Dynll1-PI31 Facilitated Proteasome-Mediated Degradation as a New Therapeutic Target for Interferon 2 (INF2)-Related FSGS: FR-OR106

Jillian Williquett; Hua Sun

doi:10.1681/ASN.20233411S158d

Background: Mutations in Inverted formin 2 (INF2) gene leads to treatment lacking, autosomal dominant Focal Segmental Glomerulosclerosis (FSGS). We found the R218Q mutation in INF2 disrupts the INF2-Dynll1 interaction, leading to dysregulation of dynein-mediated trafficking and degradation of nephrin in in vitro and in vivo models of INF2-mediated podocytopathy. Our previous study found Dynll1 facilitates lysosomal degradation of nephrin via adaptor Histone deacetylase 6 (HDAC6). Here, we identified Proteasomal Inhibitor of 31kD (PI31) as a new adaptor protein which mediates dynein-driven proteosome-mediated degradation. We hypothesized that the INF2-R218Q disinhibits dynein-mediated trafficking of nephrin to the proteasome for degradation via enhanced Dynll1-Pi31 interaction and treatment with Bortezomib (a proteasome protease inhibitor), could become a therapeutic target for INF2-related FSGS. Methods: Proteasome-mediated degradation of nephrin was studied in immortalized podocytes harboring INF2 R218Q mutation, with or without siRNA silencing of Dynll1 or PI31. Puromycin aminonucleoside nephropathy (PAN) was established in INF2 R218Q knockin (KI) mice and effects of Bortezomib versus normal saline control among the different genotypes were evaluated by quantifying severity of proteinuria and podocytopathy. Results: Increased Dynll1-PI31 interaction was shown in R218Q KI podocytes, correlated with the R218Q disrupted Dynll1-INF2 interaction. The nephrin protein in R218Q KI cells could be stabilized by 1) dynein inhibitor Ciliobrevin D and by Bortezomib, suggesting an enhanced dynein-mediated degradation of nephrin via proteasome; or by 2) siRNA mediated knockdown of either Dynll1 or PI31, suggesting a critical role for Dynll1-PI31 interaction in nephrin depletion caused by INF2-R218Q. The Bortezomib treatment rescued the PAN of the INF2-R218Q KI mice by attenuating the dynein-facilitated degradation of nephrin via proteasome and preserving the surface trafficking of nephrin that is needed to maintain the slit diaphragm. Conclusions: The R218Q mutation disrupts the Dynll1-INF2 interaction and facilitates dynein-mediated trafficking of nephrin to the proteasome via an increased Dynll1-PI31 interaction. Enhanced dynein facilitated proteasome-mediated degradation of nephrin represents new therapeutic target for INF2-related FSGS.

Dynll1-PI31 Facilitated Proteasome-Mediated Degradation as a New Therapeutic Target for Interferon 2 (INF2)-Related FSGS: FR-OR106

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