cDNA cloning and expression of a novel serine protease in the mouse brain

Testosterone regulates granzyme K expression in rat testes

OBJECTIVE

Testosterone depletion induces increased germ cell apoptosis in testes. However, limited studies exist on genes that regulate the germ cell apoptosis. Granzymes (GZM) are serine proteases that induce apoptosis in various tissues. Multiple granzymes, including GZMA, GZMB and GZMN, are present in testes. Th us, we investigated which granzyme may be testosterone responsive and possibly may have a role in germ cell apoptosis aft er testosterone depletion.

METHODS

Ethylene dimethane sulfonate (EDS), a toxicant that selectively ablates the Leydig cells, was injected into rats to withdraw the testosterone. The testosterone depletion effects after 7 days post-EDS were verified by replacing the testosterone exogenously into EDS-treated rats. Serum or testicular testosterone was measured by radioimmunoassay. Using qPCR, mRNAs of granzyme variants in testes were quantified. The germ cell apoptosis was identified by TUNEL assay and the localization of GZMK was by immunohistochemistry.

RESULTS

EDS treatment eliminated the Leydig cells and depleted serum and testicular testosterone. At 7 days post-EDS, testis weights were reduced 18% with increased germ cell apoptosis plus elevation GZMK expression. GZMK was not associated with TUNEL-positive cells, but was localized to stripped cytoplasm of spermatids. In addition, apoptotic round spermatids were observed in the caput epididymis.

CONCLUSIONS

GZMK expression in testes is testosterone dependent. GZMK is located adjacent to germ cells in seminiferous tubules and the presence of apoptotic round spermatids in the epididymis suggest its role in the degradation of microtubules in ectoplasmic specializations. Thus, overexpression of GZMK may indirectly regulate germ cell apoptosis by premature release of round spermatids from seminiferous tubule lumen.

Death by a thousand cuts: granzyme pathways of programmed cell death

The granzymes are cell death-inducing enzymes, stored in the cytotoxic granules of cytotoxic T lymphocytes and natural killer cells, that are released during granule exocytosis when a specific virus-infected or transformed target cell is marked for elimination. Recent work suggests that this homologous family of serine esterases can activate at least three distinct pathways of cell death. This redundancy likely evolved to provide protection against pathogens and tumors with diverse strategies for evading cell death. This review discusses what is known about granzyme-mediated pathways of cell death as well as recent studies that implicate granzymes in immune regulation and extracellular proteolytic functions in inflammation.

Resuscitating mutations in a furin cleavage-deficient mutant of the flavivirus tick-borne encephalitis virus

Cleavage of the viral surface protein prM by the proprotein convertase furin is a key step in the maturation process of flavivirus particles. A mutant of tick-borne encephalitis virus (TBEV) carrying a deletion mutation within the furin recognition motif of protein prM (changing R-T-R-R to R-T-R) was previously shown to be noninfectious in BHK-21 cells. We now demonstrate how natural selection can overcome this lethal defect in two different growth systems by distinct resuscitating mutations. In BHK-21 cells, a spontaneous codon duplication created a minimal furin cleavage motif (R-R-T-R). This mutation restored infectivity by enabling intracellular prM cleavage. A completely different mutation pattern was observed when the mutant virus was passaged in mouse brains. The "pr" part of protein prM, which is removed by cleavage, contains six conserved Cys residues. The mutations selected in mice changed the number of Cys residues to five or seven by substitution mutations near the original cleavage site, probably causing a major perturbation of the structural integrity of protein prM. Although viable in mice, such Cys mutants could not be passaged in BHK-21 cells under normal growth conditions (37 degrees C), but one of the mutants exhibited a low level of infectivity at a reduced incubation temperature (28 degrees C). No evidence for the cleavage of protein prM in BHK-21 cells was obtained. This suggests that under certain growth conditions, the structural perturbation of protein prM can restore the infectivity of TBEV by circumventing the need for intracellular furin-mediated cleavage. This is the first example of a flavivirus using such a molecular mechanism.

Serine proteases regulating synaptic plasticity

A number of molecules have been postulated to be involved in long-term potentiation, an experimental model for learning and short-term memory. Although the molecular mechanisms of the long-term potentiation have been considerably well understood, it is not yet known why and how real memory can last very long with outstanding stability. A mechanical change of synaptic morphology at acquisition, consolidation and retention of memory is hypothesized to explain long-lasting memory. Changes in the synaptic morphology may be due, at least in part, to local extracellular proteolysis of cell adhesion and extracellular matrix molecules. Some extracellular serine proteases of the Clan PA family may modulate synaptic adhesion and associate with long-term potentiation and learning behavior. In the present review, candidate proteases that are involved in the hippocampal memory are overviewed.

The orphan granzymes of humans and mice

The granzyme/perforin pathway is a central pathway for lymphocyte-mediated killing in both the innate and adaptive immune systems. This pathway is important in a variety of host defenses, including viral clearance and tumor cell killing, and its dysregulation results in several human and rodent diseases. To date, the majority of reports in this field have concentrated on the functions of granzymes A and B. Recent reports, however, suggest that the non-A/non-B 'orphan' granzymes found in both humans and mice are potentially significant. Although the functions of these orphan granzymes have yet to be fully established, initial data suggests their importance in both immune and nonimmune cells.

The 2.2-A crystal structure of human pro-granzyme K reveals a rigid zymogen with unusual features

Granzyme K (GzmK) belongs to a family of trypsin-like serine proteases localized in electron dense cytoplasmic granules of activated natural killer and cytotoxic T-cells. Like the related granzymes A and B, GzmK can trigger DNA fragmentation and is involved in apoptosis. We expressed the Ser(195) --> Ala variant of human pro-GzmK in Escherichia coli, crystallized it, and determined its 2.2-A x-ray crystal structure. Pro-GzmK possesses a surprisingly rigid structure, which is most similar to activated serine proteases, in particular complement factor D, and not their proforms. The N-terminal peptide Met(14)-Ile(17) projects freely into solution and can be readily approached by cathepsin C, the natural convertase of pro-granzymes. The pre-shaped S1 pocket is occupied by the ion paired residues Lys(188B)-Asp(194) and is hence not available for proper substrate binding. The Ser(214)-Cys(220) segment, which normally provides a template for substrate binding, bulges out of the active site and is distorted. With analogy to complement factor D, we suggest that this strand will maintain its non-productive conformation in mature GzmK, mainly due to the unusual residues Gly(215), Glu(219), and Val(94). We hypothesize that GzmK is proteolytically active only toward specific, as yet unidentified substrates, which upon approach transiently induce a functional active-site conformation.

Decreased cerebrospinal fluid levels of neurosin (KLK6), an aging-related protease, as a possible new risk factor for Alzheimer's disease

Neurosin is a kallikrein-like serine protease expressed preferentially in the human brain. It is localized in senile plaques and neurofibrillary tangles in the brains of individuals with Alzheimer's disease (AD) and in Lewy bodies in patients with Parkinson's disease. Neurosin is present in the cerebrospinal fluid (CSF) as a proenzyme and does not show any enzymatic activity. We have developed a sandwich ELISA system using monoclonal and polyclonal antibodies against human neurosin and have measured neurosin levels in the CSF from AD and non-CNS disease patients. Both male and female patients with peripheral neuropathy showed statistically positive correlations between CSF neurosin concentrations and age (males, n = 52, r = 0.482, p < 0.005; females, n = 43, r = 0.365, p < 0.005). In contrast, such positive correlation was not observed in the CSF from patients with AD. Further, some such patients showed extremely low levels of CSF neurosin. Our results suggest that neurosin is an aging-related protease and that a decreased CSF concentration of neurosin may be a risk factor for developing AD.

cDNA cloning and tissue-specific splicing variants of mouse hippostasin/TLSP (PRSS20)

Two splicing variants of mouse hippostasin/TLSP (PRSS20) were identified and termed brain-type and prostate-type, respectively. Mouse hippostasin/TLSP showed 76.8% identity to the human homologue. Transient expression showed that both translational products were secreted into the conditioned medium. Mouse hippostasin/TLSP was expressed preferentially in the fetal brain and the prostate, but not in the neonatal brain. The brain expressed only brain-type hippostasin/TLSP, while the prostate expressed both types.

A novel isoform of a kallikrein-like protease, TLSP/hippostasin, (PRSS20), is expressed in the human brain and prostate

cDNAs encoding two splicing variants of a serine protease, termed hippostasin, were isolated by a PCR-based cloning strategy. The difference of 5' nucleotide sequence resulted in the variation in the amino terminal ends of the two, brain and prostate, types of human hippostasin. The longest ORF of the brain-type was 250 amino acids with a putative signal peptide, while that of the prostate-type was 282 amino acids. Homology search using the amino acid sequence revealed that prostate-type hippostasin was identical to TLSP (PRSS20), which is expressed in human primary keratinocytes (1). Transient expression analysis showed that both brain- and prostate-type TLSP/hippostasin were secreted into the conditioned medium as about 40 kDa proteins. Human TLSP/hippostasin showed 47% and 45% identity to trypsinogen II and kallikrein, respectively. In fact, the recombinant human TLSP/hippostasin efficiently cleaved Bz-Phe-Arg-4-methylcoumaryl-7-amide, a kallikrein substrate, and weakly cleaved other substrates for kallikrein and trypsin. Northern blot analysis detected a 1.3 kb band in the whole brain and a 1.4 kb band in the prostate and the lung. In situ hybridization revealed that it was expressed preferentially by the pyramidal neurons in the human hippocampus and secretory epithelial cells in the prostate. These results indicated that TLSP/hippostasin is involved in the functions of the human central nervous system and prostate and that it is a multifunctional protease present in various organs.