Sialyltransferase ST6GAL-1 mediates resistance to chemoradiation in rectal cancer

Mary Smithson,Regina Irwin,Gregory Williams,Katie L Alexander,Lesley E Smythies,Marie Nearing,M Chandler Mcleod,Sameer Al Diffalha,Susan L Bellis,Karin M Hardiman

doi:10.1016/j.jbc.2022.101594

Mary Smithson, Regina Irwin + Show 8 more

Open Access

https://doi.org/10.1016/j.jbc.2022.101594

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Abstract

Locally advanced rectal cancer is typically treated with chemoradiotherapy followed by surgery. Most patients do not display a complete response to chemoradiotherapy, but resistance mechanisms are poorly understood. ST6GAL-1 is a sialyltransferase that adds the negatively charged sugar, sialic acid (Sia), to cell surface proteins in the Golgi, altering their function. We therefore hypothesized that ST6GAL-1 could mediate resistance to chemoradiation in rectal cancer by inhibiting apoptosis. Patient-derived xenograft and organoid models of rectal cancer and rectal cancer cell lines were assessed for ST6GAL-1 protein with and without chemoradiation treatment. ST6GAL-1 mRNA was assessed in untreated human rectal adenocarcinoma by PCR assays. Samples were further assessed by Western blotting, Caspase-Glo apoptosis assays, and colony formation assays. The presence of functional ST6GAL-1 was assessed via flow cytometry using the Sambucus nigra lectin, which specifically binds cell surface α2,6-linked Sia, and via lectin precipitation. In patient-derived xenograft models of rectal cancer, we found that ST6GAL-1 protein was increased after chemoradiation in a subset of samples. Rectal cancer cell lines demonstrated increased ST6GAL-1 protein and cell surface Sia after chemoradiation. ST6GAL-1 was also increased in rectal cancer organoids after treatment. ST6GAL-1 knockdown in rectal cancer cell lines resulted in increased apoptosis and decreased survival after treatment. We concluded that ST6GAL-1 promotes resistance to chemoradiotherapy by inhibiting apoptosis in rectal cancer cell lines. More research will be needed to further elucidate the importance and mechanism of ST6GAL-1-mediated resistance.

Highlights

Rectal cancer and other GI cancers, including gastric and esophageal cancers, are treated with chemoradiation including 5-fluorouracil (5-FU), or its oral equivalent capecitabine, and radiation daily for 6 weeks followed by surgery
In order to assess whether the increased ST6GAL-1 was functional, treated and untreated cells were assessed for ST6GAL-1 activity using a Fluorescein isothiocyanate (FITC)-labeled Sambucus nigra (SNA) lectin which binds to the sialic acid (Sia) on cell surface proteins that have been added by ST6GAL-1 in the Golgi
We found that ST6GAL-1 and Sia on cell surface proteins are increased after chemoradiation in rectal cancer cell lines, rectal cancer-derived organoids, and Patient-derived xenograft (PDX) models using western, flow cytometry, immunostaining, and immunoprecipitation

Summary

INTRODUCTION

Rectal cancer and other GI cancers, including gastric and esophageal cancers, are treated with chemoradiation including 5-fluorouracil (5-FU), or its oral equivalent capecitabine, and radiation daily for 6 weeks followed by surgery. Around 15% of patients are complete responders to pre-operative chemoradiotherapy and clinical trials managing these complete responders without surgery are ongoing [2] While this new management is promising, most patients are not complete responders and investigations into the mechanisms of resistance to treatment are vital [3,4]. We subsequently used rectal cancer cell lines to assess functional ST6GAL-1 protein after chemoradiotherapy and found that it was increased. We showed that ST6GAL-1 mediates therapeutic resistance in rectal cancer by decreasing apoptosis and TNFR1 as the potential target of this decrease. Taken together, these studies implicate ST6GAL-1 as a potentially important mediator of resistance to chemoradiation in rectal cancer

RESULTS

DISCUSSION

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