Dynamin-mediated Nephrin phosphorylation regulates glucose-stimulated insulin release in pancreatic beta cells.
We have previously demonstrated a role for Nephrin in glucose stimulated insulin release (GSIR). We now hypothesize that Nephrin phosphorylation is required for GSIR and that Dynamin influences Nephrin phosphorylation and function. MIN6-C3 Nephrin-deficient pancreatic beta cells and human islets were transfected with WT-Nephrin or with a mutant Nephrin in which the tyrosine residues responsible for SH2 domain binding were substituted with phenylalanine (3YF-Nephrin). GSIR and live images of Nephrin and vesicle trafficking were studied. Immunoprecipitation experiments and overexpression of WT-Dynamin or dominant negative Dynamin mutant (K44A-Dynamin) in WT-Nephrin, 3YF-Nephrin, or Nephrin siRNA-transfected cells were utilized to study Nephrin-Dynamin interaction. In contrast to WT-Nephrin or to single tyrosine mutants, 3YF-Nephrin did not positively affect GSIR and led to impaired cell-cell contacts and vesicle trafficking. K44A-Dynamin prevented the effect of Nephrin on GSIR in the absence of protein-protein interaction between Nephrin and Dynamin. Nephrin gene silencing abolished the positive effects of WT-Dynamin on GSIR. The effects of protamine sulfate and vanadate on Nephrin phosphorylation and GSIR were studied in MIN6 cells and human islets. WT-Nephrin phosphorylation after glucose occurred at Tyr-1176/1193 and resulted in improved GSIR. On the contrary, protamine sulfate-induced phosphorylation at Tyr-1176/1193/1217 was associated with Nephrin degradation and impaired GSIR. Vanadate, which prevented Nephrin dephosphorylation after glucose stimulation, improved GSIR in human islets and MIN6 cells. In conclusion, Dynamin-dependent Nephrin phosphorylation occurs in response to glucose and is necessary for Nephrin-mediated augmentation of GSIR. Pharmacological modulation of Nephrin phosphorylation may thus facilitate pancreatic beta cell function.
Diabetes Research Institute, University of Miami L. Miller School of Medicine, Miami, Florida 33136, USA.
Jongmin
J
Jeon
Ingo
I
Leibiger
Tilo
T
Moede
Britta
B
Walter
Christian
C
Faul
Dony
D
Maiguel
Rodrigo
R
Villarreal
Johanna
J
Guzman
Per-Olof
PO
Berggren
Peter
P
Mundel
Camillo
C
Ricordi
Sandra
S
Merscher-Gomez
Alessia
A
Fornoni
D019943:Amino Acid Substitution; D034281:Dynamins / Q000235:genetics / Q000378:metabolism*; D020868:Gene Silencing; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D059748:Proteolysis; D013549:Sweetening Agents / Q000378:metabolism / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
D007328:Insulin; D008565:Membrane Proteins; D013549:Sweetening Agents; C113267:nephrin; D014638:Vanadates; D034281:Dynamins; D005947:Glucose