CAPZA1

CAPZA1 is the α1 subunit of the heterodimeric CapZ capping protein that binds barbed ends of F-actin filaments to restrain actin polymerization; its loss or displacement promotes cytoskeletal remodeling, epithelial–mesenchymal transition, invadopodia formation, and enhanced cell migration and invasion (PMID:28093067, PMID:35096613, PMID:40796418). CAPZA1 capping activity is negatively regulated by PIP2, which binds CAPZA1 and releases it from barbed ends under hypoxic signaling through HIF-1α/RhoA/ROCK1 (PMID:30742939), and by the FAM21C CPI domain (PMID:35096613), while protein turnover is controlled by UBR5-mediated ubiquitin-proteasome degradation (PMID:33777788). Beyond its cytoskeletal role, nuclear CAPZA1 binds LRP1 intracellular domain to suppress LAMP1 transcription and autolysosome formation, thereby impairing autophagic clearance of H. pylori CagA oncoprotein—a function amplified by HDAC-inhibitor-driven or oxidative-stress-driven transcriptional upregulation of CAPZA1 (PMID:30176157, PMID:31146068, PMID:41586340). In spermatogenesis, CAPZA1 is required for normal flagellar fibrous-sheath assembly and sperm motility, with its deficiency disrupting axonemal architecture and thiol homeostasis via reduced p300/SLC7A11 signaling (PMID:41858859).

1. 2017 Medium

   Establishing that CAPZA1 directly caps actin barbed ends in epithelial cells and that its loss is sufficient to drive EMT and invasive behavior answered whether the α1 capping-protein subunit has a tumor-suppressive cytoskeletal function.

   Evidence Co-IP of CAPZA1–actin; siRNA/overexpression in HCC cells with transwell assays and orthotopic xenograft imaging

   PMID:28093067

   Open questions at the time

   • In vitro capping kinetics for CAPZA1 vs. CAPZA2 subunit isoforms not measured
   • Structural basis of CAPZA1–barbed-end interaction not resolved
   • Contribution of CAPZB partner subunit to observed phenotypes not dissected
2. 2018 Medium

   Discovery that CAPZA1 translocates to the nucleus and suppresses LAMP1 transcription by sequestering LRP1-ICD from the LAMP1 promoter revealed an unexpected non-cytoskeletal function in autophagy regulation relevant to H. pylori-driven gastric carcinogenesis.

   Evidence Co-IP of CAPZA1–LRP1-ICD; ChIP of LRP1-ICD at LAMP1 promoter; autolysosome and CagA degradation readouts in gastric epithelial cells

   PMID:30176157

   Open questions at the time

   • Mechanism of CAPZA1 nuclear import not identified
   • Whether CAPZA1 nuclear function occurs outside H. pylori infection context unknown
   • Single-lab finding without independent replication
3. 2019 Medium

   Two studies clarified upstream regulation of CAPZA1: PIP2 was shown to bind CAPZA1 and displace it from barbed ends under hypoxia (via HIF-1α/RhoA/ROCK1), and oxidative stress was shown to upregulate CAPZA1 transcription through enhanced histone H3 acetylation at its promoter, linking environmental signals to both capping-activity removal and CAPZA1 abundance.

   Evidence Co-IP of PIP2–CAPZA1 with pharmacological inhibitors in HCC cells plus xenograft; ChIP for H3 acetylation at CAPZA1 promoter in H. pylori-infected gastric cells and Mongolian gerbil model

   PMID:30742939 PMID:31146068

   Open questions at the time

   • Direct binding affinity of PIP2 for CAPZA1 not quantified biophysically
   • Specific histone acetyltransferase responsible for CAPZA1 promoter acetylation not identified at the time
   • Interplay between PIP2-mediated displacement and transcriptional regulation not examined
4. 2021 Medium

   Identification of UBR5 as the E3 ligase targeting CAPZA1 for proteasomal degradation established a post-translational mechanism controlling CAPZA1 protein levels and linked CAPZA1 to pancreatic cancer cell motility downstream of UBR5.

   Evidence AP-MS identification of CAPZA1 as UBR5 substrate; epistasis rescue with CAPZA1 siRNA; in vivo liver metastasis model

   PMID:33777788

   Open questions at the time

   • Specific ubiquitination sites on CAPZA1 not mapped
   • Whether UBR5-mediated degradation is tissue-specific or general not determined
   • No deubiquitinase for CAPZA1 identified
5. 2022 Medium

   Demonstrating that FAM21C inhibits CAPZA1 capping activity through its CPI domain defined a protein-level inhibitor distinct from PIP2 and connected WASH complex-associated actin regulation to CAPZA1 function in cancer invasion.

   Evidence Co-IP with CPI-domain mutant rescue; transwell and xenograft metastasis assays in HCC cells

   PMID:35096613

   Open questions at the time

   • Whether FAM21C and PIP2 compete for the same binding surface on CAPZA1 not tested
   • Direct capping activity measurement (e.g., pyrene-actin assay) not reported
   • Single-lab study
6. 2025 Medium

   Two discoveries expanded transcriptional and metabolic regulation: TGF-β was shown to suppress CAPZA1 via GATA3 downregulation (promoting invadopodia), and short-chain fatty acids were shown to induce CAPZA1 overexpression via HDAC inhibition (promoting CagA accumulation and stemness), demonstrating context-dependent oncogenic versus tumor-suppressive consequences of CAPZA1 levels.

   Evidence ChIP for GATA3 at CAPZA1 promoter with invadopodia assays and in vivo SB431542 treatment; HDAC inhibition in gastric organoids, cell lines, and mouse infection models with metabolite and microbiota profiling

   PMID:40796418 PMID:41586340

   Open questions at the time

   • Whether GATA3 and HDAC-dependent regulation of CAPZA1 operate in the same tissue contexts is unclear
   • Relative contribution of CAPZA1 cytoskeletal versus nuclear functions to net phenotype not parsed
   • No genome-wide identification of other transcription factors at the CAPZA1 promoter
7. 2026 Medium

   Two studies extended CAPZA1 biology to spermatogenesis and post-transcriptional regulation: CAPZA1 loss-of-function disrupts flagellar fibrous sheath assembly and thiol homeostasis via p300/SLC7A11, while a 3′UTR SNP (rs373245753) switches allele-specific RNA-binding protein recruitment (hnRNP K/PTBP1 vs. UPF1), controlling mRNA stability and tumor-suppressive capacity.

   Evidence WES identification of homozygous missense mutation; CRISPR KO in mouse spermatids with TEM and ELISA; biotin-RNA pulldown/MS and RIP with mRNA decay assays in ESCC cells plus xenograft

   PMID:41787560 PMID:41858859

   Open questions at the time

   • Whether flagellar defect reflects CAPZA1 capping activity or a scaffolding function not resolved
   • Frequency and population genetics of rs373245753 not characterized broadly
   • Both findings from single labs without independent replication

• Key unresolved questions include the structural basis of CAPZA1-specific functions versus other α-subunit isoforms, the mechanism of CAPZA1 nuclear import, whether cytoskeletal and nuclear roles are coordinated or independent, and whether CAPZA1 loss-of-function mutations cause a defined Mendelian fertility disorder.
• No crystal structure of full-length human CAPZA1 in complex with actin barbed end
• Nuclear localization signal or import chaperone not identified
• Isoform-specific (CAPZA1 vs. CAPZA2) phenotypes not systematically compared
• Whether human CAPZA1 mutations cause asthenozoospermia as a Mendelian trait requires family-based confirmation