GUCA2A

GUCA2A (guanylin) is an intestinal peptide hormone that signals through the receptor guanylate cyclase GUCY2C (GC-C) to control epithelial fluid and electrolyte homeostasis (PMID:9344659). Binding of guanylin to GC-C stimulates an increase in intracellular cyclic GMP and drives chloride secretion through CFTR (PMID:9344659). Beyond its secretory role, this ligand-receptor axis functions as a tumor-suppressor pathway in the colon: GUCA2A expression is lost in tubular adenomas, serrated adenomas, and MSI colorectal tumors, and this loss silences GUCY2C signaling (PMID:30716341). The available corpus contains no further mechanistic dissection of guanylin processing, receptor binding kinetics, or downstream signaling.

1. 1997 Medium

   Established guanylin as a ligand for the intestinal receptor guanylate cyclase-C, defining the molecular basis of its secretory action.

   Evidence Gene cloning, chromosomal mapping, and mRNA expression analysis linking Guca2/GUCA2A to GC-C activation in mouse

   PMID:9344659

   Open questions at the time

   • Receptor activation mechanism inferred from prior biochemistry rather than directly reconstituted
   • No structural characterization of the guanylin-GC-C interaction
   • Peptide maturation and processing not addressed
2. 2019 Medium

   Placed GUCA2A within a colonic tumor-suppressor axis by showing its loss across multiple neoplastic subtypes silences GUCY2C signaling.

   Evidence Immunohistochemistry of human tumor specimens plus genetic mouse models and loss-of-function pathway analysis

   PMID:30716341

   Open questions at the time

   • Causal mechanism of GUCA2A loss driving tumorigenesis not dissected
   • Therapeutic hormone-replacement reactivation of GUCY2C is proposed but not demonstrated functionally
   • No quantification of cGMP/CFTR output in tumor versus normal tissue
3. 2023 Low

   Identified GUCA2A as a selective Paneth cell marker, refining the cellular source of the hormone in human intestine.

   Evidence Immunohistochemistry with semi-automated digital image analysis on resected intestinal tissue from 70 infants

   PMID:37017768

   Open questions at the time

   • Single study, single method (IHC) without functional consequence for GUCA2A itself
   • Relationship between Paneth cell GUCA2A and the colonocyte secretory pool unresolved
4. 2025 Low

   Identified KLF4 as an upstream transcription factor sufficient to specify GUCA2A-expressing colonocytes.

   Evidence Doxycycline-inducible lentiviral KLF4 overexpression in human colonoids (preprint), using GUCA2A as a lineage marker

   Open questions at the time

   • Single preprint overexpression experiment; not independently confirmed
   • Direct versus indirect transcriptional control of the GUCA2A promoter by KLF4 not established
   • Physiological relevance to endogenous cell specification untested

• How GUCA2A loss is mechanistically coupled to colorectal tumorigenesis and whether hormone replacement can restore GUCY2C signaling remain open.
• No demonstration that restoring GUCA2A reverses neoplastic phenotypes
• Signaling output downstream of cGMP in the tumor-suppressor context uncharacterized