Identification of Phosphotyrosine Binding Domain-Containing Proteins as Novel Downstream Targets of the EphA8 Signaling Function▿ †

Eph receptors and ephrins have been implicated in a variety of cellular processes, including morphology and motility, because of their ability to modulate intricate signaling networks. Here we show that the phosphotyrosine binding (PTB) domain-containing proteins AIDA-1b and Odin are tightly associated with the EphA8 receptor in response to ligand stimulation. Both AIDA-1b and Odin belong to the ankyrin repeat and sterile alpha motif domain-containing (Anks) protein family. The PTB domain of Anks family proteins is crucial for their association with the juxtamembrane domain of EphA8, whereas EphA8 tyrosine kinase activity is not required for this protein-protein interaction. In addition, we found that Odin is a more physiologically relevant partner of EphA8 in mammalian cells. Interestingly, overexpression of the Odin PTB domain alone attenuated EphA8-mediated inhibition of cell migration in HEK293 cells, suggesting that it acts as a dominant-negative mutant of the endogenous Odin protein. More importantly, small interfering RNA-mediated Odin silencing significantly diminished ephrinA5-induced EphA8 signaling effects, which inhibit cell migration in HEK293 cells and retract growing neurites of Neuro2a cells. Taken together, our findings support a possible function for Anks family proteins as scaffolding proteins of the EphA8 signaling pathway

Anks1a regulates COPII-mediated anterograde transport of receptor tyrosine kinases critical for tumorigenesis

AbstractErbB2 signalling, which is amplified by EphA2 binding, is an important therapeutic target for breast cancer. Despite the importance of the EphA2/ErbB2 complex in promoting breast tumorigenesis, the mechanism by which these receptor tyrosine kinases (RTKs) are exported from the endoplasmic reticulum (ER) remains poorly understood. Here we report that the PTB adaptor Anks1a is specifically localized to the ER on its own serine phosphorylation. Once there, Anks1a acts as an important regulator of COPII-mediated EphA2 ER export. The Anks1a ankyrin repeat domain binds EphA2 and causes it to accumulate at sites of ER exit. Simultaneously, the Anks1a PTB domain binds Sec23. This induces internalization of EphA2 via COPII vesicles, while Anks1a remains behind on the ER membrane. EphA2 also binds ErbB2 in the ER and seems to load ErbB2 into growing COPII carriers. Together, our study reveals a novel mechanism that regulates the loading of RTKs into COPII vesicles.</jats:p

Truncated suPAR simultaneously causes kidney disease and autoimmune diabetes mellitus

AbstractSoluble urokinase-type plasminogen activator receptor (suPAR) is a risk factor for kidney diseases. Here we report the presence of C-terminal suPAR fragment, D2D3, in patients with diabetic nephropathy. D2D3-positive human sera inhibited glucose-stimulated insulin release in human islets and were associated with patients requiring insulin therapy. D2D3 transgenic mice presented kidney disease and diabetes marked by decreased levels of insulin and C-peptide, impaired glucose-stimulated insulin secretion, decreased pancreatic β-cell mass, and high fasting glucose. D2D3 fragment dysregulated glucose-induced cytoskeletal dynamics, impaired maturation and trafficking of insulin granules, and inhibited bioenergetics of β-cells in culture. An anti-uPAR antibody restored β-cell function in D2D3 transgenic mice. We show that the D2D3 fragment injures the kidney and pancreas, offering a unique dual therapeutic approach for kidney diseases and insulin-dependent diabetes.SummaryProteolytic suPAR fragment, D2D3, simultaneously injures two organs, the kidney and pancreas, thus causing a dual organ disease.</jats:sec