Role of the Endocytic protein Epsin in cell signaling in Health and Disease
Epsins are a conserved family of endocytic adaptors characterized by an ENTH (Epsin N- Terminal Homology) domain and an unstructured C terminus. The ENTH domain binds to phosphatidyl inositol (4,5) bisphosphate at the plasma membrane and contributes to endocytosis by inducing membrane curvature. The C terminus has endocytic motifs and its function is to recruit endocytic machinery via protein-protein interactions. Our lab showed that, apart from its endocytic function, Epsin has a signaling function as an inhibitor of Rho GTPase Activating Proteins (RhoGAPs) mediated by its ENTH domain. This signaling function was established to be essential for cell polarity-dependent processes such as cell migration and dependent on the RhoGAP domain-containing proteins RalBP1 and Ocrl1. It should be noted that RalBP1 (and Epsin) is found upregulated in several cancers, while Ocrl1 deficiency leads to a lethal developmental disease known as Lowe syndrome (LS). We discovered RhoGTPase deregulation and cell migration abnormalities in both these disease states. This work explores the mechanism underlying the two disease states as dependent of the Epsin-RhoGAP interaction. Epsin and RalBP1 overexpression in vitro leads to enhanced cell migration as seen in invasive cancers. Importantly, though the ENTH domain signaling function is essential and sufficient for sustaining cell migration, only full length Epsin overexpression could enhance cell invasion. So, we studied the role of the C terminus in sustaining enhanced cell migration/invasion. We hypothesized that Epsin ENTH domain and C terminus co-operate to enhance cell migration in cancer. This hypothesis highlights the relevance of Epsin as a cancer-specific, anti-metastatic target. The developmental disease known as LS is caused by the loss of Ocrl1 function; however the disease mechanism has not been established. Our lab discovered that patient’s cells show a dramatic defect in cell migration/ spreading and in the assembly of the sensory organelle known as the primary cilia. We and others also described trafficking defects due to the loss of Ocrl1. In addition, our investigations suggested that RhoGTPase signaling is affected in LS patient cells. Therefore we hypothesize that vesicle trafficking defects and RhoGTPase signaling imbalance underlie the manifestations of this disease. We proposed that Rho modulating drugs can rescue the defects seen in LS patient cells. We anticipate that these investigations will help resolve the mechanism underlying LS, while establishing the basis of drug screens for identifying drugs against LS.
Aguilar, Purdue University.
Off-Campus Purdue Users:
To access this dissertation, please log in to our