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Characterization of sorting nexin 3 (SNX3) function

Öyken, Merve
Sorting nexin 3 (SNX3) belongs to the sorting nexins family involved in endocytic trafficking network. SNX3 only has a PX domain, which facilitates binding to the phosphatidyl inositol-3-phosphate on endosomes and has a role in formation of the retromer complex on early endosomes. Endocytosed receptors go through internalization and recycle back to plasma membrane, Trans-Golgi Network or alternatively are degraded in the lysosomes. Earlier, we found that SNX3 messenger RNA (mRNA) is upregulated via alternative polyadenylation in breast cancers. Therefore, we hypothesized that deregulated expression of SNX3 may change the dynamics of endocytic trafficking of membrane receptors in cancer cells. In order to test our hypothesis, we developed different RNA interference (RNAi) models of SNX3 in cancer cell lines and observed that WLS (Wntless, one of the known cargos of SNX3) and EGFR (Epidermal Growth Factor Receptor, possible cargo of SNX3) levels were altered in SNX3 silenced cells compared with the controls. We used proximity-based ligation approach to demonstrate possible interaction between SNX3 and EGFR, used immunostaining to determine subcellular localization of SNX3 and several mutants we generated that showed deregulated ubiquitylation and abnormal subcellular localization. Overall, we showed that SNX3 modulates EGFR protein levels and that ubiquitylation may be important for SNX3 function. Understanding the role of SNX3 and the endocytic trafficking may have future implications for targeted therapies against EGFR.