DIP2A

DIP2A is a conserved, multifunctional protein whose adenylate-forming domains regulate diacylglycerol subspecies homeostasis and lipid metabolism, while also serving as a cell-surface receptor for FSTL1 to activate Akt and Smad2/3 signaling independently of TGFβR1 (PMID:20054002, PMID:33246164). In the nucleus, DIP2A partners with the HDAC2-DMAP1 complex to deacetylate H3K9 and repress MGMT transcription, a function antagonized by FSTL1-mediated cytoplasmic sequestration (PMID:30542120). DIP2A maintains dendritic spine morphology by binding cortactin through PXXP motifs and sustaining cortactin acetylation, while its mitochondrial pool supports SOD-mediated antioxidant defense and acetyl-CoA production (PMID:31600191, PMID:33781892). The conserved adenylate-forming domains are essential for redirecting specific diacylglycerol species to triacylglycerol storage to prevent ER stress and, in neurons, for cell-autonomous suppression of ectopic neurite sprouting and axon regeneration in opposition to phospholipid synthesis pathways (PMID:35766356, PMID:30396999).

1. 2010 High

   The identity of the cell-surface receptor mediating FSTL1 signaling was unknown; demonstration that DIP2A directly binds FSTL1 and is required for FSTL1-induced Akt phosphorylation and cytoprotection established DIP2A as a transmembrane receptor activating pro-survival signaling.

   Evidence Co-IP, siRNA knockdown of DIP2A in endothelial cells and cardiomyocytes, membrane fractionation, Biacore binding kinetics

   PMID:20054002 PMID:20860622

   Open questions at the time

   • No structural basis for FSTL1-DIP2A interaction
   • Mechanism by which DIP2A transduces signal to Akt is undefined
   • Whether DIP2A acts as receptor in non-cardiovascular cell types not established
2. 2018 High

   How DIP2A influences gene expression was unclear; showing that DIP2A cooperates with HDAC2-DMAP1 to deacetylate H3K9 at the MGMT promoter, and that FSTL1 blocks this by sequestering DIP2A cytoplasmically, revealed a nuclear co-repressor function modulated by extracellular ligand availability.

   Evidence Co-IP, H3K9Ac ChIP, nuclear fractionation, siRNA/overexpression, xenograft model in glioma cells

   PMID:30542120

   Open questions at the time

   • Genome-wide targets of DIP2A-HDAC2-DMAP1 repression unknown
   • Whether DIP2A directly contacts chromatin or is recruited via DMAP1 not resolved
3. 2018 High

   The neuronal function of DIP2A's conserved adenylate-forming domains was uncharacterized; C. elegans genetics showed that DIP-2 cell-autonomously suppresses ectopic neurite sprouting and axon regeneration through its AFDs but independently of its DMAP1-binding domain, separating its lipid-metabolic and chromatin functions.

   Evidence C. elegans loss-of-function genetics, domain mutagenesis, epistasis with dlk-1 and efa-6, in vivo neuronal imaging

   PMID:30396999

   Open questions at the time

   • Enzymatic substrate of the AFDs in neurons not identified
   • Downstream effectors linking AFD activity to neurite suppression unknown
4. 2018 Medium

   Whether the FSTL1-DIP2A axis functions in immune evasion was unexplored; tumor model experiments showed DIP2A expression in cancer cells is required for FSTL1-induced immunoresistance and metastasis.

   Evidence Mouse tumor models with DIP2A manipulation, immune cell profiling

   PMID:30110636

   Open questions at the time

   • Downstream signaling pathway mediating immune suppression via DIP2A not delineated
   • Whether DIP2A-dependent immune effects are Akt- or Smad-mediated not tested
5. 2019 High

   The synaptic role of DIP2A was unknown; Dip2a knockout mice revealed that DIP2A binds cortactin via PXXP-SH3 interactions to sustain cortactin acetylation, and loss causes thin postsynaptic densities, impaired spine morphogenesis, and reduced synaptic transmission, rescued by acetylation-mimetic cortactin.

   Evidence Dip2a knockout mouse, Co-IP, PXXP domain mutagenesis, electrophysiology, behavioral testing, acetylation assay with rescue

   PMID:31600191

   Open questions at the time

   • Acetyltransferase that modifies cortactin downstream of DIP2A not identified
   • Whether cortactin mechanism is conserved beyond rodents unknown
6. 2019 Medium

   Whether DIP2A possesses intrinsic enzymatic activity was unclear; in vitro assays demonstrated acetyl-CoA synthetase activity, and overexpression increased cellular acetyl-CoA, linking DIP2A to metabolic acetyl-CoA generation at mitochondria.

   Evidence In vitro acetyl-CoA synthetase assay, subcellular fractionation, overexpression in HEK293 cells

   PMID:30672040

   Open questions at the time

   • Kinetic parameters and physiological substrate specificity not defined
   • Contribution relative to canonical ACS enzymes not established
   • Single-lab observation
7. 2020 Medium

   Whether DIP2A signals through pathways beyond Akt was unknown; FSTL1-DIP2A was shown to phosphorylate Smad2/3 independently of TGFβR1, promoting VEGF-A upregulation and cardiac angiogenesis.

   Evidence Phospho-Smad2/3 western blot, TGFβR1 inhibitor dissection, HUVEC tubule assay, AAV-FSTL1 in vivo

   PMID:33246164

   Open questions at the time

   • Mechanism by which DIP2A activates Smad2/3 without TGFβR1 not defined
   • Single lab, limited cell type
8. 2021 Medium

   The mitochondrial role of DIP2A beyond acetyl-CoA synthesis was uncharacterized; Dip2a knockout mice showed impaired SOD activity, elevated ROS, abnormal mitochondrial morphology, and metabolic reliance on lipid oxidation, establishing DIP2A as a regulator of mitochondrial antioxidant defense.

   Evidence Dip2a knockout mouse brain, SOD activity assay, ROS measurement, electron microscopy, metabolic profiling

   PMID:33781892

   Open questions at the time

   • Whether DIP2A directly activates SOD or acts indirectly via acetyl-CoA/lipid metabolism unresolved
   • Single lab, correlation between acetyl-CoA and SOD activity not formally tested
9. 2022 High

   The biochemical function of DIP2's adenylate-forming domains was unresolved; cross-species lipidomics and reconstitution showed DIP2 acts as a DAG-species-selective enzyme redirecting specific diacylglycerols to triacylglycerol storage, preventing toxic DAG accumulation and ER stress, and localizes to mitochondria-vacuole contact sites to modulate membrane fusion.

   Evidence Yeast and Drosophila genetics, lipidomics, in vitro biochemical assay of AFDs, fluorescence microscopy

   PMID:35766356

   Open questions at the time

   • Exact catalytic mechanism of AFD-mediated DAG-to-TAG conversion not fully reconstituted
   • Whether mammalian DIP2A performs identical lipid channeling not directly tested in mammalian systems

• How DIP2A's multiple activities — receptor signaling, chromatin repression, cortactin regulation, acetyl-CoA synthesis, and DAG homeostasis — are coordinated across subcellular compartments remains unresolved, and no structural model of full-length DIP2A exists.
• No high-resolution structure of DIP2A or its domains
• Relative contribution of receptor vs. enzymatic functions in vivo not dissected
• Whether human genetic variants in DIP2A cause a Mendelian disorder not established