Abstract
Background: By exploiting the canonical function of the sodium iodide symporter (NIS), ablative radioiodide therapy is an effective treatment for thyroid cancer and has been hypothesised as a viable treatment for breast cancer. However, up to a quarter of patients are unable to accumulate sufficient radioiodide for effective treatment due to decreased expression of NIS and/or reduced plasma membrane localisation. Currently, the regulation of NIS trafficking and its localisation at the plasma membrane is ill-defined.
Methods: To identify novel NIS-interactors, and unravel the mechanism of NIS trafficking, mass spectrometry analysis was performed on proteins co-immunoprecipitating with lentivirally expressed NIS in cell plasma membrane extracts. To determine the biological impact of these putative interactors on NIS, siRNA knockdown of the top shortlisted interactors was followed by radioiodide uptake assays. Further, to validate interactors that altered NIS function, co-immunoprecipitation and proximity ligation assays were completed.
Results: NIS activity was significantly altered by ADP-ribosylation factor 4 (ARF4) and valosin containing protein (VCP) in thyroid and breast cancer cell lines stably-expressing NIS. ARF4 downregulation significantly decreased radioiodide uptake by 75% and 44%, and VCP downregulation increased radioiodide uptake by 71% and 56%, in the thyroid and breast cell lines, respectively. In contrast, ARF4 overexpression significantly increased radioiodide uptake by 89% and 43%, and VCP overexpression decreased radioiodide uptake by 52% and 38%, in thyroid and breast cell lines, respectively. Through both co-immunoprecipitation and proximity ligation assays it was confirmed that NIS interacts with ARF4 and VCP. Analysis of TCGA data from N = 58 matched papillary thyroid cancers revealed ARF4 is significantly repressed and VCP highly upregulated in thyroid cancer, providing a new putative explanation for repressed NIS function.
Conclusion: These studies elucidating the regulation of NIS localisation have identified two novel potential therapeutic targets for enhancing radioiodide uptake in patients who are radioiodide-refractory.
Methods: To identify novel NIS-interactors, and unravel the mechanism of NIS trafficking, mass spectrometry analysis was performed on proteins co-immunoprecipitating with lentivirally expressed NIS in cell plasma membrane extracts. To determine the biological impact of these putative interactors on NIS, siRNA knockdown of the top shortlisted interactors was followed by radioiodide uptake assays. Further, to validate interactors that altered NIS function, co-immunoprecipitation and proximity ligation assays were completed.
Results: NIS activity was significantly altered by ADP-ribosylation factor 4 (ARF4) and valosin containing protein (VCP) in thyroid and breast cancer cell lines stably-expressing NIS. ARF4 downregulation significantly decreased radioiodide uptake by 75% and 44%, and VCP downregulation increased radioiodide uptake by 71% and 56%, in the thyroid and breast cell lines, respectively. In contrast, ARF4 overexpression significantly increased radioiodide uptake by 89% and 43%, and VCP overexpression decreased radioiodide uptake by 52% and 38%, in thyroid and breast cell lines, respectively. Through both co-immunoprecipitation and proximity ligation assays it was confirmed that NIS interacts with ARF4 and VCP. Analysis of TCGA data from N = 58 matched papillary thyroid cancers revealed ARF4 is significantly repressed and VCP highly upregulated in thyroid cancer, providing a new putative explanation for repressed NIS function.
Conclusion: These studies elucidating the regulation of NIS localisation have identified two novel potential therapeutic targets for enhancing radioiodide uptake in patients who are radioiodide-refractory.
| Original language | English |
|---|---|
| Article number | O6 |
| Pages (from-to) | 4-4 |
| Number of pages | 1 |
| Journal | Thyroid Research |
| Volume | 10 |
| Issue number | Suppl 2 |
| DOIs | |
| Publication status | Published - 19 Sept 2017 |
| Event | 65th British Thyroid Association Annual Meeting - London, United Kingdom Duration: 16 May 2017 → 16 May 2017 |
