Lipid Transfer Proteins and Membrane Contact Sites in Human Cancer.

Lipid-transfer proteins (LTPs) were initially discovered as cytosolic factors that facilitate lipid transport between membrane bilayers in vitro. Since then, many LTPs have been isolated from bacteria, plants, yeast, and mammals, and extensively studied in cell-free systems and intact cells. A major advance in the LTP field was associated with the discovery of intracellular membrane contact sites (MCSs), small cytosolic gaps between the endoplasmic reticulum (ER) and other cellular membranes, which accelerate lipid transfer by LTPs. As LTPs modulate the distribution of lipids within cellular membranes, and many lipid species function as second messengers in key signaling pathways that control cell survival, proliferation, and migration, LTPs have been implicated in cancer-associated signal transduction cascades. Increasing evidence suggests that LTPs play an important role in cancer progression and metastasis. This review describes how different LTPs as well as MCSs can contribute to cell transformation and malignant phenotype, and discusses how "aberrant" MCSs are associated with tumorigenesis in human

The COG complex interacts directly with Syntaxin 6 and positively regulates endosome-to-TGN retrograde transport

The conserved oligomeric Golgi (COG) complex interacts with the t-SNARE Syntaxin 6 and promotes endosome-to-TGN retrograde trafficking

Nir2, a Human Homolog of Drosophila melanogaster Retinal Degeneration B Protein, Is Essential for Cytokinesis

Cytokinesis, the final stage of eukaryotic cell division, ensures the production of two daughter cells. It requires fine coordination between the plasma membrane and cytoskeletal networks, and it is known to be regulated by several intracellular proteins, including the small GTPase Rho and its effectors. In this study we provide evidence that the protein Nir2 is essential for cytokinesis. Microinjection of anti-Nir2 antibodies into interphase cells blocks cytokinesis, as it results in the production of multinucleate cells. Immunolocalization studies revealed that Nir2 is mainly localized in the Golgi apparatus in interphase cells, but it is recruited to the cleavage furrow and the midbody during cytokinesis. Nir2 colocalizes with the small GTPase RhoA in the cleavage furrow and the midbody, and it associates with RhoA in mitotic cells. Its N-terminal region, which contains a phosphatidylinositol transfer domain and a novel Rho-inhibitory domain (Rid), is required for normal cytokinesis, as overexpression of an N-terminal-truncated mutant blocks cytokinesis completion. Time-lapse videomicroscopy revealed that this mutant normally initiates cytokinesis but fails to complete it, due to cleavage furrow regression, while Rid markedly affects cytokinesis due to abnormal contractility. Rid-expressing cells exhibit aberrant ingression and ectopic cleavage sites; the cells fail to segregate into daughter cells and they form a long unseparated bridge-like cytoplasmic structure. These results provide new insight into the cellular functions of Nir2 and introduce it as a novel regulator of cytokinesis

The AXL-PYK2-PKCα axis as a nexus of stemness circuits in TNBC

International audienceCancer stem cells (CSCs) are implicated in tumor initiation, metastasis and drug resistance, and considered as attractive targets for cancer therapy. Here we identified a clinically relevant signaling nexus mediated by AXL receptor, PYK2 and PKCα and show its impact on stemness in TNBC. AXL, PYK2, and PKCα expression correlates with stemness signature in basal-like breast cancer patients, and their depletion in multiple mesenchymal TNBC cell lines markedly reduced the number of mammosphere-forming cells and cells harboring CSCs characteristic markers. Knockdown of PYK2 reduced the levels of AXL, PKCα, FRA1, and PYK2 proteins, and similar trend was obtained upon PKCα depletion. PYK2 depletion decreased AXL transcription through feedback loops mediated by FRA1 and TAZ, whereas PKCα inhibition induced redistribution of AXL to endosomal/lysosomal compartment and enhanced its degradation. PYK2 and PKCα cooperate at a convergence point of multiple stemness-inducing pathways to regulate AXL levels and concomitantly the levels/activation of STAT3, TAZ, FRA1, and SMAD3 as well as the pluripotent transcription factors Nanog and Oct4. Induction of stemness in TNBC sensitized cells to PYK2 and PKCα inhibition suggesting that targeting the AXL-PYK2-PKCα circuit could be an efficient strategy to eliminate CSCs in TNBC

Tethering the assembly of SNARE complexes

Binational Science Foundation (BSF) [2011404]The fusion of transport vesicles with their target membranes is fundamental for intracellular membrane trafficking and diverse physiological processes and is driven by the assembly of functional soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes. Prior to fusion, transport vesicles are physically linked to their target membranes by various tethering factors. Recent studies suggest that tethering factors also positively regulate the assembly of functional SNARE complexes, thereby coupling tethering with fusion events. This coupling is mediated, at least in part, by direct physical interactions between tethering factors, SNAREs, and Sec1/Munc18 (SM) proteins. In this review we summarize recent progress in understanding the roles of tethering factors in the assembly of specific and functional SNARE complexes driving membrane-fusion events

Nir2, a Novel Regulator of Cell Morphogenesis

Cell morphogenesis requires dynamic reorganization of the actin cytoskeleton, a process that is tightly regulated by the Rho family of small GTPases. These GTPases act as molecular switches by shuttling between their inactive GDP-bound and active GTP-bound forms. Here we show that Nir2, a novel protein related to Drosophila retinal degeneration B (RdgB), markedly affects cell morphology through a novel Rho-inhibitory domain (Rid) which resides in its N-terminal region. Rid exhibits sequence homology with the Rho-binding site of formin-homology (FH) proteins and leads to an apparent loss of F-actin staining when ectopically expressed in mammalian cells. We also show that Rid inhibits Rho-mediated stress fiber formation and lysophosphatidic acid-induced RhoA activation. Biochemical studies demonstrated that Nir2, via Rid, preferentially binds to the inactive GDP-bound form of the small GTPase Rho. Microinjection of antibodies against Nir2 into neuronal cells markedly attenuates neurite extension, whereas overexpression of Nir2 in these cells attenuates Rho-mediated neurite retraction. These results implicate Nir2 as a novel regulator of the small GTPase Rho in actin cytoskeleton reorganization and cell morphogenesis