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UBC Theses and Dissertations

The role of sodium hydrogen exchanger isoform 5 (NHE5) in integrin β1 trafficking Rajendran, Vinotheni


Proper targeting of the receptors to their cellular compartments is essential for their function. This is achieved by vesicular trafficking, which is a highly regulated cellular process. One of the key determinants for this process is organellar pH, which is regulated by various ion transporters. In this thesis, I showed that sodium hydrogen exchanger isoform 5 (NHE5), a neuron-enriched ion transporter that is aberrantly expressed in recycling endosomes of C6 rat glioma cells and acidifies the lumen, regulates the trafficking of integrin β1 (Intβ1), a major class of cell adhesion receptors. Depletion of NHE5 expression in C6 glioma cells resulted in impaired integrin-mediated cell adhesion and spreading. Using various biochemical and immunofluorescence assays, I found that NHE5 influences endocytic recycling and degradation of Intβ1. Interestingly, a reduction in the apparent molecular weight of Intβ1 was observed in NHE5-knockdown cells. Through various enzymatic and lectin pull-down assays, I showed that NHE5 affects the sialylation of Ιntβ1. Using biochemical assays, I, further demonstrated that Intβ1 is further sialylated (‘extra-sialylated’) during retrograde trafficking through the trans-Golgi Network, in addition to their canonical sialylation in the secretory pathway and this process is mediated by NHE5. Results from this thesis and previous studies led me to propose that NHE5 to be forming a distinct and previously unidentified endosomal compartment, where it sorts and recycles a subset of receptors. By doing so, NHE5 modulates cell attachment, spreading, polarity and migration. Future studies will elucidate how NHE5 modulates retrograde trafficking and sialylation of Intβ1, and influences cell migration, tumor invasion and metastasis of gliomas and other cancers. In summary, this work provides insight into the role of NHE5 in mediating important cellular processes such as cell adhesion, spreading, polarity and migration of C6 glioma.

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