MVB12B

MVB12B is the fourth subunit class of human ESCRT-I, associating with the core TSG101-VPS37 binary complex through conserved C-terminal sequence elements to form a complex containing one copy of each of the four subunit types (PMID:18005716). Its MABP domain adopts a β-prism fold with a hydrophobic membrane-anchoring loop and an electropositive patch that binds acidic phosphoinositide-containing membranes in a charge-density-dependent, non-stereoselective manner, allowing ESCRT-I to act as a coincidence detector for acidic phospholipids and protein ligands (PMID:22232651). Functionally, MVB12B is dispensable for canonical ubiquitin-dependent cargo sorting at the MVB, distinguishing it from UBAP1 and indicating specialization within the ESCRT-I subunit family (PMID:24284069). Instead, MVB12B is dedicated to unconventional and stress- or infection-induced trafficking routes: TBK1 phosphorylates MVB12B downstream of STING during intracellular bacterial infection, and this modification is essential for sorting bacterial DNA into extracellular vesicles that activate cGAS-STING signaling in bystander cells and suppress T-cell responses (PMID:30804548), and MVB12B is required for ER-stress-stimulated unconventional secretion of CFTRΔF508 (PMID:29969945). Its activity is further regulated by EGF-induced Tyr241/Tyr243 phosphorylation and Lys264/Lys290 ubiquitination that drive its instability and aggregation (PMID:20654576).

1. 2007 High

   Established that MVB12B is a bona fide structural component of ESCRT-I rather than a peripheral associate, defining the four-subunit architecture of the human complex and a role in viral budding.

   Evidence Co-IP, hydrodynamic reconstitution, and HIV-1 budding/morphology assays with siRNA depletion and overexpression

   PMID:18005716

   Open questions at the time

   • Did not define how MVB12B contributes mechanistically to membrane budding beyond complex incorporation
   • No structural basis for TSG101-VPS37 binding resolved
2. 2010 Medium

   Identified post-translational control of MVB12B by EGF-driven tyrosine phosphorylation and ubiquitination, linking receptor signaling to ESCRT-I subunit stability.

   Evidence Site-directed mutagenesis, Co-IP, EGF stimulation and proteasome inhibition in COS-7 cells

   PMID:20654576

   Open questions at the time

   • Kinase responsible for Tyr241/Tyr243 phosphorylation not identified
   • Functional consequence of aggregation for cargo handling not resolved
3. 2012 High

   Resolved the structural basis for MVB12B membrane engagement, showing the MABP domain is a β-prism that reads acidic lipid charge density and supports a coincidence-detection model for ESCRT-I.

   Evidence 1.3-Å X-ray crystal structure, in vitro liposome binding, and live-cell localization

   PMID:22232651

   Open questions at the time

   • Specific physiological membranes engaged in cells not defined
   • How lipid binding is coordinated with protein-ligand recognition not directly tested
4. 2013 Medium

   Demonstrated functional specialization within ESCRT-I by showing MVB12B is dispensable for ubiquitin-dependent MVB cargo sorting, unlike UBAP1.

   Evidence siRNA depletion, Co-IP, and EGF receptor sorting assay

   PMID:24284069

   Open questions at the time

   • The cargoes or pathways that DO require MVB12B were not identified here
   • Whether MVB12B pairs nonselectively with all VPS37 isoforms in cells not fully resolved
5. 2018 Medium

   Placed MVB12B in a non-canonical secretory route, showing it is required for ER-stress-induced unconventional secretion of misfolded CFTR.

   Evidence ESCRT siRNA knockdown screen with CFTRΔF508 surface expression and Cl⁻ channel assays plus overexpression rescue

   PMID:29969945

   Open questions at the time

   • Direct interaction between MVB12B and CFTR not shown
   • Mechanism linking ESCRT-I to the unconventional secretory carrier undefined
6. 2019 High

   Defined a signaling-coupled cargo-sorting function: TBK1 phosphorylation of MVB12B directs bacterial DNA into extracellular vesicles for paracrine innate immune signaling.

   Evidence Phosphoproteomic MS, MVB12B siRNA knockdown, EV isolation, bystander cGAS-STING activation, and T-cell proliferation/apoptosis assays

   PMID:30804548

   Open questions at the time

   • TBK1 phosphosite(s) on MVB12B not mapped here
   • How phosphorylation redirects DNA cargo into the EV pathway mechanistically unresolved
7. 2025 Low

   Suggested a tumor-suppressive cellular phenotype for MVB12B in bladder urothelial carcinoma via overexpression effects on proliferation and migration.

   Evidence Overexpression in BLCA cell lines with proliferation/migration assays and PPI network analysis

   PMID:41510117

   Open questions at the time

   • Single-lab overexpression phenotype without rescue or in vivo validation
   • No mechanistic link between ESCRT-I activity and the anti-proliferative effect
   • Loss-of-function evidence absent

• It remains unknown which physiological cargoes MVB12B selectively routes and how its membrane-binding, phosphorylation, and ubiquitination states are integrated to switch between canonical ESCRT-I and unconventional secretory functions.
• No unified model connecting MABP lipid binding to cargo selection
• Substrate code distinguishing EV-DNA sorting from CFTR secretion not defined