Nuclear translocation of the 4-pass transmembrane protein Tspan8.
Ontology highlight
ABSTRACT:
SUBMITTER: Huang Y
PROVIDER: S-EPMC8563794 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:TSPAN family of proteins are generally considered to assemble as multimeric complexes on the plasma membrane. Our previous work uncovered that TSPAN8 can translocate into the nucleus as a membrane-free form, a process that requires TSPAN8 palmitoylation and association with cholesterol to promote its extraction from the plasma membrane and subsequent binding with 14-3-3θ and importin-β. However, what upstream signal(s) regulate(s) the nuclear translocation of TSPAN8, the potential function of TSPAN8 in the nucleus, and the underlying molecular mechanisms all remain unclear. Here, we demonstrate that, epidermal growth factor receptor (EGFR) signaling induces TSPAN8 nuclear translocation by activating the kinase AKT, which in turn directly phosphorylates TSPAN8 at Ser129, an event essential for its binding with 14-3-3θ and importin ß1. In the nucleus, phosphorylated TSPAN8 interacts with STAT3 to enhance its chromatin occupancy and therefore regulates transcription of downstream cancer-promoting genes, such as MYC, BCL2, MMP9, etc. The EGFR-AKT-TSPAN8-STAT3 axis was found to be hyperactivated in multiple human cancers, and associated with aggressive phenotype and dismal prognosis. We further developed a humanized monoclonal antibody hT8Ab4 that specifically recognizes the large extracellular loop of TSPAN8 (TSPAN8-LEL), thus being able to block the extraction of TSPAN8 from the plasma membrane and consequently its nuclear localization. Importantly, both in vitro and in vivo studies demonstrated an antitumor effect of hT8Ab4. Collectively, we discovered an unconventional function of TSPAN8 and dissected the underlying molecular mechanisms, which not only showcase a new layer of biological complexity of traditional membrane proteins, but also shed light on TSPAN8 as a novel therapeutic target for refractory cancers.
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Project description:TM4SF20 (transmembrane 4 L6 family 20) is a polytopic membrane protein that inhibits proteolytic processing of CREB3L1 (cAMP response element-binding protein 3-like 1), a membrane-bound transcription factor that blocks cell division and activates collagen synthesis. Here we report that ceramide stimulates CREB3L1 cleavage by inverting the orientation of TM4SF20 in membranes. In the absence of ceramide, the N terminus of the first transmembrane helix of TM4SF20 is inserted into the endoplasmic reticulum (ER) lumen. This translocation requires TRAM2 (translocating chain-associated membrane protein 2), a membrane protein containing a putative ceramide-interacting domain. In the presence of ceramide, the N terminus of the first transmembrane domain of TM4SF20 is exposed to cytosol. Consequently, the membrane topology of TM4SF20 is inverted, and this form of TM4SF20 stimulates CREB3L1 cleavage. In the presence of ceramide, translocation of TM4SF20 is TRAM2-independent. We designate this mechanism-causing regulated inversion of the membrane topology as "regulated alternative translocation."
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Project description:Single-pass transmembrane receptors (SPTMRs) represent a diverse group of integral membrane proteins that are involved in many essential cellular processes, including signal transduction, cell adhesion, and transmembrane transport of materials. Dysregulation of the SPTMRs is linked with many human diseases. Despite extensive efforts in past decades, the mechanisms of action of the SPTMRs remain incompletely understood. One major hurdle is the lack of structures of the full-length SPTMRs in different functional states. Such structural information is difficult to obtain by traditional structural biology methods such as X-ray crystallography and nuclear magnetic resonance (NMR). The recent rapid development of single-particle cryo-electron microscopy (cryo-EM) has led to an exponential surge in the number of high-resolution structures of integral membrane proteins, including SPTMRs. Cryo-EM structures of SPTMRs solved in the past few years have tremendously improved our understanding of how SPTMRs function. In this review, we will highlight these progresses in the structural studies of SPTMRs by single-particle cryo-EM, analyze important structural details of each protein involved, and discuss their implications on the underlying mechanisms. Finally, we also briefly discuss remaining challenges and exciting opportunities in the field.
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Project description:Major depression disorder is one of the most common psychiatric diseases. Recent evidence supports that environmental stress affects gene expression and promotes the pathological process of depression through epigenetic mechanisms. Three ten-eleven translocation (Tet) enzymes are epigenetic regulators of gene expression that promote 5-hydroxymethylcytosine (5hmC) modification of genes. Here, we show that the loss of Tet2 can induce depression-like phenotypes in mice. Paradoxically, using the paradigms of chronic stress, such as chronic mild stress and chronic social defeat stress, we found that depressive behaviors were associated with increased Tet2 expression but decreased global 5hmC level in hippocampus. We examined the genome-wide 5hmC profile in the hippocampus of Tet2 knockout mice and identified 651 dynamically hydroxymethylated regions, some of which overlapped with known depression-associated loci. We further showed that chronic stress could induce the abnormal nuclear translocation of Tet2 protein from cytosol. Through Tet2 immunoprecipitation and mass spectrum analyses, we identified a cellular trafficking protein, Abelson helper integration site-1 (Ahi1), which could interact with Tet2 protein. Ahi1 knockout or knockdown caused the accumulation of Tet2 in cytosol. The reduction of Ahi1 protein under chronic stress explained the abnormal Ahi1-dependent nuclear translocation of Tet2. These findings together provide the evidence for a critical role of modulating Tet2 nuclear translocation in regulating stress response.
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