Identification of human zonulin, a physiological modulator of tight junctions, as prehaptoglobin-2.
Increased intestinal permeability (IP) has emerged recently as a common underlying mechanism in the pathogenesis of allergic, inflammatory, and autoimmune diseases. The characterization of zonulin, the only physiological mediator known to regulate IP reversibly, has remained elusive. Through proteomic analysis of human sera, we have now identified human zonulin as the precursor for haptoglobin-2 (pre-HP2). Although mature HP is known to scavenge free hemoglobin (Hb) to inhibit its oxidative activity, no function has ever been ascribed to its uncleaved precursor form. We found that the single-chain zonulin contains an EGF-like motif that leads to transactivation of EGF receptor (EGFR) via proteinase-activated receptor 2 (PAR(2)) activation. Activation of these 2 receptors was coupled to increased IP. The siRNA-induced silencing of PAR(2) or the use of PAR(2)(-/-) mice prevented loss of barrier integrity. Proteolytic cleavage of zonulin into its alpha(2)- and beta-subunits neutralized its ability to both activate EGFR and increase IP. Quantitative gene expression revealed that zonulin is overexpressed in the intestinal mucosa of subjects with celiac disease. To our knowledge, this is the initial example of a molecule that exerts a biological activity in its precursor form that is distinct from the function of its mature form. Our results therefore characterize zonulin as a previously undescribed ligand that engages a key signalosome involved in the pathogenesis of human immune-mediated diseases that can be targeted for therapeutic interventions.
Tripathi
Amit
A
Mucosal Biology Research Center, Center for Vascular and Inflammatory Diseases and Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 20201, USA.
Lammers
Karen M
KM
Goldblum
Simeon
S
Shea-Donohue
Terez
T
Netzel-Arnett
Sarah
S
Buzza
Marguerite S
MS
Antalis
Toni M
TM
Vogel
Stefanie N
SN
Zhao
Aiping
A
Yang
Shiqi
S
Arrietta
Marie-Claire
MC
Meddings
Jon B
JB
Fasano
Alessio
A
D000818:Animals; D002772:Cholera Toxin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006242:Haptoglobins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D051379:Mice; D010539:Permeability; D011498:Protein Precursors / Q000737:chemistry* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D019108:Tight Junctions / Q000378:metabolism*
D006242:Haptoglobins; D011498:Protein Precursors; D012333:RNA, Messenger; D011994:Recombinant Proteins; C408043:zonulin; D002772:Cholera Toxin