title: Functional analysis of a pancreatic secretory trypsin inhibitor-like protein in insects: silencing effects resemble the human pancreatic autodigestion phenotype.
abstract: BACKGROUND
  In mammalian pancreatic cells, the pancreatic secretory trypsin inhibitor (PSTI) prevents the premature activation of digestive enzymes and thus plays an important role in a protective mechanism against tissue destruction by autophagy, a process which may ultimately cause diseases such as pancreatitis and pancreatic cancer. Insects, however, lack a pancreas and so far no PSTI-like peptides are functionally characterized.
  
  
  RESULTS
  In several insect species protease inhibitors that structurally resemble the mammalian PSTI were predicted in silico. A putative PSTI-like protein (LmPSTI) was cloned and sequenced in the African migratory locust, Locusta migratoria. For the first time the expression of an insect derived PSTI-like inhibitor was shown to be restricted to the digestive enzyme-producing organs in insects (midgut and caeca). LmPSTI was produced via a bacterial expression system and was found to be a potent inhibitor of bovine trypsin as well as endogenous locust gut enzymes. In the caeca, RNAi-mediated knockdown of LmPSTI resulted in a significantly upregulated expression (2-fold) of locust ATG8 transcripts (an ubiquitin-like protein crucial for autophagosome formation). These findings were confirmed by an ultrastructural study on caeca, revealing the presence of autophagy-related structures in RNAi-treated animals.
  
  
  CONCLUSIONS
  The results of this study lead us to believe that LmPSTI plays an important role in controlling the proteolytic activity in the digestive system of L. migratoria. These findings provide new evidence for the existence of an ancient protective mechanism in metazoan digestive systems and open new perspectives for the study of autophagy-related diseases in the digestive tract.
authors.affiliation: Department of Animal Physiology and Neurobiology, Zoological Institute K.U. Leuven, Naamsestraat 59, B-3000 Leuven, Belgium. Vincent.vanhoef@bio.kuleuven.be
authors.forename: Vincent
authors.initials: V
authors.lastname: van Hoef
authors.forename: Bert
authors.initials: B
authors.lastname: Breugelmans
authors.forename: Jornt
authors.initials: J
authors.lastname: Spit
authors.forename: Gert
authors.initials: G
authors.lastname: Simonet
authors.forename: Sven
authors.initials: S
authors.lastname: Zels
authors.forename: Johan
authors.initials: J
authors.lastname: Billen
authors.forename: Jozef
authors.initials: J
authors.lastname: Vanden Broeck
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D004064:Digestive System / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D048188:Locusta migratoria / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D016415:Sequence Alignment; D014361:Trypsin Inhibitors / Q000235:genetics* / Q000378:metabolism; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism
chemical_list: D019476:Insect Proteins; D014361:Trypsin Inhibitors; D014452:Ubiquitins