CLCA4

CLCA4 is a self-cleaving metalloprotease that operates both as a modulator of epithelial chloride transport and as a suppressor of epithelial-to-mesenchymal transition (EMT) (PMID:38825009, PMID:24386311). Its secreted N-terminal fragment (N-CLCA4) potentiates Ca2+-activated Cl- currents carried specifically by TMEM16B; this activity maps to the von Willebrand factor type A (VWA) domain and depends on the metal ion-dependent adhesion site (MIDAS) motif within it, defining a CLCA4/TMEM16B pairing distinct from the CLCA1/TMEM16A pairing (PMID:38825009). In epithelial and multiple cancer contexts, CLCA4 maintains epithelial identity: its loss downregulates E-cadherin and upregulates mesenchymal markers, and reciprocal gain/loss-of-function across bladder, hepatocellular, and colorectal cancer cells shows that CLCA4 inhibits proliferation, migration, and invasion by suppressing PI3K/AKT signaling and the associated EMT program (PMID:24386311, PMID:29190973, PMID:30312171, PMID:31164625). CLCA4 expression is post-transcriptionally repressed through direct targeting of its mRNA by miR-19a in colorectal cancer, with the miR-19a/CLCA4 axis modulating PI3K/AKT activation (PMID:35266369).

1. 2012 Low

   Whether CLCA4 contributes to epithelial chloride handling was unresolved; a genetic association in cystic fibrosis patients linked CLCA4 promoter variants to residual Ca2+-mediated colonic chloride secretion, providing the first human evidence tying CLCA4 to chloride transport modulation.

   Evidence Association study with fine-mapping in 171 CF patients stratified by residual chloride conductance

   PMID:23073314

   Open questions at the time

   • Genetic association only, with no direct functional experiment on the protein
   • Causal mechanism linking the variant to chloride secretion not established
   • No molecular partner identified
2. 2013 Medium

   The cellular role of CLCA4 was undefined; shRNA knockdown in mammary epithelial cells showed it is required to maintain epithelial identity and suppress EMT, establishing CLCA4 as a guardian of the epithelial state.

   Evidence shRNA knockdown with EMT marker profiling in immortalized mammary epithelial cells; double knockdown with CLCA2

   PMID:24386311

   Open questions at the time

   • No signaling pathway placed downstream of CLCA4
   • Distinction between CLCA2 and CLCA4 roles not mechanistically resolved
   • Single lab, single cell context
3. 2017 Medium

   The signaling axis through which CLCA4 suppresses invasion was unknown; reciprocal gain/loss-of-function in bladder cancer placed CLCA4 upstream of PI3K/AKT, connecting its EMT-suppressing role to a defined oncogenic pathway.

   Evidence Overexpression and siRNA knockdown with proliferation/migration/invasion assays and Western blot for PI3K/AKT phosphorylation and EMT markers

   PMID:29190973

   Open questions at the time

   • Mechanism by which CLCA4 inhibits PI3K/AKT not defined
   • No direct molecular interaction demonstrated
   • Single cancer type, single lab
4. 2018 Medium

   Whether the PI3K/AKT-suppressing role generalized beyond bladder cancer was open; hepatocellular carcinoma experiments confirmed CLCA4 suppresses EMT and PI3K/AKT phosphorylation across a second tumor context.

   Evidence siRNA knockdown and overexpression with migration/invasion assays and Western blot for PI3K/AKT and EMT markers in HCC cells

   PMID:30312171

   Open questions at the time

   • Direct biochemical link between CLCA4 and PI3K/AKT remains unestablished
   • No structural or domain mapping of the suppressive activity
5. 2019 Medium

   The generality of CLCA4's tumor-suppressive function was further tested in colorectal cancer, where overexpression inhibited migration and invasion via PI3K/AKT-dependent EMT suppression, reinforcing a conserved mechanism.

   Evidence Gain-of-function colorectal cancer models with wound healing, Transwell, and Western blot for PI3K/AKT and EMT markers

   PMID:31164625

   Open questions at the time

   • Loss-of-function not paired in this study
   • No in vivo validation in this context
   • Single lab
6. 2020 Medium

   How CLCA4 expression is controlled in cancer was unknown; luciferase and rescue experiments identified CLCA4 as a direct target of miR-19a (colorectal) and miR-501-5p (HNSCC), establishing post-transcriptional repression as a route to CLCA4 loss and PI3K/AKT activation in tumors.

   Evidence Luciferase reporter assays, miRNA mimic/inhibitor transfection, CLCA4 knockdown rescue, Western blot for PI3K/AKT

   PMID:32072405 PMID:35266369

   Open questions at the time

   • miR-501-5p axis has limited functional follow-up and is Low-confidence
   • Whether these miRNAs regulate CLCA4 in normal epithelium not tested
   • Upstream control of the miRNAs themselves not addressed
7. 2021 Low

   Whether CLCA4 suppresses tumor growth in vivo was untested; esophageal carcinoma xenografts showed CLCA4 overexpression inhibits proliferation, invasion, EMT, and tumor growth, extending the in vitro tumor-suppressor role to an animal model.

   Evidence CCK-8, Transwell, Western blot for EMT markers, and xenograft tumor model in esophageal carcinoma cells

   PMID:34194494

   Open questions at the time

   • No pathway mechanism beyond EMT description in this study
   • Single lab, single tumor type
8. 2024 High

   The biochemical activity of CLCA4 itself was undefined; electrophysiology with domain truncation and MIDAS mutagenesis showed CLCA4 is a self-cleaving metalloprotease whose secreted VWA-domain-bearing N-fragment potentiates TMEM16B (not TMEM16A) currents through the MIDAS motif, defining its molecular mechanism and ion-channel partner specificity.

   Evidence ICaCC electrophysiology in HEK293T cells with domain deletion constructs, MIDAS mutagenesis, and cell-surface engagement assays

   PMID:38825009

   Open questions at the time

   • Link between TMEM16B potentiation and the PI3K/AKT/EMT tumor-suppressor role not established
   • Endogenous physiological tissue context of CLCA4/TMEM16B pairing not defined
   • No structural model of the N-CLCA4/TMEM16B interaction

• It remains unknown how CLCA4's metalloprotease/TMEM16B-potentiating activity mechanistically connects to its PI3K/AKT-dependent suppression of EMT, and whether the secreted N-CLCA4 fragment mediates the tumor-suppressive phenotype.
• No experiment links the channel-modulating activity to PI3K/AKT signaling
• Direct binding partners in the EMT pathway unidentified
• Whether protease activity is required for tumor suppression untested