chem 293:984-994 |
| Holdbrooks, Andrew T; Britain, Colleen M; Bellis, Susan L (2018) ST6Gal-I sialyltransferase promotes tumor necrosis factor (TNF)-mediated cancer cell survival via sialylation of the TNF receptor 1 (TNFR1) death receptor. J Biol Chem 293:1610-1622 |
| Britain, Colleen M; Dorsett, Kaitlyn A; Bellis, Susan L (2017) The Glycosyltransferase ST6Gal-I Protects Tumor Cells against Serum Growth Factor Withdrawal by Enhancing Survival Signaling and Proliferative Potential. J Biol Chem 292:4663-4673 |
| Schultz, Matthew J; Holdbrooks, Andrew T; Chakraborty, Asmi et al. (2016) The Tumor-Associated Glycosyltransferase ST6Gal-I Regulates Stem Cell Transcription Factors and Confers a Cancer Stem Cell Phenotype. Cancer Res 76:3978-88 |
