Celastrol inhibits the proliferation and induces apoptosis of colorectal cancer cells via downregulating NF-κB/COX-2 signaling pathways

BACKGROUND

Colorectal cancer (CRC) is the third-ranked malignant tumor in the world that contributes to the death of a major population of the world. Celastrol, a bioactive natural product isolated from the medicinal plant Tripterygium wilfordii Hook F, has been proved to be an effective anti-tumor inhibitor for multiple tumors.

OBJECTIVE

To reveal the therapeutic effect and underlying mechanisms of celastrol on CRC cells.

METHODS

CCK-8 and clonogenic assay were used to analyze the cell proliferation in CRC cells. Flow cytometry analysis was conducted to assess the cell cycle and cell apoptosis. Wound-healing and cell invasion assay were used to evaluate the migrating and invasion capability of CRC cells. The potential antitumor mechanism of celastrol was investigated by qPCR, western blot, and confocal immunofluorescence analyses.

RESULTS

Celastrol effectively inhibited CRC cell proliferation by activating caspase-dependent cell apoptosis and facilitating G1 cell cycle arrest in a dose-dependent manner, as well as cell migration and invasion by downregulating the MMP2 and MMP9. Mechanistic protein expression revealed that celastrol suppressed the expression of COX-2 by inhibiting the phosphorylation of NF-κB p65 and subsequently leading to cytoplasmic retention of p65 protein, thereby inhibiting its nuclear translocation and transcription activities.

CONCLUSION

These findings indicate that celastrol is an effective inhibitor for CRC, regulating the NF-κB/COX-2 pathway, leading to the inhibition of cell proliferation characterized by cell cycle arrest and caspase-dependent apoptosis, providing a potential alternative therapeutic agent for CRC patients.

Up‑regulation of lncRNA PXN-AS1-L is associated with unfavorable prognosis in patients suffering from glioma

OBJECTIVE

Growing evidence has proved that long noncoding RNAs (lncRNAs) act as novel regulators in the progression of various tumors by modulating miRNAs and tumor-related genes. However, the potential function of lncRNA PXN-AS1-L (PXN-AS1-L) in glioma remains unknown. Hence, we aimed to determine whether PXN-AS1-L was dysregulated in glioma and further preliminarily explored its prognostic value in glioma patients.

PATIENTS AND METHODS

RT-PCR was used for the assessment of PXN-AS1-L levels in glioma tissue and matched normal tissues from our hospital. Chi-square test was applied to explore the possible association between PXN-AS1-L expressions and clinical factors. Kaplan-Meier survival analysis was carried out to determine the influence of PXN-AS1-L expressions on the survival rate of glioma patients. Survival data were further evaluated through univariate and multivariate analyses.

RESULTS

PXN-AS1-L levels were differentially upregulated in glioma specimens compared with paired non-tumor specimens. Higher levels of PXN-AS1-L in glioma were observed to be positively associated with WHO grade (p = 0.019), KPS (p = 0.008)and tumor recurrence (p = 0.019). Survival assays revealed that glioma patients with higher PXN-AS1-L expressions had worse overall survival rates. In multivariate analysis, upregulation of PXN-AS1-L expressions (Risk ratio = 2.663, 1.218-4.532, p = 0.014) in glioma tissues was confirmed to be an independent prognostic factor of overall survival in patients.

CONCLUSIONS

We firstly suggested that PXN-AS1-L was overexpressed in glioma, and could be used as a novel marker of unfavorable outcome in glioma patients.

Over-expression of DJ-1 attenuates effects of curcumin on colorectal cancer cell proliferation and apoptosis

OBJECTIVE

The phosphatase and tensin homologue deleted on chromosome ten (PTEN) acts as a tumor suppressor gene by inhibiting the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway. DJ-1, a negative regulator of PTEN, is associated with the pathogenesis of a variety of tumors. Curcumin (Cur) is a phenolic compound that is extracted from various plant rhizomes with various anti-tumor pharmacological effects. This study aimed to investigate the effects of Cur on proliferation and apoptosis of colorectal cancer cells.

MATERIALS AND METHODS

Human normal colorectal epithelial cell line (NCM460) and colorectal cancer cell line (SW480 and SW620) were cultured in vitro. Real-time quantitative PCR (RT-PCR) and western blot were used to detect DJ-1 and PTEN mRNA and protein, respectively. Cell apoptosis was determined with flow cytometry. SW480 cells were divided into control, 20 μM Cur treatment group, Cur+pcDNA3.1-Blank group and Cur+pcDNA3.1-DJ-1 group. Cell proliferation activity was evaluated with EdU staining.

RESULTS

Comparing with NCM460 cells, DJ-1 was significantly increased, while PTEN was significantly declined in SW480 and SW620 cells (p<0.05). Cur treatment significantly inhibited SW480 and SW620 cell proliferation and significantly induced apoptosis compared to control group (p<0.05) but showed no significant effects on NCM460 cells. Cur down-regulated DJ-1 level and enhanced PTEN expressions in SW480 cells with dose dependence. The pcDNA3.1-DJ-1 transfection significantly declined PTEN expression, enhanced p-AKT levels, reduced cell apoptosis, and strengthened cell proliferation in SW480 cells treated by Cur (p<0.05).

CONCLUSIONS

Cur can inhibit colorectal cancer cell proliferation and promote apoptosis by down-regulating DJ-1 expression to regulate the activity of PTEN/PI3K/AKT signaling pathway.

Micheliolide suppresses the viability, migration and invasion of U251MG cells via the NF-κB signaling pathway

Micheliolide (MCL), a sesquiterpene lactone isolated from Michelia compressa and Michelia champaca, has been used previously to inhibit the NF-κB signaling pathway. MCL has exerted various therapeutic effects in numerous types of disease, such as inflammatory and cancer. However, to the best of our knowledge, its underlying anticancer mechanism remains to be understood. The present study aimed to investigate the effects of MCL on human glioma U251MG cells and to determine the potential anticancer mechanism of action of MCL. From Cell Counting Kit-8, colony formation assay, apoptosis assay and Confocal immunofluorescence imaging analysis, the results revealed that MCL significantly inhibited cell viability in vitro and induced cell apoptosis via activation of the cytochrome c/caspase-dependent apoptotic pathway. In addition, MCL also suppressed cell invasion and metastasis via the wound healing and Transwell invasion assays. Furthermore, western blot and reverse transcription PCR analyses demonstrated that MCL significantly downregulated cyclooxygenase-2 (COX-2) expression levels, which may have partially occurred through the inactivation of the NF-κB signaling pathway. In conclusion, the results of the present study indicated that MCL may inhibit glioma carcinoma growth by downregulating the NF-κB/COX-2 signaling pathway, which suggested that MCL may be a novel and alternative antitumor agent for the treatment of human glioma carcinoma.

Over-expression of DJ-1 attenuates effects of curcumin on colorectal cancer cell proliferation and apoptosis

Since this article has been suspected of research misconduct and the corresponding authors did not respond to our request to prove originality of data and figures, "Over-expression of DJ-1 attenuates effects of curcumin on colorectal cancer cell proliferation and apoptosis, by H. Shang, T. Wang, F. Shang, M. Li, Y. Luo, K.-M. Huang, published in Eur Rev Med Pharmacol Sci 2019; 23 (7): 3080-3087-DOI: 10.26355/eurrev_201904_17591-PMID: 31002157" has been withdrawn. The Publisher apologizes for any inconvenience this may cause. https://www.europeanreview.org/article/17591.

Increased HSPG2 expression independently predicts poor survival in patients with oligoastrocytoma and oligodendroglioma

OBJECTIVE

Perlecan, which is also called heparan sulfate proteoglycan 2 (HSPG2), is a protein encoded by the HSPG2 gene that maps to 1p36.12 in the human genome. In this study, we assessed the independent prognostic value of HSPG2 in terms of overall survival (OS) and recurrence-free survival (RFS) in patients with LGG.

PATIENTS AND METHODS

A retrospective study was conducted by using data in the Cancer Genome Atlas-Low Grade Glioma (TCGA-LGG).

RESULTS

Increased HSPG2 expression was an independent prognostic indicator of poor OS in oligoastrocytoma (HR: 1.644, 95% CI: 1.116-2.423, p = 0.012) and in oligodendroglioma (HR: 1.459, 95% CI: 1.138-1.871, p = 0.003). In addition, increased HSPG2 expression independently predicted poor RFS in oligodendroglioma (HR: 1.402, 95% CI: 1.110-1.770, p = 0.005). Furthermore, we observed that high HSPG2 expression was associated with significantly shorter OS and RFS in oligodendroglioma, no matter the patients received radiotherapy or not. Using copy number alterations (CNAs) and DNA methylation data in TCGA-LGG, we found that DNA copy deletion was generally associated with decreased HSPG2 expression. Regression analysis suggested a weak negative correlation between HSPG2 expression and HSPG2 DNA methylation (Pearson's r = -0.388).

CONCLUSIONS

Increased HSPG2 expression could independently predict poor OS in oligoastrocytoma and oligodendroglioma and also independently predicted poor RFS in oligodendroglioma. Its expression is modulated by both DNA copy number and DNA methylation in oligodendroglioma.

Tudor knockdown disrupts ovary development in Bactrocera dorsalis

One of the main functions of the piwi-interacting RNA pathway is the post-transcriptional silencing of transposable elements in the germline of many species. In insects, proteins belonging to the Tudor superfamily proteins belonging to the Tudor superfamily play an important role in to play an important role in this mechanism. In this study, we identified the tudor gene in the oriental fruit fly, Bactrocera dorsalis, investigated the spatiotemporal expressional profile of the gene, and performed a functional analysis using RNA interference. We identified one transcript for a tudor homologue in the B. dorsalis transcriptome, which encodes a protein containing the typical 10 Tudor domains and an Adenosine triphosphate (ATP) synthase delta subunit signature. Phylogenetic analysis confirmed the identity of this transcript as a tudor homologue in this species. The expression profile indicated a much higher expression in the adult and pupal stages compared to the larval stages (up to a 60-fold increase), and that the gene was mostly expressed in the ovaries, Malpighian tubules and fat body. Finally, gene knockdown of tudor in B. dorsalis led to clearly underdeveloped ovaries in the female adult and reductions in copulation rate and amount of oviposition, indicating its important role in reproduction. The results of this study shed more light on the role of tudor in ovary development and reproduction.

Glutathiolation Triggers Proteins for Degradation by the Ubiquitin- Proteasome Pathway

BACKGROUND

Glutathione is a small antioxidant peptide in cells and it plays an important role in maintaining a reducing intracellular environment. Glutathione is also involved in the dynamic regulation of specific protein functions by reversible glutathiolation of certain proteins in response to oxidative stress.

OBJECTIVE

The purpose of this work is to mechanistically investigate the effects of glutathiolation on the susceptibility of proteins to degradation by the ubiquitinproteasome pathway (UPP).

METHODS AND RESULTS

The data show that γC-crystallin and carbonic anhydrase III were barely degraded by the UPP without modifications, but both were rapidly degraded by the UPP after glutathiolation. Modifications of sulfhydryls by other thiol-modification reagents, such as iodoacetamide, also increased the degradation of γC-crystallin, but not as effectively as glutathiolation. Biophysical analysis showed that glutathiolation caused reversible conformational changes of these proteins, including a significant increase in protein surface hydrophobicity and a decrease in thermal stability. The modified protein regained its native conformation and its resistance to degradation upon removal of the glutathione moiety. A cataract-causing T5P mutant γC-crystallin shares many biophysical characteristics as glutathiolated γC-crystallin, including increased surface hydrophobicity and decreased thermal stability. T5P mutant γC-crystallin was also rapidly degraded. Comparison of the conformational changes and the susceptibility to degradation of glutathiolated γC-crystallin with other forms of modified γC-crystallin suggests that the glutathiolation-induced exposure of hydrophobic patches, rather than the modification per se, serves as the signal for degradation by the UPP. Consistent with this hypothesis, masking the surface hydrophobicity of glutathiolated and T5P mutant γC-crystallins significantly reduced their susceptibility to degradation by the UPP.

CONCLUSION

This work demonstrates that glutathiolation is a novel mechanism for the UPP to recognize substrates in response to oxidative stress.

The Fate of In Situ Lens Regeneration is Determined by Capsulorhexis Size

BACKGROUND AND OBJECTIVE

Lens regeneration is an optimal strategy for cataract patients to regain visual acuity with accommodation. We recently designed a novel, minimally invasive capsulorhexis surgical method for cataract removal that achieved functional lens regeneration in human infants. However, small anterior capsulorhexis requires advanced surgical expertise. To examine whether the quality of the regenerated lens can be maintained with enlarged anterior capsulorhexis, we investigated the shape and transparency of the regenerated lenses with different anterior capsulorhexis diameters (ACDs).

METHODS

Thirty-six 4-week-old New Zealand albino rabbits were randomly divided into three groups which underwent lens extraction with different ACDs (Group A: 2.0±0.5 mm, Group B: 4.0±0.5 mm, Group C: 6.0±0.5 mm). The anterior capsule opening area (ACOA) was quantified, and the morphology, weight, and histological characteristics of the regenerated lenses were examined.

RESULTS

Lens regeneration was observed in all three groups. In Group A, the regenerated lenses were relatively complete and transparent. In Groups B and C, the regenerated lenses were doughnut-shaped and opaque. The speed of lens regeneration in Group A was significantly faster than that in Groups B and C. The ACOA in Group A healed quickly and completely approximately 2 weeks after surgery. However, in Groups B and C, ACOA did not heal completely until 12 weeks after surgery. Histological examination showed that in Group A, most of the lens epithelial cells differentiated into well-organized lens fibers. However, in Groups B and C, the regenerated lens fibers were disorganized.

CONCLUSION

Capsulorhexis size is a critical determinant of integrity and transparency in lens regeneration.

Proteotoxic Stress Desensitizes TGF-beta Signaling Through Receptor Downregulation in Retinal Pigment Epithelial Cells

Background:

Proteotoxic stress and transforming growth factor (TGFβ)-induced epithelial-mesenchymal transition (EMT) are two main contributors of intraocular fibrotic disorders, including proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR). However, how these two factors communicate with each other is not well-characterized.

Objective:

The aim was to investigate the regulatory role of proteotoxic stress on TGFβ signaling in retinal pigment epithelium.

Methods:

ARPE-19 cells and primary human retinal pigment epithelial (RPE) cells were treated with proteasome inhibitor MG132 and TGFβ. Cell proliferation was analyzed by CCK-8 assay. The levels of mesenchymal markers α-SMA, fibronectin, and vimentin were analyzed by real-time polymerase chain reaction (PCR), western blot, and immunofluorescence. Cell migration was analyzed by scratch wound assay. The levels of p-Smad2, total Smad2, p-extracellular signal-regulated kinase 1/2 (ERK1/2), total ERK1/2, p-focal adhesion kinase (FAK), and total FAK were analyzed by western blot. The mRNA and protein levels of TGFβ receptor-II (TGFβR-II) were measured by real-time PCR and western blot, respectively.

Results:

MG132-induced proteotoxic stress resulted in reduced cell proliferation. MG132 significantly suppressed TGFβ-induced upregulation of α-SMA, fibronectin, and vimentin, as well as TGFβ-induced cell migration. The phosphorylation levels of Smad2, ERK1/2, and FAK were also suppressed by MG132. Additionally, the mRNA level and protein level of TGFβR-II decreased upon MG132 treatment.

Conclusion:

Proteotoxic stress suppressed TGFβ-induced EMT through downregulation of TGFβR-II and subsequent blockade of Smad2, ERK1/2, and FAK activation.

Vitellogenin and its receptor play essential roles in the development and reproduction of the brown citrus aphid, Aphis (Toxoptera) citricidus

Vitellogenin (Vg) and its receptor (VgR) play a key role in the reproductive process and development of insects. Aphids are a group of high-fecundity insect species with pseudoplacental viviparity, but the roles of their Vg and VgR genes have not been investigated yet. The brown citrus aphid, Aphis (Toxoptera) citricidus, is a major insect pest of citrus and the main vector of Citrus tristeza closterovirus. In this study, we identified and characterized these two genes, designated as AcVg and AcVgR, from the brown citrus aphid. We found that AcVg has lost the DUF1943 domain that is present in other insect Vgs. Silencing of AcVg and AcVgR led to a delay in the nymph-adult transition, a prolonged prereproductive period, and a shortened reproductive period, which in turn resulted in slower embryonic development and fewer new-born nymphs. Interestingly, silencing of AcVg decreased the transcript level of AcVgR, but silencing of AcVgR resulted in increased transcript levels of AcVg. In addition, silencing of Vg/VgR had similar phenotypes between alate and apterous morphs, suggesting that the functions of these two genes are the same in the two wing morphs of the aphid. Our results demonstrate that Vg and VgR are involved in various aspects of aphid development and reproduction. Further studies on the synthesis of Vg could help to elucidate the reproductive mechanism and provide information that will be useful for developing new pest control strategies.

Long non-coding RNA TUSC7 expression is independently predictive of outcome in glioma

OBJECTIVE

Down-regulation of long non-coding RNA tumor suppressor candidate 7(TUSC7) contributes to tumorigenesis in several human cancers including glioma. However, the prognostic value of TUSC7 in glioma remains unclear. The present study aimed to investigate the clinicopathological and prognostic value of TUSC7.

PATIENTS AND METHODS

The expression level of TUSC7 in glioma tissues and matched normal tissues were detected by qRT-PCR. Then, the association of serum TUSC7 expression level with various important clinicopathological parameters and survival rates was evaluated. The Cox regression analysis was used to evaluate the effect of independent prognostic factors on survival outcome.

RESULTS

The relative level of TUSC7 was significantly lower in glioma tissues compared to the adjacent normal brain tissues (p < 0.01). In addition, a lower expression of TUSC7 was observed in high-grade glioma tissues than in low-grade glioma tissues (p < 0.01). Furthermore, the low expression of TUSC7 was associated with poor clinicopathological characteristics of glioma, including WHO grade (p = 0.002) and KPS (p = 0.026). Then, the low TUSC7 level was correlated with shorter disease free survival (DFS) and overall survival (OS) than low level (both p = 0.05). Finally, univariate and multivariate Cox analysis showed that TUSC7 was an independent prognostic indicator for OS and DFS.

CONCLUSIONS

These results provided evidence that TUSC7 may be a potential biomarker in the prognosis of glioma.

Identification, characterization and functional analysis of a chitin synthase gene in the brown citrus aphid, Toxoptera citricida (Hemiptera, Aphididae)

Chitin synthase (CHS) is a crucial enzyme involved in the final step of the insect chitin biosynthetic pathway. In this study, we cloned the full-length cDNA sequence of a chitin synthase gene (TCiCHS) from the brown citrus aphid, Toxoptera citricida, an important citrus pest and the main vector of citrus tristeza virus worldwide. TCiCHS was expressed during the entire lifecycle and in all insect tissues examined. Expression was highest in first-second-instar nymphs, nymph-adult transitions and in the abdomen (6.7-fold higher than head). Embryos had a higher expression level than the integument. Fourth-instar nymphs were exposed to 5 and 500 mg/l concentrations of the chitin synthesis inhibitor diflubenzuron (DFB) for 48 h and had the highest mortality at the 500 mg/l concentration. The mRNA expression levels of TCiCHS were significantly enhanced upon the exposure of nymphs to both low and high DFB concentrations. Silencing of TCiCHS occurred through plant-mediated double-stranded RNA (dsRNA) feeding. Most dsRNA-fed nymphs were unable to moult to the next stage, and the expression of TCiCHS decreased 48% compared with controls. These results demonstrate that TCiCHS plays an important role in nymph to adult development, is possibly help identify molecular targets for To. citricida control.

CHIP Knockdown Reduced Heat Shock Response and Protein Quality Control Capacity in Lens Epithelial Cells

Protein quality control (PQC) systems, including molecular chaperones and ubiquitin-proteasome pathway (UPP), plays an important role in maintaining intracellular protein homeostasis. Carboxyl terminus of Hsc70- interacting protein (CHIP) links the chaperone and UPPs, thus contributing to the repair or removal of damaged proteins. Over-expression of CHIP had previously been used to protect cells from environmental stress. In order to gain a more physiologic mechanism of the advantage conferred by CHIP, we induced a CHIP knockdown and monitored the ability of cells to cope with environmental stress. To knockdown CHIP, the human lens epithelial cell line HLE B3 was transfected with lentiviral particles that encode a CHIP short hairpin RNA (shRNA) or negative control lentiviral particles. Stable CHIP-knock down cells (KD) and negative control cells (NC) were selected with puromycin. After exposure to heat shock stress, there was no change observed in the expression of Hsp90. In contrast, Hsp70 levels increased significantly in NC cells but less so in KD cells. Hsp27 levels also increased after heat shock, but only in NC cells. Protein ubiquitination was reduced when CHIP was knocked down. CHIP knockdown reduced the ability to clear aggregation proteins. When same levels of aggregation-prone RFP-mutant crystallin fusion protein, RFP/V76D-γD, was expressed, there was ~9- fold more aggregates in KD cells as compared to that observed in NC cells. Furthermore, KD cells were more sensitive to toxicity of amino acid analog canavanine as compared to NC cells. Together, these data indicate that CHIP is required for PQC and that CHIP knockdown diminished cellular PQC capacity in lens cells.

Release of ATP from rat urinary bladder mucosa: role of acid, vanilloids and stretch

BACKGROUND AND PURPOSE

ATP, released from urothelial cells, modulates afferent nerve firing from the urinary bladder. Here, we have characterized ATP release from the rat bladder mucosa in response to acid, capsaicin, electrical field stimulation (EFS) and stretch, using agonists and antagonists at transient receptor potential vanilloid receptor 1 (TRPV1) and acid-sensing ion channels (ASICs).

EXPERIMENTAL APPROACH

Rat mucosal strips (containing urothelium and lamina propria) in Perspex microbaths were superfused with Krebs solution. ATP was measured after exposure of matched strips to acid (pH 6.6-5.0), capsaicin (0.1-10 microM), EFS or stretch (150% of original length).

KEY RESULTS

Median basal ATP release was 3.46 nmol g(-1). The mucosal strips responded to stimuli with potency order (median, IQR): acid (pH 5.6-6.0) 286 (103-555) > 10 microM capsaicin 188 (117-431) > 10 Hz EFS 63.0 (13.3-96.4) > stretch 24.4 (6.73-55.1) nmol ATP g(-1). ATP release in response to acid was pH dependent (P < 0.05). Responses to capsaicin did not desensitize nor were they concentration dependent. TRPV1 antagonist, capsazepine (10 microM) abolished capsaicin-evoked ATP release, and reduced acid-evoked (pH 6.5) release to 30% (P < 0.001). The ASIC channel antagonists gadolinium (0.1 mM) and amiloride (0.3 microM) reduced (P < 0.05) the acid-evoked (pH 6.5) release to 40 and 6.5% respectively. ASIC (ASIC1, ASIC2a, ASIC2b, ASIC3) and two TRPV1 gene products were detected in mucosal and detrusor extracts.

CONCLUSIONS AND IMPLICATIONS

Capsaicin (at TRPV1) and acid (at both TRPV1 and ASIC) induce ATP release from the rat bladder mucosa. This ATP appears to be principally of urothelial origin. This study highlights the importance of ATP and acid as signalling molecules in modulating bladder function.

Expression of K6W-ubiquitin in lens epithelial cells leads to upregulation of a broad spectrum of molecular chaperones

PURPOSE

Accumulation and precipitation of abnormal proteins are associated with many age-related diseases. The ubiquitin-proteasome pathway (UPP) is one of the protein quality control mechanisms that selectively degrade damaged or obsolete proteins. The other arm of the protein quality control mechanism is molecular chaperones, which bind to and help refold unfolded or misfolded proteins. We previously showed that the molecular chaperones and the UPP work in a competitive manner in eliminating the denatured proteins. To further investigate the interaction between the two protein quality control mechanisms, we determined the effects of the impairment of the UPP on the expression of molecular chaperones in human lens epithelial cells (HLEC).

METHODS

K6W-ubiquitin, a dominant negative inhibitor of the UPP, was expressed in confluent HLEC via an adenoviral vector. The mRNA levels of cytoplasmic and endoplasmic reticulum (ER) chaperones were determined by real-time reverse transcription polymerase chain reaction (RT-PCR). Protein levels for these chaperones were determined by western blotting.

RESULTS

Expression of K6W-ubiquitin in HLEC increased the expression of a broad spectrum of molecular chaperones. Among the heat-shock proteins, mRNA for alphaB-crystallin, Hsp70, and Hsp90 increased 27 fold, 21 fold, and twofold, respectively, in response to K6W-ubiquitin expression. Among the ER chaperones and ER stress related factors, mRNA levels of protein disulfide isomerase, Grp75, Grp78, Grp94, and the CAAT/enhancer binding protein homologous protein (CHOP) increased from 1.7 fold to 3.7 fold. The mRNA for Hsp60 also increased 1.6 fold in response to the expression of K6W-ubiquitin. The expression pattern of these chaperones in response to the expression of K6W ubiquitin is similar to that obtained when cells were treated with proteasome inhibitors or heat-shock.

CONCLUSIONS

It appears that the upregulation of these chaperones is related to the elevated levels of abnormal proteins in the cells. These findings support our hypothesis that the molecular chaperones and the UPP may back each other up in the process of protein quality control. The upregulation of molecular chaperones in response to the expression of a dominant negative ubiquitin may compensate for the impairment of the UPP in the degradation of abnormal proteins.

Selectivity of the ubiquitin pathway for oxidatively modified proteins: relevance to protein precipitation diseases

There is now consensus that the accumulation of oxidatively modified proteins is cytotoxic and causally related to several age-related diseases, including the amyloid diseases and age-related cataracts. There is also general agreement that proteolytic pathways provide a quality control mechanism to limit accumulation of damaged proteins. Although many researchers assume that the ubiquitin pathway is involved in recognition and proteolytic removal of oxidatively modified proteins, which are produced upon cellular stress, there has been no direct evidence to support this hypothesis. In this work, we used a novel proteolysis-resistant ubiquitin variant to demonstrate that ubiquitin conjugates isolated from oxidatively stressed mammalian cells are enriched 3.3-15-fold for oxidatively modified proteins and that failure to execute ubiquitin-dependent proteolysis renders various cell types more susceptible to oxidative stress-related cytotoxicity. These results were corroborated using several inhibitors of the ubiquitin proteasome pathway, including PS-341, an anticancer drug in clinical use. Taken together the data indicate that the ubiquitin proteolytic pathway recognizes and removes oxidatively modified proteins, and that failure of this system, as occurs upon aging or stress, may be involved in and exacerbate cytotoxicity and age-related syndromes in which accumulation of ubiquitinated and oxidatively modified proteins has an etiologic role.

Ubiquitin-activating enzyme (E1) isoforms in lens epithelial cells: origin of translation, E2 specificity and cellular localization determined with novel site-specific antibodies

Lens development and response to peroxide stress are associated with dramatic changes in protein ubiquitination, reflecting dynamic changes in activity of the ubiquitin-activating enzyme (E1). Two isoforms of E1 (E1A and E1B) have been identified in lens cells although only one E1 mRNA, containing three potential translational start sites, has been detected. Novel, site-specific antibodies to E1 were generated and the hypothesis that the two isoforms of E1 are translated from alternative initiation codons of a single mRNA was tested. Antibodies raised against E1A-N peptide (Met(1)to Cys(23)of E1A) reacted only with E1A by immunoblot and immunoprecipitation. Antibodies raised against E1B-N peptide (Met(1)to Glu(25)of E1B or Met(41)to Glu(65)of E1A) and E1AB-C peptide (His(1030)to Arg(1058)of E1A or His(990)to Arg(1018)of E1B) reacted with both E1A and E1B. These results indicate that (1) E1A and E1B contain the same C-terminal residues; (2) E1A contains the N terminal sequence of E1B; and (3) E1B does not contain the N terminal sequence of E1A. The two isoforms of lens E1 are therefore translated from a single mRNA. Specifically, E1A is translated from the first initiation codon, and E1B translated from the second initiation codon. E1A and E1B were affinity-purified, and their ability to 'charge' ubiquitin carrier proteins (E2s) with activated ubiquitin was compared in a cell-free system. E1A and E1B were indistinguishable with respect to charging different E2s. However, E1 immunolocalization studies with human lens epithelial cells indicate that E1A and E1B are preferentially localized to the nucleus and cytosol, respectively. This observation suggests that E1A and E1B ubiquitinate different proteins and serve different functions in intact cells.

H(2)O(2)-mediated oxidative stress activates NF-kappa B in lens epithelial cells

In the mammalian lens, intracellular oxidants produced by photo-oxidative processes and exposure to toxic chemicals constitute stresses that produce cellular oxidative damage, result in changes in gene expression, and are causally related to cataract formation. Currently, it is believed that H(2)O(2) is the major oxidant to which the lens is exposed. In this report, we examine the activation and regulation of the oxidant-sensitive transcription factor, NF-kappa B, by H(2)O(2)-mediated oxidative stress in lens epithelial cells. Lens epithelial cells treated with H(2)O(2) demonstrated at 1 h a strong activation of NF-kappa B which returned to basal levels by 2 h. Under proteasome inhibition using both MG132 and lactacystin, H(2)O(2)-mediated activation of NF-kappa B was prevented, implicating the involvement of proteasome degradation of I kappa B proteins as being necessary for this activation. However, Western blot analysis demonstrated no degradation of I kappa B-alpha, -beta, or -epsilon associated with H(2)O(2)-mediated NF-kappa B activation. In comparison, when cells were treated with the cytokine TNF-alpha, NF-kappa B was strongly activated and degradation of both I kappa B-alpha and -beta was observed. These results clearly demonstrate that H(2)O(2)-mediated oxidative stress activates NF-kappa B in lens epithelial cells, which may subsequently lead to changes in gene expression. The results also reveal that different signaling pathways in the activation of NF-kappa B in lens epithelial cells are utilized by H(2)O(2) and TNF-alpha. These different pathways of NF-kappa B activation may be required to effect specific NF-kappa B-dependent gene expression in response to these different stimuli.

Removal of oxidatively damaged proteins from lens cells by the ubiquitin-proteasome pathway

Understanding how oxidized proteins are removed is important since accumulation of such damaged proteins is causally related to cellular and organismic dysfunction, disease and aging. Previous work showed that activity of the ubiquitin-proteasome pathway (UPP) in lens cells increased during recovery from oxidative stress ( Shang et al., 1997b : J. Biol. Chem. 272, 23086-93). In this study we sought to determine if the up-regulation of the UPP during recovery from oxidative stress has a role in selective removal of oxidized proteins from the cells. In cells which were not exposed to peroxide, inhibition of the proteasome with MG132 or clasto-lactacystin beta-lactone had little effect on protein carbonyl levels. However, inhibition of the proteasome in the 20 microM peroxide-treated cells caused an approximate 60% increase in levels of protein carbonyl and an approximate 100% increase in levels of ubiquitin conjugates. The carbonyl-containing proteins that accumulated in the presence of the proteasome inhibitor co-localized with high molecular mass ubiquitin-protein conjugates. Furthermore, isolated carbonyl-containing proteins from H2O2-treated cells were ubiquitinated, and ubiquitin-conjugates were enriched with carbonyl-containing proteins. The diminished effect of proteasome inhibitors on protein carbonyl levels, together with the robust increase in ubiquitin-protein conjugates and accompanied increases in oxidized proteins, upon exposure to 60 microM H2O2 indicate that the proteasomal step of the UPP is more susceptible to oxidative inactivation than the ubiquitination step. In fact, oxidative stress is associated with a hyperactivation of the ubiquitin-activating enzyme. These data indicate that the UPP plays a role in removal of oxidatively damaged proteins from cells and that attenuation of the UPP activity may result in cytotoxic accumulation of damaged proteins, possibly including the ubiquitinated forms.

Bufokinin: actions and distribution in the toad cardiovascular system

1. Bufokinin is a substance P-like neuropeptide and potent spasmogen isolated from the intestine of the cane toad Bufo marinus. In the present study, we investigated the effects of bufokinin on systemic blood pressure and heart rate in the anaesthetized toad and the distribution of bufokinin-like immunoreactivity in the toad vasculature. 2. Intravenous bufokinin caused a dose-dependent fall in systemic blood pressure (maximum fall 20 mmHg) with an ED50 of 2.9 pmol. At higher doses, the effect was prolonged and blood pressure did not return to baseline within 60 min. There was no significant change in heart rate associated with hypotension. 3. Bufokinin-like immunoreactivity was mapped in whole mounts of toad blood vessels and organs using a mouse polyclonal antibody BK3 (at 1:5000) and the avidin-biotin method. Bufokinin-immunoreactive fibres were associated with most blood vessels examined: a moderately dense perivascular network of varicose fibres was present around renal arteries, with sparser immunoreactive fibres in the ventral aorta, sciatic artery, anterior abdominal vein and hepatic portal vein. 4. Bufokinin-immunoreactive fibres, mainly following blood vessels, were seen in whole mounts of the urinary/bladder and tongue, but not in the air sac. In the heart ventricle, varicose fibres were found in the valve cusps, intracardiac ganglia, epicardium and myocardium close to the endocardium, but not in the rest of the myocardium. 5. The vasodepressor action of bufokinin and the presence of bufokinin-like immunoreactivity in varicose fibres in various vessels suggest a role for bufokinin in haemodynamic regulation and/or sensory nerve function in the toad. The lack of any reflex tachycardia in response to the falls in blood pressure was of note.

Bufokinin: immunoreactivity, receptor localization and actions in toad intestine and mesenteric circulation

In this study, we have mapped the immunoreactivity and the binding sites for bufokinin, a tachykinin peptide from the toad intestine. Dense bufokinin-immunoreactive fibers were present at the myenteric plexus, but no cell bodies were stained, suggesting an extrinsic origin. Bufokinin nerve fibers were also associated with submucosal blood vessels and mesenteric arteries. Autoradiographic binding sites for [(125)I]Bolton-Hunter-bufokinin were densely localized over the intestinal circular and longitudinal muscle, submucosal blood vessels and the endothelium of mesenteric arteries. Mesenteric veins had minimal immunoreactivity and binding sites. In the anesthetized toad, topical application of bufokinin onto the mesentery caused a 2.7-fold increase in arterial blood flow, observed using intravital microscopy. This study supports a role for bufokinin as an endogenous spasmogen and hemodynamic regulator in the toad intestine.

Autoradiographic localization of tachykinin and calcitonin gene-related peptide receptors in adult urinary bladder

PURPOSE

In bladder, sensory afferent nerve fibers contain the "sensory neuropeptides" substance P (SP), neurokinin A (NKA) and calcitonin gene-related peptide (CGRP), which interact with tachykinin NK-1 and NK-2 receptors and CGRP receptors, respectively. The purpose of this study was to examine the autoradiographic distribution of these three receptor types in the human bladder, to determine whether the anatomic location of the receptors was consistent with their known functional roles.

MATERIALS AND METHODS

Specimens of urinary bladder from 9 patients (58-74 years) were obtained at cystectomy. Frozen sections of dome were labeled with [125I]-Bolton-Hunter [Sar9,Met(O2)11]-SP (NK-1 receptors), [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10) (NK-2 receptors) and [125I]-rat CGRP-I. Binding sites were visualized using emulsion autoradiography.

RESULTS

NK-1 receptors were found over the endothelium of arterial blood vessels within the detrusor muscle and lamina propria, and over small vessels in the subepithelium. NK-2 receptors were seen over the detrusor muscle and very sparsely over blood vessels, whereas CGRP receptors were expressed densely over the smooth muscle layer of arteries and arterioles, and weakly over collecting venules. NK-1 and CGRP receptors were not observed over the detrusor muscle.

CONCLUSIONS

Although the afferent nerves contain all three peptides, not all cell types express receptors for each peptide. The general distribution of receptors is in good agreement with the location of nerves, and with the known actions of SP and CGRP as vasodilator agents, and of NKA (but not SP or CGRP) in contracting the detrusor muscle.

Decreasing ascorbate intake does not affect the levels of glutathione, tocopherol or retinol in the ascorbate-requiring osteogenic disorder shionogi rats

Levels of glutathione in liver and kidney, and other nutrients in plasma were evaluated in male and female ascorbate-requiring osteogenic disorder Shionogi (ODS) rats fed semipurified diets in which the concentrations of ascorbate were gradually decreased from 1965 to 180 mg/kg. Plasma ascorbate levels in ODS rats were unaffected when ascorbate levels in the diet were decreased from 1965 to 768 mg/kg. However, plasma ascorbate levels decreased progressively when levels of ascorbate in the diet were decreased from 527 to 180 mg/kg. Plasma ascorbate levels decreased up to 77% when the dietary ascorbate concentration decreased from 1965 to 180 mg/kg. Ascorbate levels in liver and kidney fell as much as 60-70% when the dietary ascorbate levels were reduced from 1965 to 180 mg/kg. However, the glutathione levels in these tissues were not affected. Plasma retinol and vitamin E levels were not affected by decreasing dietary ascorbate intake. Total cholesterol levels increased significantly in female rats as dietary ascorbate intake declined. Levels of glycated hemoglobin decreased significantly when dietary ascorbate levels decreased from 1965 to 527 mg/kg. This study suggests that levels of vitamin E, retinol and glutathione are not affected by decreased dietary intake of ascorbate under nonscorbutic conditions, whereas elevated ascorbate intake is associated with a decrease in levels of plasma cholesterol in female ODS rats. However, excessive intake of ascorbate may be associated with elevated glycation of hemoglobin. To achieve the maximal health benefit of ascorbate supplementation, further studies are necessary to define optimal ascorbate intakes.

Ubiquitin-dependent pathway is up-regulated in differentiating lens cells

The mammalian eye lens is composed of two distinct types of cells, epithelial cells and fiber cells. The fiber cells are generated throughout life via continuous differentiation of epithelial cells. Differentiation of lens cells involves dramatic changes in cellular components including altered activity of the ubiquitin dependent pathway. The concentration of high mass ubiquitin conjugates in the mitotically active-, differentiating-equatorial epithelial cells was 5-10 fold higher than that observed in mitotically quiescent, non-differentiated, central epithelial cells, even though there was a significant dilution of non-crystallin proteins due to an increase in level of crystallins in the differentiating cells. Similar observations were made when differentiation was modeled by exposure of lens epithelial explants to bFGF in culture. Activities of ubiquitin-activating enzyme (E1) and ubiquitin-conjugating enzymes (E2s) in the differentiating equatorial epithelial cells were also up to 100% higher than those noted in non-differentiated central epithelial cells and E1 appears to be rate controlling for ubiquitinylation. Consistent with the higher concentrations of high mass ubiquitin conjugates, there was a trend of enhanced ability to execute ATP-dependent protein degradation in the differentiating equatorial epithelial cells as compared with degradation in the non-differentiated central epithelial cells. These data indicate that the ubiquitin dependent pathway is up-regulated during differentiation of lens cells. In the differentiated fibers, the concentration of high mass ubiquitin conjugates and relative activities of E1 and E2s were 50% lower than in the non-differentiated central epithelial cells. In comparison, the concentration of the 110 kDa E1 was unchanged in differentiated fibers. However, if the factor of dilution by the significant increase in the level of crystallins was taken into account, the level or activities of the components of ubiquitin pathway in the differentiated cells was higher than the level noted in non-differentiated cells. These data indicate that, as compared with other non-crystallin proteins, there is differential stabilization and/or synthesis of the 110 kDa E1 and some other components of the ubiquitin dependent pathway in differentiated fibers.

Calorie restriction, stress and the ubiquitin-dependent pathway in mouse livers

Calorie restriction (R) is the only known method to delay the aging process and extend mean and maximal lifespan in rodents. R has been shown to delay the age-related accumulation of damaged proteins and to protect organisms from various stresses which can produce damaged proteins. Such stresses include irradiation, heat shock, and oxidative stress. The ubiquitin- and ATP-dependent proteolytic pathway (UPP) has been associated with the degradation of abnormal and/or damaged proteins. We examined the effect of diet and oxidative stress on activities of the UPP in supernatants from livers taken from 23-month-old Emory mice which had been exposed to an in-vivo injection of paraquat. Paraquat induces oxidative stress by generating superoxide radicals. In livers from non-stressed animals, steady-state levels of endogenous ubiquitin conjugates, de novo conjugate formation, and E1 and E2 activities were significantly lower in R animals than in control (C) animals. However, after exposure to paraquat, levels of endogenous ubiquitin conjugates were significantly higher in R versus C animals, and de novo conjugate formation and E1 and E2 activities in R animals rose to levels which were indistinguishable from levels of these activities noted in C animals. R was associated with an increased ability to degrade beta-lactoglobulin by the UPP after an oxidative stress was imposed. Ability to degrade beta-lactoglobulin by the C or R livers in non-stressed animals was not significantly different. Taken together, these data indicate that oxidative stress in R animals is associated with enhanced levels of ubiquitin conjugates and that this enhancement may be due to an increase in UPP activity. These data also indicate that the ability to form ubiquitin conjugates and the UPP system does not change with oxidative stress in C animals. The latter is consistent with prior reports that suggests that older C animals may already be in a state of enhanced oxidative stress and that activities of the UPP provide a sensitive indicator of levels of cellular redox status.

Redox regulation of ubiquitin-conjugating enzymes: mechanistic insights using the thiol-specific oxidant diamide

The ubiquitin-proteasome pathway (UPP) regulates critical cell processes, including the cell cycle, cytokine-induced gene expression, differentiation, and cell death. Recently we demonstrated that this pathway responds to oxidative stress in mammalian cells and proposed that activities of ubiquitin-activating enzyme (E1) and ubiquitin-conjugating enzymes (E2s) are regulated by cellular redox status (i.e., GSSG:GSH ratio). To test this hypothesis, we altered the GSSG:GSH ratio in retinal pigment epithelial cells with the thiol-specific oxidant, diamide, and assessed activities of the UPP. Treatment of cells with diamide resulted in a dose-dependent increase in the GSSG:GSH ratio resulting from loss of GSH and a coincident increase in GSSG. Increases in the GSSG:GSH ratio from 0.02 in untreated cells to > or = 0.5 in diamide-treated cells were accompanied by dose-dependent reductions in the levels of endogenous Ub-protein conjugates, endogenous E1-ubiquitin thiol esters, and de novo ubiquitin-conjugating activity. As determined by the ability to form E1-ubiquitin and E2s-ubiquitin thiol esters, E1 and E2s were both inhibited by elevated GSSG:GSH ratios. Inhibition of E1 was associated with the formation of E1-protein mixed disulfides. Activities of E1 and E2s gradually recovered to preoxidation levels, coincident with gradual recovery of the GSSG:GSH ratio. These data support S-thiolation/dethiolation as a mechanism regulating E1 and E2 activities in response to oxidant insult. Ubiquitin-dependent proteolytic capacity was regulated by the GSSG:GSH ratio in a manner consistent with altered ubiquitin-conjugating activity. However, ubiquitin-independent proteolysis was unaffected by changes in the GSSG:GSH ratio. Potential adaptive and pathological consequences of redox regulation of UPP activities are discussed.

Aging, calorie restriction and ubiquitin-dependent proteolysis in the livers of Emory mice

Calorie restriction (R), the only known method to delay the aging process and extend mean and maximal lifespan, has been shown to delay the age-related decline in protein degradation. There are several proteolytic pathways. The ubiquitin- and ATP-dependent proteolytic pathway (UPP) is frequently associated with degradation of damaged abnormal and/or regulatory proteins. We examined the effect of aging and R on supernatants of livers taken from young (4.5 months) and old (23 months) Emory mice. Aging was associated with increased levels of endogenous ubiquitin conjugates, enhanced ability to form high molecular weight conjugates and ubiquitin activating (E1) and ubiquitin conjugating (E2) activity in the control (C) liver supernatants. The age-related increase in levels of endogenous ubiquitin conjugates in liver appears to be primarily due to increased E1 and E2 activities. R prevented the age-related increase in E1 and E2 activity, and thus prevented the age-related increase in levels of ubiquitin conjugates. In spite of the age-related increase in ubiquitin conjugates, no age-related changes in ubiquitin-dependent proteolytic pathway were observed in the C animals. R was associated with an enhanced ability (130%) to degrade beta-lactoglobulin by the ubiquitin-dependent proteolytic pathway in livers from 4.5-month-old animals relative to age-matched C livers. However, rates of the ubiquitin-dependent degradation of beta-lactoglobulin in the 23-month-old C and R animals were indistinguishable. There were no age- or diet-related differences in the ability to degrade another substrate, oxidized ribonuclease (RNase).

Antioxidant enzyme activities in lens, liver and kidney of calorie restricted Emory mice

Dietary calorie restriction extends both mean and maximum life span and retards age-related diseases, including eye lens cataract in Emory mice. The beneficial effects of calorie restriction have been hypothesized to reflect enhanced tissue antioxidant capacity. As a test of this hypothesis, we reared male and female Emory mice on control (C) or 40% calorie-restricted (R) diets. We then determined activities of total superoxide dismutase (T-SOD), Cu/Zn-SOD, Mn-SOD, glutathione peroxidase (GPx), glutathione reductase (GR) and catalase (CAT) in eye lens, liver and kidney of young (4.5 or 6 months), mature (11 or 12 months) and old (22 months) animals. Effects of diet, age and sex were evaluated by multi-factor ANOVA. Only kidney GR activities (mean +/- S.E.M.) were significantly enhanced with the R diet (R, 61 +/- 2 vs. C, 54 +/- 3 U/mg protein; P = 0.03). More frequently, we noted reduced antioxidant enzyme activity in R as compared with C animals, including reduced activities of T-SOD in lens, liver and kidney, Cu/Zn-SOD in liver and kidney, liver Mn-SOD and liver CAT (P < 0.05). Effects of age on antioxidant enzyme activity in C mice included age-dependent decreases in lens and kidney CAT and in liver Mn-SOD. There was also an age-dependent increases in liver and kidney Cu/Zn-SOD and liver GR. None of these age-dependent alterations in antioxidant enzyme function were attenuated in tissues of mice fed the R diet. Values for liver CAT were significantly lower in females than in males (P = 0.05). These results indicate that antioxidant enzyme activities in Emory mouse tissues are influenced by diet, age and sex. However, it is unlikely that increased lifespan and attenuation of cataract (and perhaps other age-dependent debilities), which are associated with the R diet in the Emory mouse, are due to enhanced antioxidant enzyme capabilities.

Regulation of ubiquitin-conjugating enzymes by glutathione following oxidative stress

Upon oxidative stress cells show an increase in the oxidized glutathione (GSSG) to reduced glutathione (GSH) ratio with a concomitant decrease in activity of the ubiquitinylation pathway. Because most of the enzymes involved in the attachment of ubiquitin to substrate proteins contain active site sulfhydryls that might be covalently modified (thiolated) upon enhancement of GSSG levels (glutathiolation), it appeared plausible that glutathiolation might alter ubiquitinylation rates upon cellular oxidative stress. This hypothesis was explored using intact retina and retinal pigment epithelial (RPE) cell models. Exposure of intact bovine retina and RPE cells to H2O2 (0.1-1.7 micromol/mg) resulted in a dose-dependent increase in the GSSG:GSH ratio and coincident dose-dependent reductions in the levels of endogenous ubiquitin-activating enzyme (E1)-ubiquitin thiol esters and endogenous protein-ubiquitin conjugates and in the ability to form de novo retinal protein-125I-labeled ubiquitin conjugates. Oxidant-induced decrements in ubiquitin conjugates were associated with 60-80% reductions in E1 and ubiquitin-conjugating enzyme (E2) activities as measured by formation of ubiquitin thiol esters. When GSH levels in RPE cells recovered to preoxidation levels following H2O2 removal, endogenous E1 activity and protein-ubiquitin conjugates were restored. Evidence that S thiolation of E1 and E2 enzymes is the biochemical link between cellular redox state and E1/E2 activities includes: (i) 5-fold increases in levels of immunoprecipitable, dithiothreitol-labile 35S-E1 adducts in metabolically labeled, H2O2-treated, RPE cells; (ii) diminished formation of E1- and E2-125I-labeled ubiquitin thiol esters, oligomerization of E225K, and coincident reductions in protein-125I-labeled ubiquitin conjugates in supernatants from nonstressed retinas upon addition of levels of GSSG equivalent to levels measured in oxidatively stressed retinas; and (iii) partial restoration of E1 and E2 activities and levels of protein-125I-labeled ubiquitin conjugates in supernatants from H2O2-treated retinas when GSSG:GSH ratios were restored to preoxidation levels by the addition of physiological levels of GSH. These data suggest that the cellular redox status modulates protein ubiquitinylation via reversible S thiolation of E1 and E2 enzymes, presumably by glutathione.

Development of commissural neurons in the wallaby (Macropus eugenii)

We have examined the development of the laminar and areal distribution of cortical commissural neurons in a marsupial mammal, the wallaby Macropus eugenii. In this species, commissural axons approach the major cerebral commissure, the anterior commissure, via either the internal capsule or the external capsule and first cross the midline at postnatal day 14 (P14). By retrogradely labelling these axons with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI) at P15, we show here that the cell bodies of these neurons are restricted to a region of cortex adjacent to the rhinal fissure. Most of these labelled neurons are located in the compact cell zone of the cortical plate, with only a few labelled cells found in the zone of loosely packed cells deep to this layer. Over the subsequent 66 days, commissural neurons are found progressively more dorsally, rostrally, and caudally, so that, by P80, they are present throughout the extent of the neocortex. At this age, they are mainly pyramidal in morphology and form a single band within the deeper part of layer 5 of the developing cortex. From P80 to adulthood, the distribution of commissural neurons has been assessed in the visual cortex by using retrograde transport of horseradish peroxidase. At P80, labelled neurons with immature pyramidal morphology are present throughout the occipital cortex; as in DiI material, somata are located in deep layer 5. At P165, previously shown to be the age when commissural axon numbers peak, widespread labelling is present in the occipital region, with labelled cells now found in two bands corresponding to layers 3 and 5. After this age, neurons become more restricted in distribution, so that, by adulthood, commissural neurons are no longer apparent throughout area 17 but are restricted to a localised region around the area 17/18 boundary. Within this region, labelling is still present in layers 3 and 5 but is more dense in layer 3. The gradual restriction of commissural fields seen here in the wallaby is similar to that reported in the neocortex in many eutherians. These findings also support studies in eutheria, suggesting that subplate neurons do not appear to play a major role in commissural development.

Activity of ubiquitin-dependent pathway in response to oxidative stress. Ubiquitin-activating enzyme is transiently up-regulated

Relations between the ubiquitin pathway and cellular stress have been noted, but data regarding responses of the ubiquitin pathway to oxidative stress are scanty. This paper documents the response of this pathway to oxidative stress in lens cells. A brief exposure of lens epithelial cells to physiologically relevant levels of H2O2 induces a transient increase in activity of the ubiquitin-dependent pathway. Ubiquitin conjugation activity was maximal and increased 3. 5-9.2-fold over the activity noted in untreated cells by 4 h after removal of H2O2. By 24 h after removal of H2O2, ubiquitin conjugation activity returned to the level noted in untreated cells. In parallel to the changes in ubiquitin conjugation activity, the activity of ubiquitin-activating enzyme (E1), as determined by thiol ester formation, increased 2-6.7-fold during recovery from oxidation. Addition of exogenous E1 resulted in an increase in ubiquitin conjugation activity and in the levels of ubiquitin carrier protein (E2)-ubiquitin thiol esters in both the untreated cells and the H2O2-treated cells. These data suggest that E1 is the rate-limiting enzyme in the ubiquitin conjugation process and that the increases in ubiquitin conjugation activity which are induced upon recovery from oxidation are primarily due to increased E1 activity. The oxidation- and recovery-induced up-regulation of E1 activity is primarily due to post-synthetic events. Substrate availability and up-regulation of E2 activities also appear to be related to the enhancement in ubiquitinylation upon recovery from oxidative stress. The oxidation-induced increases in ubiquitin conjugation activity were associated with an increase in intracellular proteolysis, suggesting that the transient increase in ubiquitinylation noted upon recovery from oxidative stress may play a role in removal of damaged proteins from the cells.

Age-related decline in ubiquitin conjugation in response to oxidative stress in the lens

Accumulation of damaged proteins is a major age-related change in lenses of virtually all species and is associated with lens opacification. Proteolytic removal of the damaged proteins may play an important role in maintaining the transparency of the lens. In many tissues, selective removal of abnormal or damaged proteins occurs via a ubiquitin-dependent proteolytic pathway. Ubiquitin, an 8.5 kDa polypeptide, selectively binds to proteins to form ubiquitin-protein conjugates. This ubiquitin-protein conjugate is, in most cases, a signal for protein degradation. In this work, age-related changes in rat lens in the following aspects were detected: (a) levels of the ubiquitin-protein conjugates, (b) some of the enzymes involved in ubiquitin conjugation in rat lenses, and (c) ability to respond to oxidative damage. Endogenous ubiquitin-protein conjugates were detected in epithelium, cortex and nucleus of lenses from young and old rats. The levels of endogenous high molecular weight (HMW) ubiquitin-protein conjugates in each developmental zone of the lenses from young rats were higher than that in the counterparts of lenses from old animals. Peroxide-treatment generally resulted in elevated levels of endogenous HMW ubiquitin-protein conjugates although masses of bulk proteins remain unchanged. The increases in ubiquitin-protein conjugates in the epithelial sections of young and old lenses upon oxidative stress were comparable. In the cortex of young lenses, there was a significant oxidation-related increase in ubiquitin-protein conjugates. There was a similar trend but diminished response in the cortex of old lenses. Nuclear fibers from young lenses also showed an oxidation-induced increase in the level of ubiquitin-protein conjugates. This response was not observed in nuclear fibers of old lenses. The ability to form HMW-ubiquitin conjugates with exogenous 125I-labeled ubiquitin in the lens also increased upon oxidative stress. The extent of the increase in the de-novo ubiquitin conjugating activity upon exposure to oxidation in old lens was much smaller than in young lens. Ubiquitin-activating enzyme (E1), and ubiquitin conjugating enzymes (E2(17k), E2(20k) and E2(25k) were detected by thiol ester assays or Western blot analysis. No significant age-related changes in the levels of E1, E2(17k), E2(20k) and E2(25k) were detected. The activity of E1 and E2(17k) increased upon exposure to H2O2. These data indicate that lens has the ability to increase ubiquitin conjugation activity in response to oxidative stress and this ability is attenuated upon aging. The age-related decrease in the ability to mount a ubiquitin-dependent response upon oxidation may contribute to the accumulation of damaged proteins in the old lenses.

Peripheral and central predictors of whisker afferent morphology in the rat brainstem

Prior studies suggest that whisker afferents have but one central projection pattern, despite their association with differing peripheral receptors that predict central morphology in other systems. Target factors in barrelettes are thought to dictate afferent projection patterns; yet, barrelettes differ in their size, shape and development. We tested the hypothesis that whisker afferents have differing morphologies that are predicted by peripheral and central factors. Branching patterns and collaterals of 78 Neurobiotin-stained afferents were compared in rats. Fibers from one whisker had precisely somatotopic projections but highly varied morphologies. For the entire sample, analysis of variance revealed significant intrafiber variance in collateral number and arbor shape that was attributed to the target subnucleus. Significant interfiber variance did not reflect response adaptation rate, direction sensitivity, whisker row origin or parent fiber bifurcation in the trigeminal root. Instead, we found the following. 1) Mandibular fibers had more elongated arbors than maxillary axons. In subnuclei interpolaris and principalis, mandibular fibers had larger arbors with more boutons/collateral than maxillary axons; in oralis and interpolaris, mandibular fibers had fewer collaterals than those of the maxillary division. 2) Upper lip whisker axons had more boutons than those from the B-D row in all subnuclei. 3) Rostral whisker are afferents had larger arbors and more boutons than those from middle or caudal arcs due to significant arc effects in interpolaris and oralis. Thus, whisker afferents are not structurally uniform, and some morphological features are predictable. Intrafiber variance is attributed to the central target; interfiber variance reflects maxillary versus mandibular origin, upper lip origin and whisker rostrocaudal arc.

Degradation of differentially oxidized alpha-crystallins in bovine lens epithelial cells

There is a growing consensus that altered proteins are more susceptible to degradation than native proteins. The enhancement of degradation of damaged proteins may be of significance since it prevents the accumulation of damaged proteins in cells. Several proteolytic pathways have been discovered in the lens. These include ATP-independent, ATP-dependent and ATP/ubiquitin-dependent proteolytic pathways. However, the extent of involvement of these proteolytic pathways in degradation of damaged proteins is not well described. alpha-Crystallin was oxidized by exposure to 0.03-3.2 mol.OH (mol protein)-1. Modifications to the oxidized alpha-crystallin and proteolytic susceptibility of the oxidized alpha-crystallin were studied. Exposure to > 0.32 mol.OH per mole of subunit produced aggregates and fragments of alpha-crystallin. Changes in isoelectric points of the proteins were observed after exposure to 0.64 mol.OH (mol protein)-1. The extent of loss of tryptophan and sulfhydryl groups was related to the level of .OH-exposure. Carbonyl content increased progressively with increasing oxidation. When incubated with a supernatant of bovine lens epithelial cells, the .OH-modified proteins were proteolytically degraded up to three times faster than untreated alpha-crystallin. ATP stimulated the degradation of native alpha-crystallin and alpha-crystallin which was exposed to 1.6 mol.OH (mol subunit protein)-1 (alpha 1.6). Sixty-seven per cent and 100% of the ATP-dependent degradation of native alpha-crystallin and alpha 1.6 was ubiquitin-dependent, respectively. The data indicate that alpha-crystallins oxidized by .OH are recognized and degraded rapidly by cytoplasmic proteolytic systems in bovine lens epithelial cells. Both ATP-independent and ATP/ubiquitin-dependent proteolytic pathways are involved in the degradation of native and oxidized alpha-crystallin.

Oxidative stress and recovery from oxidative stress are associated with altered ubiquitin conjugating and proteolytic activities in bovine lens epithelial cells

Roles for ubiquitin (an 8.5 kDa polypeptide) involve its conjugation to proteins as a signal to initiate degradation and as a stress protein. We investigated ubiquitin conjugation and ubiquitin-dependent proteolytic activities in cultured bovine lens epithelial cells (BLECs) upon oxidative challenge. A 44% decrease in intracellular glutathione confirmed oxidative stress upon incubation with 1 mM H2O2. After 30 min incubation, endogenous high-molecular-mass ubiquitin conjugates decreased 73%, and intracellular proteolysis decreased about 50%. In the supernatants of the oxidatively treated BLECs, the ability to form high-molecular-mass ubiquitin conjugates with exogenous 125I-labelled ubiquitin decreased 28%, and ATP-dependent degradation of oxidized alpha-crystallin decreased 36%. When the H2O2-treated BLECs were allowed to recover for 60 min, intracellular proteolysis returned to the level of control cells. There was also a subsequent transient enhancement of intracellular proteolysis and a simultaneous recovery of endogenous high-molecular-mass ubiquitin conjugates. In parallel cell-free experiments, conjugating activity with exogenous 125I-labelled ubiquitin and ATP-dependent degradation of oxidized alpha-crystallin increased 35% and 72% respectively compared with non-oxidatively treated BLECs. ATP-independent proteolysis showed little response to exposure or removal of H2O2. These results indicate that (1) the rate of intracellular proteolysis in BLECs is associated with the level of endogenous high-molecular-mass ubiquitin conjugates and (2) oxidative stress may inactivate the ubiquitin conjugation activity with coordinate depression of proteolytic capability. Enhancement in ubiquitin conjugation and proteolytic activities during recovery from oxidative stress may be important in removal of damaged proteins and restoration of normal function of BLECs. The inactivation of ubiquitin-dependent proteolysis by oxidation may be involved in the accumulation of altered proteins and other adverse sequelae in the oxidatively challenged aging lens.

Degradation of native and oxidized beta- and gamma-crystallin using bovine lens epithelial cell and rabbit reticulocyte extracts

In many types of cells, modified proteins are selectively and rapidly removed by various proteolytic systems. In eye lens, as in most cells, there appears to be a multiplicity of proteolytic pathways, including ubiquitin-dependent, ATP-dependent and ATP-independent pathways. Each of these appears to be involved in the degradation of alpha-crystallins. The objective of this study was to determine if oxidized beta- and gamma-crystallins would be selectively degraded and which proteolytic systems might be involved. beta- and gamma-crystallins were oxidized by exposure to 137Cs radiation under N2O. This system generates *OH primarily. Oxidation of beta- and gamma-crystallins was indicated by decreased protein sulfhydryl content and tryptophan fluorescence, as well as by increased levels of carbonyl and high molecular weight aggregates with increasing radiation dose. gamma-crystallin was more susceptible than beta-crystallin to oxidation based on loss of native crystallin, increase in aggregates and fragmentation products, and loss of tryptophan. Low molecular mass polymers (dimers) appear to be the precursors of high mass aggregates induced upon oxidation. At a specific level of oxidative insult interchain covalent bonds in addition to disulfides were more extensive in the polymers of gamma-crystallin as compared to beta-crystallin. Except for beta-crystallin irradiated with 1 krad, the degradation rate of crystallins using both reticulocyte and bovine lens epithelial cells (BLEC) proteolytic systems increased in proportion to the extent of oxidation. Proteolysis of oxidized gamma-crystallins increased 1775% and 900%, respectively, using reticulocytes and BLEC supernatants as the source of proteases.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of monoclonal antibodies against the human immunodeficiency virus matrix protein, p17gag: identification of epitopes exposed at the surfaces of infected cells

Eight monoclonal antibodies reactive with the matrix protein of human immunodeficiency virus type 1 (HIV-1), p17gag, were isolated from rats which had been immunized with solubilized HIV-1 lysate. The epitope specificities of these antibodies were determined with a series of synthetic peptides representing overlapping regions of p17. Six of the antibodies were mapped to three distinct regions of p17, while two antibodies (G11g1 and G11h3) reacted only with intact recombinant p17, suggesting that they were directed against conformational or discontinuous epitopes. All the antibodies bound to HIV-infected cells which had been permeabilized with acetone, but only G11g1 and G11h3 reacted with live HIV-infected cells. Specificity studies with diverse virus strains demonstrated that these two antibodies recognized distinct epitopes, one which was group specific for HIV-1, and one which was shared with HIV type 2 and simian immunodeficiency virus. Binding competition studies indicated that these epitopes were proximal in native p17. Despite their reactivity with intact cells, these two antibodies did not possess appreciable virus-neutralizing activity. These results indicate that a form of p17 is expressed on the surfaces of live HIV-infected cells which is accessible to some, but not all, antibodies against p17. These cell surface molecules may play a role in the generation of antibodies against p17gag that are characteristic of early stages of HIV infection, and they may act as natural targets for the immune system and as potential targets for immunotherapy of HIV-infected cells.

A cytogenetic characterization comparing a rat 6TG-resistant strain and 6TG-sensitive clones

A 8.3 μ/ml 6-thioguanine (6TG)-resistant strain was isolated from a rat tetraploid cell line by step-by-step selection in 6TG-medium. In the 6TG-resistant cell population 51% of the cells were tetraploid and 35% of the cells were hypertetraploid, i.e., one chromosome more than a tetraploid. The 6TG-resistant strain grew very well in RPMI 1640 medium with intervals of three days between subcultures. The 6TG-resistant cells all have a homogeneously staining region (HSRs) in one of the X chromosomes which do not stain after chromosome C-banding. They also possess a higher NORs activity and much lower frequency of sister chromatid exchanges (SCE). When the 6TG-resistant RCT cells were subcultured in 6TG-free medium for three days, their SCE frequency did not change. 5'-bromodeoxyuridine (BrdU) significantly suppressed the NORs activity for both 6TG-resistant cells and 6TG-sensitive cells (P<0.001).