Expression mapping of cytotoxic T-lymphocyte antigen-2alpha gene transcripts in mouse brain

Cathepsin L coexists with Cytotoxic T-lymphocyte Antigen-2 alpha in distinct regions of the mouse brain

Cathepsins B and L are two prominent members of cystein proteases with broad substrate specificity and are known to be involved in the process of intra- and extra-cellular protein degradation and turnover. The propeptide region of cathepsin L is identical to Cytotoxic T-lymphocyte antigen-2α (CTLA-2α) discovered in mouse activated T-cells and mast cells. CTLA-2α exhibits selective inhibitory activities against papain and cathepsin L. We previously demonstrated the distribution pattern of the CTLA-2α protein in mouse brain by immunohistochemistry, describing that it is preferentially localized within nerve fibre bundles than neuronal cell bodies. In the present study we report colocalization of cathepsin L and CTLA-2α by double labeling immunofluorescence analysis in the mouse brain. In the telencephalon, immunoreactivity was identified in cerebral cortex and subcortical structures, hippocampus and amygdala. Within the diencephalon intense colocalization was detected in stria medullaris of thalamus, mammillothalamic tract, medial habenular nucleus and choroid plexus. Colocalization signals in the mesencephalon were strong in the hypothalamus within supramammillary nucleus and lateroanterior hypothalamic nucleus while in the cerebellum was in the deep white matter, granule cell layer and Purkinje neurons but moderately in stellate, and basket cells of cerebellar cortex. The distribution pattern indicates that the fine equilibrium between synthesis and secretion of cathespin L and CTLA-2α is part of the brain processes to maintain normal growth and development. The functional implication of cathespin L coexistence with CTLA-2α in relation to learning, memory and disease mechanisms is discussed.

Propeptides as modulators of functional activity of proteases

Most proteases are synthesized in the cell as precursor-containing propeptides. These structural elements can determine the folding of the cognate protein, function as an inhibitor/activator peptide, mediate enzyme sorting, and mediate the protease interaction with other molecules and supramolecular structures. The data presented in this review demonstrate modulatory activity of propeptides irrespective of the specific mechanism of action. Changes in propeptide structure, sometimes minor, can crucially alter protein function in the living organism. Modulatory activity coupled with high variation allows us to consider propeptides as specific evolutionary modules that can transform biological properties of proteases without significant changes in the highly conserved catalytic domains. As the considered properties of propeptides are not unique to proteases, propeptide-mediated evolution seems to be a universal biological mechanism.

Identification and characterization of the interactive proteins with cytotoxic T-lymphocyte antigen-2α

Cytotoxic T-lymphocyte antigen-2α (CTLA-2α) is a potent inhibitor of cathepsin L-like cysteine proteases. Recombinant CTLA-2α is known to be a potent, competitive inhibitor of cathepsin L-like cysteine proteases. In this study, cathepsin L, cathepsin C, and tubulointerstitial nephritis antigen-related protein 1 (TINAGL1) were identified as novel interactive proteins of CTLA-2α by the yeast two-hybrid screening system. The direct interactions and co-localization of these proteins with CTLA-2α were confirmed using co-immunoprecipitation and immunofluorescence staining, respectively. The disulfide-bonded CTLA-2α/cathepsin L complex was isolated from mouse tissue. CTLA-2α was found to be specific and consistently expressed on the maternal side of the mouse placenta. Double immunofluorescence analysis showed that CTLA-2α was co-localized with cathepsin L, cathepsin C, and TINAGL1 in placenta. A simple cell-based fluorescence assay revealed that CTLA-2α exhibited inhibitory activity toward cathepsin C in live cells, which indicated that CTLA-2α is a novel endogenous inhibitor of cathepsin C.

Studies of inhibitory mechanisms of propeptide-like cysteine protease inhibitors

Mouse cytotoxic T-lymphocyte antigen-2α (CTLA-2α), Drosophila CTLA-2-like protein (crammer), and Bombyx cysteine protease inhibitor (BCPI) belong to a novel family of cysteine protease inhibitors (I29). Their inhibitory mechanisms were studied comparatively. CTLA-2α contains a cysteine residue (C75), which is essential for its inhibitory potency. The CTLA-2α monomer was converted to a disulfide-bonded dimer in vitro and in vivo. The dimer was fully inhibitory, but the monomer, which possessed a free thiol residue, was not. A disulfide-bonded CTLA-2α/cathepsin L complex was isolated, and a cathepsin L subunit with a molecular weight of 24,000 was identified as the interactive enzyme protein. Crammer also contains a cysteine residue (C72). Both dimeric and monomeric forms of crammer were inhibitory. A crammer mutant with Cys72 to alanine (C72A) was fully inhibitory, while the replacement of Gly73 with alanine (G73A) caused a significant loss in inhibitory potency, which suggests a different inhibition mechanism from CTLA-2α. BCPI does not contain cysteine residue. C-terminal region (L77-R80) of BCPI was essential for its inhibitory potency. CTLA-2α was inhibitory in the acidic pH condition but stabilized cathepsin L under neutral pH conditions. The different inhibition mechanisms and functional considerations of these inhibitors are discussed.

Cytotoxic T lymphocyte antigen-2 alpha induces apoptosis of murine T-lymphoma cells and cardiac fibroblasts and is regulated by cAMP/PKA

The mechanism of cAMP-promoted apoptosis is not well defined. In wild-type (WT) murine S49 lymphoma cells, cAMP promotes apoptosis in a protein kinase A (PKA)-dependent manner. We find that treatment of WT S49 cells with 8-CPT-cAMP prominently increases the expression (as determined by DNA microarray analysis, real-time PCR and immunblotting) of cytotoxic T lymphocyte antigen-2α (CTLA-2α), a cathepsin L-like cysteine protease inhibitor. By contrast, CTLA-2α expression is only slightly increased by 8-CPT-cAMP treatment of D-S49 cells, which lack cAMP/PKA-promoted apoptosis. Raising endogenous cAMP (by use of forskolin or inhibition of phosphodiesterase [PDE] 4) or a PKA-selective, but not an Epac-selective, cAMP analogue, increases CTLA-2α mRNA expression; PKA, and not Epac, thus mediates the increase in CTLA-2α expression. An adenoviral CLTA-2α (Ad-CTLA-2α) construct induces apoptosis and enhances cAMP-promoted apoptosis in WT S49 cells but such cells do not have an increase in cathepsin L activity nor does a cathepsin L inhibitor alter cAMP-promoted apoptosis. 8-CPT-cAMP also increases CTLA-2α expression and induces apoptosis in murine cardiac fibroblasts; knockdown of CTLA-2α expression by siRNA blocks 8-CPT-cAMP-promoted apoptosis. Thus, cAMP increases CTLA-2α expression in murine lymphoma and cardiac fibroblasts and this increase in CTLA-2α contributes to cAMP/PKA-promoted apoptosis by mechanisms that are independent of the ability of CTLA-2α to inhibit cathepsin L.

Changes of gene expression profiles in the cervical spinal cord by acupuncture in an MPTP-intoxicated mouse model: microarray analysis

It has been shown that acupuncture at acupoints GB34 and LR3 inhibits the degeneration of nigrostriatal neurons in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. The degeneration of spinal cord was reported to be induced in the MPTP-treated pre-symptomatic mouse. In this study, the gene expression profile changes following acupuncture at the acupoints were investigated in the cervical spinal cord of an MPTP-induced parkinsonism model using a whole transcript array (Affymetrix GeneChip mouse gene 1.0 ST array). It was shown that 8 of the probes up-regulated in MPTP, as compared to the control, were down-regulated after acupuncture at the acupoints. Of these 8 probes, 6 probes (4 annotated genes in 6 probes: Ctla2a, EG383229, Ppbp and Ube2l6) were exclusively down-regulated by acupuncture at the specific acupoints except for 2 probes as these 2 probes were commonly down-regulated by acupuncture at both the acupoints and the non-acupoints. In addition, 11 of the probes down-regulated in MPTP, as compared to the control, were up-regulated by acupuncture at the acupoints. Of these 11 probes, 10 probes (5 annotated genes in 10 probes: EG665033, ENSMUSG00000055323, Obox6, Pbp2 and Tmem150) were exclusively up-regulated by acupuncture at the specific acupoints except for the Fut11 because the Fut11 was commonly up-regulated by acupuncture at both the acupoints and the non-acupoints. The expression levels of the representative genes in the microarray were validated by real-time RT-PCR. These data suggest that the expression of these exclusively regulated 16 probes (9 genes) may be, at least in part, affected by acupuncture at the acupoints in the cervical spinal cord which can be damaged by MPTP intoxication.

Identification of essential residues of CTLA-2alpha for inhibitory potency

To identify functionally essential sequences and residues of CTLA-2alpha, in vitro mutagenesis was carried out. The coefficient of inhibition (K(i)) was determined towards rabbit cathepsin L using Z-Phe-Arg-MCA as the substrate. Recombinant CTLA-2alpha inhibited the enzyme potently (K(i) = 15 nM). A truncated mutant, lacking the N- and C-terminal Ala1-Asp9 and Leu80-Glu109 regions, was also a potent inhibitor (K(i) = 10 nM). Subsequent short deletions in the central region (Asn10-Ser79) showed three functionally essential distinct regions: Asn10-Phe19, His30-Ala44 and Ser55-Ser79. These regions cover sequences corresponding to three helices (alpha1, alpha2 and alpha3) and sequences that interact with the cognate enzyme. Alanine scanning showed that replacement of one of three conserved Trp residues increased the K(i) by 15-20-fold; whereas, replacement of two/three Trp residues at once caused complete loss of potency, as did replacing Cys75 with Ala or Ser. The proteins from wild-type (WT) CTLA-2alpha and mutant C75A were stable overnight when incubated with cathepsin L; whereas, proteins from mutants W12A, W15A and W35A were quickly digested. Incubation of cathepsin L/WT CTLA-2alpha formed a complex; whereas, C75S did not form a complex. Our overall results point to a critical role of W12, W15, W35 and Cys75 residues in CTLA-2alpha.

Dendritic and axonal localization of cytotoxic T-lymphocyte antigen-2 alpha protein in mouse brain

Cytotoxic T-lymphocyte antigen-2 alpha (CTLA-2alpha) is a novel cysteine proteinase inhibitor protein originally discovered and expressed in mouse activated T-cells and mast cells. Expressed recombinant CTLA-2alpha is shown to exhibit selective inhibition of cathepsin L-like cysteine proteinases. We have recently reported the expression pattern of CTLA-2alpha mRNA in mouse brain by in situ hybridization, demonstrating that it is mainly enriched within neuronal populations. In this study we present the distribution profile of the protein by immunohistochemical analysis. Results showed that CTLA-2alpha protein is preferentially localized in dendritic and axonal compartments. In telencephalon, strong labeling was detected in dendrites in the cerebral cortices, stratum radiatum and stratum lacunosum moleculare and within axonal fibers of stratum lucidum where mossy fibers emanating from all parts of the granule cell layer of dentate gyrus terminate at pyramidal neurons and interneurons. In diencephalon, moderate staining was found in all thalamic nuclei but was strong in medial habenular nucleus and the hypothalamic nuclei including suprachiasmatic nucleus, optic chiasm, arcuate nucleus and median eminence. In mesencephalon, strong immunoreactivity was detected in superior colliculus, inferior colliculus and paramedian raphe nucleus. In the rhombencephalon, the pontine nucleus and transverse fibers of the pons revealed strong staining but were moderate in vestibular nuclei. Strong immunoreactivity was also observed in the internal white matter, granule cell layer and Purkinje cell layer within cerebellum. On Western blot analysis, a band of 14 kDa for CTLA-2alpha from protein extracts of the cerebrum, cerebellum, pons and medulla was detected. The distribution pattern and functional considerations of CTLA-2alpha in the brain are discussed.

Recent progress in histochemistry

The progress in discerning the structure and function of cells and tissues in health and disease has been achieved to a large extent by the continued development of new reagents for histochemistry, the improvement of existing techniques and new imaging techniques. This review will highlight some advancements made in these fields.