synneabj

• Bjørnestad, Synne Arstad; Solbakken, Monica Hongrø; Krokene, Pia; Thiede, Bernd; Hylland, Ketil & Jakobsen, Kjetill Sigurd [Vis alle 9 forfattere av denne artikkelen] (2024). The Atlantic Cod MHC I compartment has the properties needed for cross-presentation in the absence of MHC II. Scientific Reports. 14(1). doi: 10.1038/s41598-024-76225-z. Fulltekst i vitenarkiv Vis sammendrag

  Atlantic cod has a peculiar immune system, characterized by the loss of Major Histocompatibility Complex (MHC) class II pathway, and an extreme expansion of the MHC class I gene repertoire. This has led to the hypothesis that some of the MHC I variants have replaced MHC II by presenting exogenous-peptides in a process similar to cross-presentation. In mammals, MHC I loads endogenous antigens in the endoplasmic reticulum, but we recently found that different Atlantic cod MHC I gene variants traffic to endolysosomes. There, they colocalize with Tapasin and other components of the peptide-loading complex, indicating a plausible peptide-loading system outside the endoplasmic reticulum. In this study, we further characterize the identity of the Atlantic cod MHC I compartment (cMIC). We found that, similarly to mammalian MHC II compartment, cMIC contains late endosomal markers such as Rab7, LAMP1 and CD63. Furthermore, we identified Hsp90b1 (also known as grp94) and LRP1 (also known as CD91) as interactors of MHC I by mass spectrometry. As these two proteins are involved in cross-presentation in mammals, this further suggests that Atlantic cod MHC I might use a similar mechanism to present exogenous peptides, thus, compensating for the absence of MHC II.

• Bjørnestad, Synne Arstad; Solbakken, Monica Hongrø; Jakobsen, Kjetill Sigurd; Jentoft, Sissel; Bakke, Oddmund & Progida, Cinzia (2023). Atlantic cod (Gadus morhua) MHC I localizes to endolysosomal compartments independently of cytosolic sorting signals. Frontiers in Cell and Developmental Biology. 11, s. 1–15. doi: 10.3389/fcell.2023.1050323. Fulltekst i vitenarkiv Vis sammendrag

  Major histocompatibility complex (MHC) class I and II are crucial for the adaptive immune system because they are involved in peptide presentation to T cells. Until recently, it was believed that MHC genes and their associated immune components had been conserved since their evolutionary emergence in jawed fish. However, sequencing of the Atlantic cod ( Gadus morhua ) genome revealed a loss of MHC class II genes, and an extreme expansion of MHC class I genes. These findings lead to the hypothesis that a loss of the MHC class II pathway coincided with a more versatile use of MHC class I, but so far there is no direct experimental evidence in support of this. To gain a deeper understanding of the function of the expanded MHC class I, we selected five MHC class I gene variants representing five of the six clades identified in previous studies and investigated their intracellular localization in human and Atlantic cod larval cells. Intriguingly, we uncovered that all selected MHC class I variants localize to endolysosomal compartments in Atlantic cod cells. Additionally, by introducing point mutations or deletions in the cytosolic tail, we found that hypothetical sorting signals in the MHC class I cytosolic tail do not influence MHC class I trafficking. Moreover, we demonstrated that in Atlantic cod, tapasin and MHC class I colocalize on endolysosomes suggesting that peptide-loading assistance and stabilization of MHC class I occurs outside the endoplasmic reticulum. Altogether, our results demonstrate that MHC class I from Atlantic cod is sorted to the endolysosomal system, which may indicate that it interacts with exogenous peptides for potential cross presentation.

• Bjørnestad, Synne Arstad; Guadagno, Noemi Antonella; Kjos, Ingrid & Progida, Cinzia (2022). Rab33b-exocyst interaction mediates localized secretion for focal adhesion turnover and cell migration. iScience. 25(5). doi: 10.1016/j.isci.2022.104250. Fulltekst i vitenarkiv Vis sammendrag

  Rab proteins are well known regulators of intracellular trafficking; however, more and more studies point to their function also in other cellular processes, including cell migration. In this work, we have performed an siRNA screen to identify Rab proteins that influence cell migration. The screen revealed Rab33b as the strongest candidate that affected cell motility. Rab33b has been previously reported to localize at the Golgi apparatus to regulate Golgi-to-ER retrograde trafficking and Golgi homeostasis. We revealed that Rab33b also mediates post-Golgi transport to the plasma membrane. We further identified Exoc6, a subunit of the exocyst complex, as an interactor of Rab33b. Moreover, our data indicate that Rab33b regulates focal adhesion dynamics by modulating the delivery of cargo such as integrins to focal adhesions. Altogether, our results demonstrate a role for Rab33b in cell migration by regulating the delivery of integrins to focal adhesions through the interaction with Exoc6.

• Guadagno, Noemi Antonella; Margiotta, Azzurra; Bjørnestad, Synne Arstad; Haugen, Linda Hofstad; Kjos, Ingrid & Xiaochun, Xu [Vis alle 10 forfattere av denne artikkelen] (2020). Rab18 regulates focal adhesion dynamics by interacting with kinectin-1 at the endoplasmic reticulum. Journal of Cell Biology. ISSN 0021-9525. 219(7), s. 1–23. doi: 10.1083/JCB.201809020. Fulltekst i vitenarkiv Vis sammendrag

  The members of the Rab family of small GTPases are molecular switches that regulate distinct steps in different membrane traffic pathways. In addition to this canonical function, Rabs can play a role in other processes, such as cell adhesion and motility. Here, we reveal the role of the small GTPase Rab18 as a positive regulator of directional migration in chemotaxis, and the underlying mechanism. We show that knockdown of Rab18 reduces the size of focal adhesions (FAs) and influences their dynamics. Furthermore, we found that Rab18, by directly interacting with the endoplasmic reticulum (ER)-resident protein kinectin-1, controls the anterograde kinesin-1–dependent transport of the ER required for the maturation of nascent FAs and protrusion orientation toward a chemoattractant. Altogether, our data support a model in which Rab18 regulates kinectin-1 transport toward the cell surface to form ER–FA contacts, thus promoting FA growth and cell migration during chemotaxis

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