From prediction to experimental validation: desmoglein 2 is a functionally relevant substrate of matriptase in epithelial cells and their reciprocal relationship is important for cell adhesion.

Accurate identification of substrates of a protease is critical in defining its physiological functions. We previously predicted that Dsg-2 (desmoglein-2), a desmosomal protein, is a candidate substrate of the transmembrane serine protease matriptase. The present study is an experimental validation of this prediction. As demanded by our published method PNSAS [Prediction of Natural Substrates from Artificial Substrate of Proteases; Venkatraman, Balakrishnan, Rao, Hooda and Pol (2009) PLoS ONE 4, e5700], this enzyme-substrate pair shares a common subcellular distribution and the predicted cleavage site is accessible to the protease. Matriptase knock-down cells showed enhanced immunoreactive Dsg-2 at the cell surface and formed larger cell clusters. When matriptase was mobilized from intracellular storage deposits to the cell surface there was a decrease in the band intensity of Dsg-2 in the plasma membrane fractions with a concomitant accumulation of a cleaved product in the conditioned medium. The exogenous addition of pure active recombinant matriptase decreased the surface levels of immunoreactive Dsg-2, whereas the levels of CD44 and E-cadherin were unaltered. Dsg-2 with a mutation at the predicted cleavage site is resistant to cleavage by matriptase. Thus Dsg-2 seems to be a functionally relevant physiological substrate of matriptase. Since breakdown of cell-cell contact is the first major event in invasion, this reciprocal relationship is likely to have a profound role in cancers of epithelial origin. Our algorithm has the potential to become an integral tool for discovering new protease-substrate pairs.

Factor VIII gene polymorphisms in North Indian population: a consensus algorithm for carrier analysis of hemophilia A.

BACKGROUND: Hemophilia A, an X-linked recessive disorder, has the prevalence of 1 male per 7000 of the male population in the Northern states of India. The aim of the present study was to analyze the polymorphisms of the factor VIII gene in a sample population comprised of 22 families (112 persons) in order to formulate an algorithm that would be informative and accurate, yet cost-effective for carrier diagnosis. METHODS: Polymerase chain reaction was used to study the polymorphisms of two intragenic restriction fragment length polymorphic sites (recognized by BclI and HindIII) and an extragenic variable number tandem repeat (VNTR) locus (St14). RESULTS: Fifty-eight percent of the women tested were heterozygous for the BclI restriction fragment length polymorphism (RFLP) (significantly high compared to earlier reports), signifying the usefulness of this marker in carrier detection. About 64% of the families from the target population could be diagnosed using this marker alone. The other intragenic HindIII RFLP site showed a heterozygosity rate of 43% in women, and was effective in diagnosing 50% of the families studied. The population prevalence for '+' alleles of BclI and HindIII were 68% and 33%, respectively. About 88% of the women tested were heterozygous for the St14 locus, and 83% of the families could be diagnosed using this marker alone. The 1390- and 1300-bp alleles were most prevalent, while novel polymorphisms of 1500 and 1345 bp were detected. CONCLUSIONS: Based on the above data, we suggest screening hemophilic families first for BclI polymorphism, followed by an analysis for HindIII polymorphism in case of homozygosity at the BclI site. When both were noninformative, analysis of St14 locus would be necessary.

Platelet storage under in vitro condition is associated with calcium-dependent apoptosis-like lesions and novel reorganization in platelet cytoskeleton.

Platelets are cleared from circulation after a life span of 8-10 days. The molecular mechanisms underlying platelet senescence remain poorly characterized. Here we report that, progressive functional impairment in the platelets incubated in vitro in a plasma-free isotonic medium for up to 24 h at 37 degrees C is associated with release of cytochrome c from platelet mitochondria and cleavage of procaspase-9, but without evidence of caspase-3 activation. Concomitantly, there was proteolysis of survival proteins like focal adhesion kinase, Src, gelsolin, and specific cytoskeleton-associated peptides, in a manner regulated by extracellular calcium and calpain activity. Cytoskeleton played a critical role as evidenced from the association of these proteins and their degradation products, as well as procaspase-3 and the actin regulatory small GTPase, CDC42Hs, with the cytoskeleton of the stored platelets. The cytoskeletal enrichment with specific proteins was not associated with increase in the content of F-actin and was cytochalasin-resistant, thus signifying a novel mechanism of interaction of the translocating proteins with the pre-existing cytoskeleton. There was progressive exposure of phosphatidylserine on the outer leaflet of platelet membrane and specific electron microscopic changes suggestive of apoptotic lesions. Based on these observations we discuss the caspase-independent but calpain-mediated signaling events in the stored platelets resembling the features of apoptosis in the nucleated cells.