Advisory Committee Chair
Advisory Committee Members
Date of Award
Degree Name by School
Master of Science (MS) School of Medicine
Locally advanced rectal cancer is treated with chemoradiotherapy followed by surgery. Most patients do not have a complete response to chemoradiotherapy, and the resistance mechanisms are poorly understood. We investigated the role of ST6GAL-1 in therapeutic resistance. ST6GAL-1 is a sialytransferase that adds the negatively charged sugar, sialic acid (Sia), to cell surface proteins in the Golgi altering their function. We hypothesized that ST6GAL-1 mediates resistance to chemoradiation in rectal cancer by inhibiting apoptosis. Patient derived xenograft (PDX) and organoid models of rectal cancer as well as rectal cancer cell lines SW837 and SW620 were assessed for ST6GAL-1 protein with and without chemoradiation treatment. ST6GAL-1 mRNA was assessed in untreated human rectal adenocarcinoma by polymerase chain reaction (PCR). A TMA (tissue microarray) of rectal cancer patients was created from pre-and-post treatment biopsies and evaluated by staining for ST6GAL-1. Rectal cancer cell lines were transduced with a control (CV) or shST6GAL-1 vector (KD). Samples were assessed using western blotting, Caspase 3/7 apoptosis assay, and colony formation assay. The presence of functional ST6GAL-1 was assessed via flow cytometry using the Sambucus Nigra (SNA) lectin, which specifically binds cell surface ,6-linked Sia, and via lectin precipitation. SW620 KD cells were iv treated with extracellular vesicles collected from SW620 cells and evaluated by western, flow cytometry, and fluorescent staining to evaluate ability to transfer between cells. In PDX models of rectal cancer, ST6GAL-1 protein was increased after chemoradiation in a subset of samples. The TMA showed an increase of ST6GAL-1 in 7 of 17 patients after chemoradiation. Rectal cancer cell lines demonstrated increased ST6GAL-1 protein and cell surface Sia after chemoradiation. ST6GAL-1 also increased in rectal cancer organoids after treatment. KD of ST6GAL-1 in rectal cancer cell lines resulted in increased apoptosis and decreased survival after treatment. TNFR1 (tumor necrosis factor receptor 1) was identified as a mechanism of apoptosis. Lastly, functional ST6GAL-1 was shown to be transferable to KD cells by ECVs. ST6GAL-1 promotes resistance to chemoradiotherapy by inhibiting apoptosis in rectal cancer. More research is needed to further elucidate the importance and mechanism of ST6GAL-1 mediated resistance.
Smithson, Mary, "Sialylation as a Novel Mechanism of Radiation Resistance in Rectal Cancer" (2021). All ETDs from UAB. 525.