Regulation of Lysosomal Sorting by Phosphatidylinositol 4-Phosphate, 5-Kinase Type I Gamma i5 and Sorting Nexin 5.

다국어 초록 (Multilingual Abstract)

Phosphoinositide signaling is known to regulate a wide variety of cellular processes, including intracellular trafficking pathways. Phosphoinositide synthesis at specific cellular compartments is regulated by the specific targeting of phosphoinositide modifying enzymes. Phosphatidylinositol 4,5 bisphosphate (PI4,5P2) is primarily synthesized by the type I phosphatidylinositol 4 phosphate 5 kinase (PIPKI) family of enzymes. There are several PIPKI genes and there exist several splice variants for each. The recently discovered PIPKIgammai5 splice variant is localized to intracellular compartments, but its functions are unknown. Initial studies have identified roles for PIPKIgammai5 in promoting the lysosomal sorting of E-cadherin and Epidermal Growth Factor Receptor (EGFR). Therefore, my research focused on how PIPKIgammai5 regulates this pathway. A specific direct interaction was identified between PIPKIgammai5 and Sorting Nexin 5 (SNX5), a PI4,5P2 binding protein that regulates intracellular trafficking. In this pathway, PIPKIgammai5 was found to promote E-cadherin lysosomal degradation, which requires Rab7 function. SNX5 was found to enhance E-cadherin protein levels, but was not required for PIPKIgammai5 function in this pathway. Additionally, PIPKI7i5 and SNX5 were found to be required for EGFR degradation. Furthermore, it was assessed how PI4,5P2 may regulate SNX5 function. Point mutations were identified in the SNX5 PX domain that reduce binding to PI4,5P2 or PIPKIgammai5. However, these mutations did not result in a loss of function for SNX5 function in this pathway. These PIPKIgammai5 studies provide evidence for a novel role for PI4,5P2 in regulating lysosomal sorting. This pathway may be relevant to normal cellular function and potentially, changes in PIPKIgammai5 signaling may alter EGFR and E-cadherin function, resulting in pathological consequences.