CDIP1

CDIP1 is a p53-inducible proapoptotic transmembrane protein that transduces death signals from genotoxic and ER stress to mitochondria via the extrinsic apoptotic pathway. Upon induction, CDIP1 interacts with BAP31 at the ER membrane, triggering BAP31 cleavage, caspase-8 activation, generation of truncated Bid (tBid), and BAX oligomerization at mitochondria; CDIP1 knockout mice confirm its essential role in ER-stress-mediated apoptosis (PMID:24139803). CDIP1 also engages ESCRT-I (via Ca²⁺-dependent ALG-2 binding) and ER-resident VAP proteins through an FFAT-like motif to potentiate caspase-3/7-dependent cell death, while CDK5-mediated phosphorylation at Ser-32 and lysosomal degradation regulate its abundance and activity (PMID:33503978, PMID:38928226). Beyond apoptosis, CDIP1 drives TNF-α upregulation downstream of p53 to sensitize cells to TNF-α-induced death (PMID:17599062, PMID:22549949) and functions as an alternative host cell-surface receptor for Bacillus cereus hemolysin BL toxin (PMID:32544461).

1. 2007 High

   Identification of CDIP1 as a direct p53 transcriptional target established a new link between the p53 tumor-suppressor network and the extrinsic apoptotic pathway, showing that CDIP1-dependent death requires caspase-8 and drives TNF-α upregulation.

   Evidence siRNA knockdown, overexpression, luciferase reporter, caspase-8 inhibition in human cell lines

   PMID:17599062

   Open questions at the time

   • Mechanism by which CDIP1 induces TNF-α expression is not defined
   • Direct versus indirect transcriptional control of TNF-α by CDIP1 not resolved
2. 2012 Medium

   Demonstrating that endogenous CDIP1 sensitizes cancer cells to TNF-α-induced apoptosis in vitro and in vivo clarified CDIP1 as a functional determinant of cell fate in the p53–TNF-α axis.

   Evidence siRNA knockdown, overexpression, tumor xenograft models, cell viability assays

   PMID:22549949

   Open questions at the time

   • Molecular mechanism of TNF-α sensitization (receptor-level vs. intracellular) not dissected
   • Findings from a single laboratory
3. 2013 High

   Showing that CDIP1 physically binds BAP31 at the ER and drives BAP31 cleavage, tBid generation, caspase-8 activation, and BAX oligomerization — confirmed by impaired ER-stress apoptosis in CDIP1 knockout mice — resolved the molecular route by which ER stress signals are relayed to mitochondria through CDIP1.

   Evidence Reciprocal co-immunoprecipitation, in vitro binding, CDIP1 knockout mice, caspase and BAX oligomerization assays

   PMID:24139803

   Open questions at the time

   • Structural basis of the CDIP1–BAP31 interaction is unknown
   • Whether CDIP1 integrates additional ER-stress sensors upstream is unresolved
4. 2020 High

   A genome-wide CRISPR screen revealed an unexpected non-apoptotic function: CDIP1 serves as an alternative host cell-surface receptor for Bacillus cereus hemolysin BL, functionally distinct from but related to LITAF.

   Evidence Genome-wide CRISPR-Cas9 knockout screen in LITAF-deficient cells, toxin challenge, in vivo mouse model

   PMID:32544461

   Open questions at the time

   • Structural determinants of CDIP1–HBL binding are not characterized
   • Whether toxin binding co-opts CDIP1's apoptotic signaling remains unknown
5. 2021 Medium

   Identification of Ca²⁺-dependent ALG-2 and ESCRT-I (TSG101/VPS37B/C) interactions, together with VAP protein binding through an FFAT-like motif, expanded the CDIP1 interactome and showed that these partners potentiate caspase-3/7-mediated death, linking CDIP1 to ER–endosome membrane contact site machinery.

   Evidence Co-immunoprecipitation of GFP-CDIP1, FFAT-motif mutagenesis, caspase-3/7 activity assays

   PMID:33503978

   Open questions at the time

   • Functional significance of ESCRT-I engagement (membrane remodeling vs. signaling platform) not determined
   • Endogenous validation of ALG-2–CDIP1 complex is lacking
   • Single laboratory findings
6. 2021 Medium

   Showing that exosomal miR-21-5p silences CDIP1 to suppress caspase-3 activation and apoptosis in cardiac endothelial cells placed CDIP1 within a clinically relevant post-transcriptional regulatory circuit in ischemic heart disease.

   Evidence Small RNA sequencing, miRNA transfection, rat myocardial infarction model

   PMID:33391474

   Open questions at the time

   • Whether miR-21-5p regulation of CDIP1 operates broadly or is restricted to cardiac endothelium is unclear
   • Single laboratory
7. 2024 Medium

   Demonstrating CDK5-dependent phosphorylation at Ser-32, lysosomal degradation, and a cytoprotective autophagy response prior to apoptosis revealed post-translational and autophagic control layers that tune CDIP1 pro-death activity.

   Evidence Roscovitine treatment, S32D phosphomimetic mutagenesis, VPS34 inhibitor SAR405, autophagy and apoptosis assays in MCF-7 cells

   PMID:38928226

   Open questions at the time

   • Direct CDK5 phosphorylation of CDIP1 at Ser-32 has not been demonstrated by in vitro kinase assay
   • Mechanism by which CDIP1 triggers autophagy is undefined
   • Single laboratory, single cell line

• The structural basis of CDIP1 interactions with BAP31, ESCRT-I, and HBL toxin remains unresolved, and the mechanistic link between CDIP1's roles in apoptosis signaling and its function as a toxin receptor has not been established.
• No structural or cryo-EM data for any CDIP1 complex
• Relationship between toxin receptor and apoptotic functions is unexplored
• Physiological role of CDK5-mediated Ser-32 phosphorylation in vivo is unknown