Co-transplantation of MSCs may lead to improved islet function and survival in the early post-transplantation period in humans receiving islet transplantation.

ADP-ribosylation factor (ARF)-related protein 1 (ARFRP1) is a GTPase

ADP-ribosylation factor related protein 1 (ARFRP1) is a member of the ARF-family of GTPases which operate as molecular switches in the regulation of intracellular protein traffic. Deletion of the mouse Arfrp1 gene leads to embryonic lethality during early gastrulation, suggesting that ARFRP1 is required for cell adhesion-related processes. Here we show that ARFRP1 specifically controls targeting of ARL1 and its effector Golgin-245 to the trans-Golgi. GTP-bound ARFRP1 (ARFRP1-Q79L mutant) is associated with Golgi membranes and co-localized with the GTPase ARL1. In contrast, the guanine nucleotide exchange defective ARFRP1 mutant (ARFRP1-T31N) clusters within the cytosol. ARFRP1-T31N or depletion of endogenous ARFRP1 by RNA interference disrupts the Golgi association of ARL1 and of the GRIP-domain protein Golgin-245 and alters the distribution of a trans-Golgi network marker, syntaxin 6. In contrast, the targeting of two other Golgi-associated proteins, GM130 and giantin, was unaffected. Furthermore, in Arfrp1-/ - embryos ARL1 dislocated from Golgi membranes whereas it was associated with intracellular membranes in wild-type embryos. These data suggest that lethality of Arfrp1 knockout embryos is due to a specific disruption of protein targeting, e.g., of ARL1 and Golgin-245, to the Golgi.

ADP-ribosylation factor-related protein 1 (ARFRP1) plays a specific role in Golgi function controlling recruitment of GRIP domain proteins and ARL1 to the trans-Golgi. Deletion of the mouse Arfrp1 gene causes embryonic lethality during early gastrulation, because epiblast cells detach from the ectodermal cell layer and do not differentiate to mesodermal tissue. Here we show that in Arfrp1 ؊/؊ embryos E-cadherin is mistargeted to intracellular compartments, whereas in control embryos it is present at the cell surface of trophectodermal and ectodermal cells. In enterocytes of intestine-specific Arfrp1 null mutants (Arfrp1), E-cadherin is associated with intracellular membranes, partially colocalizing with the cis-Golgi marker GM130 or with punctae close to the cell surface. In contrast, in control enterocytes E-cadherin is exclusively located in the lateral membranes. In addition, ARL1 is dislocated from Golgi membranes to the cytosol of Arfrp1 vil؊/؊ enterocytes. Depletion of endogenous ARFRP1 by RNA interference leads to a dislocation of E-cadherin from the cell surface in HeLa cells and to a reduced cell aggregation in Ltk ؊ Ecad cells. ARFRP1 was coimmunoprecipitated in a complex with E-cadherin, ␣-catenin, ␤-catenin, ␥-catenin, and p120 ctn from lysates of MadinDarby canine kidney cells stably expressing myc-ARFRP1. These data indicate that knock-out of Arfrp1 disrupts the trafficking of E-cadherin through the Golgi and suggest an essential role of the GTPase in trans-Golgi network function.

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