Biology subjects

Marin, L.

Publications and source records attributed to Marin, L..

3 recordsLinked to original sources

bioRxiv2026

PKA/CIP4 SIGNALING REGULATES CIP4 RELOCATION IN ACTIVATED NATURAL KILLER CELLS

Natural killer (NK) cells are cytotoxic lymphocytes of the innate immune system that eliminate virus-infected and transformed cells through the formation of a specialized immune synapse. Effective target cell killing requires coordinated plasma membrane remodeling and dynamic reorganization of the actin and microtubule cytoskeletons, enabling centrosome polarization and directed secretion of lytic granules. The scaffold protein CIP4 has emerged as an important regulator of cytoskeletal coordination in NK cells, yet how its subcellular localization is controlled during NK cell activation is unknown. CIP4 contains a unique protein kinase A (PKA) phosphorylation site (threonine 225, T225) within its F-BAR domain, a domain that mediates interactions with microtubules and the plasma membrane. We hypothesized that localized PKA signaling controls CIP4 redistribution during immune synapse assembly. To test this hypothesis, we analyzed CIP4 localization and phosphorylation in NK cells engaged with sensitive target cells using biochemical and imaging approaches. We show that NK-target cell interaction enhances PKA activity and promotes phosphorylation of CIP4, coinciding with its delocalization from microtubules and accumulation at the immune synapse. Importantly, this relocalization process requires the PKA-anchoring protein AKAP350, which positions PKA and CIP4 within the same protein complex, thereby facilitating CIP4 phosphorylation. Consistently, pharmacological inhibition of PKA prevented CIP4 delocalization from microtubules and reduced its accumulation at the immune synapse. The non-phosphorylatable CIP4 mutant T225A displayed increased association with microtubules compared with a phosphomimetic mutant, identifying phosphorylation at T225 as a key determinant of CIP4 spatial regulation. Together, these findings identify a signaling mechanism that links compartmentalized PKA activity to the spatial control of CIP4 during immune synapse formation, providing new insight into the molecular mechanisms governing immune synapse maturation.

immunology↗

bioRxiv2025

Identification of chaperone-independent outer membrane proteins and MtrA-assisted MtrB folding in Shewanella oneidensis

Extracellular electron transfer is a respiratory process conducted by a number of microorganisms in order to access insoluble or membrane impermeable electron acceptors or donors. The process has wide implication for the biogeochemistry of our planet and offers many opportunities for biotechnological applications. Outer membrane spanning electron transfer is conducted by the model organism Shewanella oneidensis MR-1 by a stable trimeric protein complex. The electron conduit consists of two c-type cytochromes on either site of the outer membrane and a {beta}-barrel protein in the middle that seems to facilitate interaction of the two heme containing proteins. This study reveals that the periplasmic c-type cytochrome MtrA is not only part of the electron conduit, but also assists in the periplasmic transport of the unfolded outer membrane protein MtrB, a function that was so far believed to be conducted for all outer membrane {beta}-barrel proteins by one of the canonical chaperones SurA, Skp or DegP. However, three more {beta}-barrel proteins were identified that are independent of the canonical chaperones as well but still rely on the BAM complex in the outer membrane, suggesting that many more solutions for periplasmic transfer of {beta}-barrel protein towards the outer membrane exist in Gram-negative microorganisms.

microbiology↗

bioRxiv2025

PP6 phosphatase and Elongator contribute to kinesin 5-dependent spindle assembly by controlling microtubule regulator levels

Eukaryotic chromosome segregation relies on the assembly of a bipolar machinery based on microtubules (MTs), named the mitotic spindle. Formation of the mitotic spindle follows a force balance mechanism that ensures the proper capture and separation of sister chromatids. Many proteins have been involved in the establishment of this force balance, although kinesin 5 is well recognized as the major outward pushing force generator, since its inactivation results in monopolar, non-functional spindles. In order to find additional players in the force balance mechanism, we have performed a suppressor screen using a conditional allele of the fission yeast kinesin 5 ortholog Cut7. This screen identified that the lack of the PP6 phosphatase partially suppresses cut7 phenotypes, at least by defective translation of MT regulators, impacting on the force balance mechanism. Additionally, our data show that the Elongator complex, a target regulated by PP6 involved in tRNA modification, also ensures the force balance, albeit to a lesser extent. Importantly, this complex has been recently involved in direct MT polymerization in metazoans, a role probably not shared by its fission yeast counterpart. AUTHOR SUMMARYThe mitotic spindle is a cellular machine made of microtubules, which become arranged in a bipolar manner to capture and segregate chromosomes into the daughter cells during cell division. Spindle bipolarization relies on a force balance mechanism established by the function of many proteins, among which, the essential kinesin 5 is the major outward force generator. To discover novel proteins involved in the force balance, we have screened for suppressors of the kinesin 5 ortholog of fission yeast Cut7. Among the hits of the screen, we found that the lack of PP6 phosphatase components allow cut7 mutants form a bipolar spindle. Our results show that this suppression is, as least in part, mediated by the inactivation of Elongator, a complex that modifies tRNAs to facilitate the translation of specific mRNAs. Our results show that PP6 and Elongator participate in the efficient production of microtubule regulators that contribute to the proper generation of the force balance for spindle assembly.

cell biology↗