Phospholipase-C sensitive GPI-anchored proteins of goat sperm: possible role in sperm protection

Serine protease PRSS55 is crucial for male mouse fertility via affecting sperm migration and sperm-egg binding

Testis-specific PRSS55 is a highly conserved chymotrypsin-like serine protease among mammalian species. So far, the physiological function of PRSS55 remains unknown. Here, we show that PRSS55 is a GPI-anchored membrane protein, specifically expressed in adult mouse testis and mainly observed in the luminal side of seminiferous tubules and sperm acrosome. Mice deficient for Prss55 develop male infertile with normal reproduction-related parameters observed. Interestingly, in vivo fertilization rate of Prss55^−/− males is dramatically decreased, possibly due to incapable migration of Prss55^−/− sperm from uterus into oviduct. However, in vitro fertilization rate has no difference between two genotypes although Prss55^−/− sperm presents defective recognition/binding to zona-intact or zona-free oocytes. Further study reveals that mature ADAM3 is almost undetectable in Prss55^−/− sperm, while precursor ADAM3 remains unchanged in the testis. However, it is shown that ADAM3 has no interaction with PRSS55 by immunoprecipitation with anti-PRSS55 antibody. The expression levels of several proteins known to be related to the observed phenotypes remain comparable between wt and Prss55^−/− mice. Moreover, we found that Prss55 deficiency has no effect on PRSS37 or vice versa albeit two mutant males share almost the same phenotypes. Microarray analysis reveals a total of 72 differentially expressed genes in Prss55^−/− testis, most of which are associated with cellular membrane and organelle organization, protein transport and complex assembly, and response to stimulus and signaling. In conclusion, we have demonstrated that PRSS55 plays vital roles in regulating male fertility of mice, including in vivo sperm migration and in vitro sperm–egg interaction, possibly by affecting the maturation of ADAM3 in sperm and the expression of multiple genes in testis.

Enhanced phosphorylation of caveolar PKC-α limits peptide internalization in lung endothelial cells

We previously reported that the vasoactive peptide 1 (P1, "SSWRRKRKESS") modulates the tension of pulmonary artery vessels through caveolar endothelial nitric oxide synthase (eNOS) activation in intact lung endothelial cells (ECs). Since PKC-α is a caveolae resident protein and caveolae play a critical role in the peptide internalization process, we determined whether modulation of caveolae and/or caveolar PKC-α phosphorylation regulates internalization of P1 in lung ECs. Cell monolayers were incubated in culture medium containing Rhodamine red-labeled P1 (100 μM) for 0-120 min. Confocal examinations indicate that P1 internalization is time-dependent and reaches a plateau at 60 min. Caveolae disruption by methyl-β-cyclodextrin (CD) and filipin (FIL) inhibited the internalization of P1 in ECs suggesting that P1 internalizes via caveolae. P1-stimulation also enhances phosphorylation of caveolar PKC-α and increases intracellular calcium (Ca(2+)) release in intact cells suggesting that P1 internalization is regulated by PKC-α in ECs. To confirm the roles of increased phosphorylation of PKC-α and Ca(2+) release in internalization of P1, PKC-α modulation by phorbol ester (PMA), PKC-α knockdown, and Ca(2+) scavenger BAPTA-AM model systems were used. PMA-stimulated phosphorylation of caveolar PKC-α is associated with significant reduction in P1 internalization. In contrast, PKC-α deficiency and reduced phosphorylation of PKC-α enhanced P1 internalization. P1-mediated increased phosphorylation of PKC-α appears to be associated with increased intracellular calcium (Ca(2+)) release since the Ca(2+) scavenger BAPTA-AM enhanced P1 internalization. These data indicate that caveolar integrity and P1-mediated increased phosphorylation of caveolar PKC-α play crucial roles in the regulation of P1 internalization in lung ECs.

Characterization of lactoferrin receptor on human spermatozoa

Lactoferrin (LF) is abundant in human seminal plasma and on sperm surfaces. However, lactoferrin receptor (LFR) on human spermatozoa has not yet been reported. To study the expression, localization and characteristics of LFR on human spermatozoa, different experimental approaches were applied: LFR gene was amplified from a human testis cDNA library and recombinant LFR (rLFR) protein was produced in the expression vector Escherichia coli BL21 (DE3); human sperm membrane proteins were extracted and analysed via Western blot; the binding of LF to LFR was investigated by Far-Western blot, immunoprecipitation and autoradiography analysis and the localization of LFR on sperm surfaces was detected using immunofluorescence. LFR gene was amplified from a human testis cDNA library and the molecular weight of rLFR was 34kDa. The native LFR on human spermatozoa was a 136-kDa tetramer which was anchored to the sperm head and mid-piece through glycophosphatidylinositol. LF could bind to LFR competitively in vitro. As far as is known, this study has elucidated for the first time that LFR was expressed at the testis level, was anchored to the sperm membrane by glycophosphatidylinositol during spermatogenesis. LFR may play important roles through binding to and mediating LF.