Unconventional secretion of α-Crystallin B requires the Autophagic pathway and is controlled by phosphorylation of its serine 59 residue

α-Crystallin B (CRYAB or HspB5) is a chaperone member of the small heat-shock protein family that prevents aggregation of many cytosolic client proteins by means of its ATP-independent holdase activity. Surprisingly, several reports show that CRYAB exerts a protective role also extracellularly, and it has been recently demonstrated that CRYAB is secreted from human retinal pigment epithelial cells by an unconventional secretion pathway that involves multi-vesicular bodies. Here we show that autophagy is crucial for this unconventional secretion pathway and that phosphorylation at serine 59 residue regulates CRYAB secretion by inhibiting its recruitment to the autophagosomes. In addition, we found that autophagosomes containing CRYAB are not able to fuse with lysosomes. Therefore, CRYAB is capable to highjack and divert autophagosomes toward the exocytic pathway, inhibiting their canonical route leading to the lysosomal compartment. Potential implications of these findings in the context of disease-associated mutant proteins turn-over are discussed.

Adenosine plasma level correlates with homocysteine and uric acid concentrations in patients with coronary artery disease

The role of hyperhomocysteinemia in coronary artery disease (CAD) patients remains unclear. The present study evaluated the relationship between homocysteine (HCys), adenosine plasma concentration (APC), plasma uric acid, and CAD severity evaluated using the SYNTAX score. We also evaluated in vitro the influence of adenosine on HCys production by hepatoma cultured cells (HuH7). Seventy-eight patients (mean age ± SD: 66.3 ± 11.3; mean SYNTAX score: 19.9 ± 12.3) and 30 healthy subjects (mean age: 61 ± 13) were included. We incubated HuH7 cells with increasing concentrations of adenosine and addressed the effect on HCys level in cell culture supernatant. Patients vs. controls had higher APC (0.82 ± 0.5 μmol/L vs 0.53 ± 0.14 μmol/L; p < 0.01), HCys (15 ± 7.6 μmol/L vs 6.8 ± 3 μmol/L, p < 0.0001), and uric acid (242.6 ± 97 vs 202 ± 59, p < 0.05) levels. APC was correlated with HCys and uric acid concentrations in patients (Pearson's R = 0.65 and 0.52; p < 0.0001, respectively). The SYNTAX score was correlated with HCys concentration. Adenosine induced a time- and dose-dependent increase in HCys in cell culture. Our data suggest that high APC is associated with HCys and uric acid concentrations in CAD patients. Whether the increased APC participates in atherosclerosis or, conversely, is part of a protective regulation process needs further investigations.

Assembly of HCV E1 and E2 glycoproteins into coronavirus VLPs

Hepatitis C virus (HCV) is believed to assemble by budding into membranes of the early secretory pathway, consistent with the membrane location where the viral envelope glycoproteins E1 and E2 accumulate when expressed. Coronavirus assembly also takes place at pre-Golgi membranes. Here, we generated coronavirus-like particles carrying in their envelope chimeric HCV glycoproteins composed of the ectodomains of E1 and E2, each fused to the transmembrane plus endodomain of the mouse hepatitis coronavirus spike glycoprotein. The chimeric particle system will enable structural and functional studies of the HCV glycoproteins.

Regression of left ventricular hypertrophy and improvement of diastolic function in hypertensive patients treated with telmisartan

OBJECTIVES

The study was designed to test whether or not the angiotensin II receptor blocker telmisartan brings about regression of left ventricular (LV) concentric hypertrophy and whether or not these changes are associated with improved diastolic filling.

METHODS

An echocardiographic follow-up study was performed in 85 hypertensive patients (systolic blood pressure [SBP] >140 mmHg, diastolic blood pressure [DBP] >90 mmHg) and mild-to-moderate LV hypertrophy (LV mass index related to body surface area [LVMI] 117-150 g/m2 for men and 105-150 g/m2 for women) treated with telmisartan monotherapy 40-80 mg once daily for 1 year. Blood pressure, LVMI, left atrial (LA) volumes, and diastolic function were determined at baseline and after 3, 6, 9, and 12 months of treatment. Blood pressure was also monitored at all visits. Diastolic function was assessed by examination of transmitral inflow and pulmonary vein flow patterns.

RESULTS

Telmisartan reduced blood pressure; after 12 months, the mean+/-S.D. SBP and DBP were reduced from 144+/-10 to 126+/-8 mmHg (p<0.001) and from 98+/-8 to 86+/-7 mmHg (p<0.001), respectively. The LVMI was decreased from 119+/-7 to 109+/-3 g/m2 (p<0.001) after 12 months' telmisartan treatment. All patients had diastolic dysfunction at baseline. After 12 months' telmisartan treatment, a normal pattern of transmitral inflow was present in 21% of patients. The regression of LV hypertrophy observed after 12 months was associated with increased peak early diastolic velocity/peak late diastolic velocity ratio from 0.60+/-0.18 to 0.83+/-0.20 (p<0.001), shortened isovolumic relaxation time (IVRT) from 110+/-13 to 105+/-13 ms (p<0.001), and decreased deceleration time from 229+/-30 to 215+/-28 ms (p=0.002). Univariate analysis showed that shortened IVRT was related to a reduction in the LVMI and LA maximal and minimal volumes. In the multivariate analysis, the reduction in LVMI and the reduction in LA maximal and minimal volumes were independently associated with IVRT reduction.

CONCLUSIONS

Telmisartan 40-80 mg is effective in LV hypertrophy regression in hypertensive patients. The reduction in LVMI due to telmisartan monotherapy was associated with a significant improvement of diastolic filling parameters and with a significant reduction of LA volumes.

Diethylsulphate and methylnitrosourea affect different targets in Chinese hamster fibroblasts: possible mechanisms of aneuploidy induction by these agents

It has been shown that the ethylating agent diethylsulphate (DES) induces centromere-containing micronuclei with kinetics suggesting that molecules other than DNA could be targets. In quiescent Chinese hamster fibroblasts CHEF/18, O6-alkylated bases inhibit ribosomal protein S6 kinase (S6K1), the terminal member of a kinase cascade responsible for an increased rate of protein synthesis, but not extracellular signal-activated kinases (ERK1/2) or terminal kinases of a second cascade which activates transcription. The inhibition correlates with the appearance of abnormal metaphases at the following mitosis, suggesting that alkylation of the nucleotide pool and inhibition of S6K1 could be one of the mechanisms leading to chromosome loss by alkylating agents. To clarify the role of protein kinases in chromosome loss induced by alkylating agents, we have studied the effects of DES and methylnitrosourea (MNU) on S6K1 and ERK1/2 activation by growth factors. The alkylating agents were studied in a battery of Chinese hamster fibroblasts (CHEF/18, CHO and ClB) with normal and mutated p53 to control for DNA damage-induced activation of p53, which could indirectly inhibit protein kinases. The role of repair in induction of micronuclei was studied in mismatch repair-proficient CHO and repair-deficient ClB cells. Our results indicate that DES induced micronuclei in a mismatch repair-independent manner, within 8 h of treatment, in agreement with a role for S6K1 inhibition in micronucleus formation. MNU induced centromere-containing micronuclei only in CHO cells, one cell cycle after treatment, without any detectable influences on either kinase cascade, suggesting a role for mismatch repair in chromosome loss.

The carboxyl-terminal valine is required for transport of glycoprotein CD8 alpha from the endoplasmic reticulum to the intermediate compartment

There is evidence that a carboxyl-terminal valine residue is an anterograde transport signal for type I transmembrane proteins. Removal of the signal would either delay glycosylation in the Golgi complex of proteins destined to recycle to the endoplasmic reticulum or determine accumulation in the endoplasmic reticulum of newly synthesized proteins destined for the plasma membrane. We used the human CD8 alpha glycoprotein to investigate the role of the carboxyl-terminal valine in the exocytic pathway. Using immunofluorescence light microscopy, metabolic labeling, and cell fractionation, we demonstrate that removal of the carboxyl-terminal valine residue delays transport of CD8 alpha from the endoplasmic reticulum to the intermediate compartment. Removal of the residue did not affect the other steps of the exocytic pathway or the folding/dimerization and glycosylation processes. Therefore, it is likely that this signal plays a role in the transport of CD8 alpha from the endoplasmic reticulum to the intermediate compartment either before or during the formation of the transport vesicles that drive the exit the protein from the endoplasmic reticulum.

Effects of simulated microgravity on metabolic activities related to DNA damage and repair in lymphoblastoid cells

We adopted a simple experimental framework to follow the dependence of structural aberrations and the modifications in selected metabolic processes correlated with the exposure of cells to microgravity. Alterations to the cellular metabolism induced by exposure to microgravity are evidentiated in the modification of PARP activity (strongly dependent to the presence of DNA damages and to the altered gene expression), in the modification of the repair ability and in the cell's energy homeostasis (NAD and ATP). Cells are exposed continuously to microgravity in a Random Positioning Machine (RPM) in complete medium for 48 hours. At the end of this period a part of these cells are immediately analysed for the parameters reported above and the remaining were furtherly incubated in standard laboratory conditions to document eventual defects during the phases of the recovery process. A part of cells, just after exposure to microgravity, were also subjected to treatment with a strong damaging agent, KBrO3, and these cells were subsequently analyzed. This final treatment was meant to amplify the eventual deficiencies experienced by microgravity-exposed cells in the DNA repair process also in dependence with the alterated metabolic conditions resulting after the exposure to microgravity.

Hepatitis C virus structural proteins reside in the endoplasmic reticulum as well as in the intermediate compartment/cis-Golgi complex region of stably transfected cells

The intracellular localization of hepatitis C virus structural proteins was analyzed by confocal immunofluorescence microscopy, cell fractionation, and immunoelectron microscopy in stably transfected cells that do not overexpress the viral proteins. The results strongly suggest that at steady state the structural proteins reside not only in the endoplasmic reticulum but also in the intermediate compartment and cis-Golgi complex region. By analogy with other viral systems, this finding raises the possibility that the intermediate compartment and cis-Golgi complex play a role in the assembly and budding of hepatitis C virus.

Micronucleus frequencies in exfoliated buccal cells in normal mucosa, precancerous lesions and squamous cell carcinoma

OBJECTIVE

To assess the value of micronuclei in the characterization of precancerous lesions of the oral cavity with reference to their likelihood of progressing to malignant lesions.

STUDY DESIGN

The frequency of micronuclei was determined in exfoliated cells from normal oral mucosa, a preneoplastic condition (leukoplakia) and precancerous lesions with and without dysplasia, squamous cell carcinomas and sites of previous carcinomas that had been removed.

RESULTS

Average micronucleus frequencies were increased in precancerous lesions as compared to normal mucosa and further increased in carcinomas, suggesting that micronuclei are a biomarker of neoplastic progression in this type of cancer. With all samples, micronucleus frequencies were systematically higher when cells were collected by vigorous than by light scraping, suggesting a decreasing gradient from basal to superficial layers of mucosa. The micronucleus frequency did not vary with the sex or age of patients, while it did vary with the anatomic site of the lesions.

CONCLUSION

Although the gradual increase in micronucleus counts from normal mucosa to precancerous lesions to carcinomas suggests a link of this biomarker with neoplastic progression, the large overlapping of data prevents its use as a predictor of progression of precancerous lesions to malignancy in individual patients.

Zinc transport and metallothionein secretion in the intestinal human cell line Caco-2

Caco-2, a human cell line, displays several biochemical and morphological characteristics of differentiated enterocytes. Among these is the ability to transport zinc from the apical to the basal compartment. This process was enhanced following exposure by the apical compartment to increasing concentrations of the metal. High pressure liquid chromatography fractionation of the media obtained from cells labeled with radioactive zinc showed that metallothioneins (MTs), small metal-binding, cysteine-rich proteins), were present in the apical and basal media of controls as well as in cells grown in the presence of high concentrations of zinc. Following exposure to the metal, the levels of Zn-MTs in the apical medium increased, while in the basal compartment the greatest part of zinc appeared in a free form with minor changes in the levels of basal MTs. Metabolic labeling experiments with radioactive cysteine confirmed the apical secretion of MTs. A stable transfectant clone of Caco-2 cells (CL11) was selected for its ability to express constitutively high levels of the mouse metallothionein I protein. This cell line showed an enhanced transport of the metal following exposure to high concentrations of zinc and a constitutive secretion of the mouse metallothionein I protein in the apical compartment. Together, these findings strongly support the hypothesis of a functional role between the biosynthesis and secretion of MTs and the transport of zinc in intestinal cells.

Defective nuclear localization of p53 protein in a Chinese hamster cell line is associated with the formation of stable cytoplasmic protein multimers in cells with gene amplification

Many p53 functions require p53 transport into the nucleus. Mutant p53 also generally accumulates in the nucleus of transformed or neoplastic cells. However, examples of cytoplasmic accumulation of wild-type or mutant p53 have also been reported. Various explanations have been provided for defective nuclear localization. Here we propose a novel example of cytoplasmic p53 localization which occurs in cells showing gene amplification and appears to be due to the formation of stable p53 multimers. We studied a methotrexate-resistant Chinese hamster cell line (MTX M) carrying amplified dihydrofolate reductase genes and derived from a cell line with p53 nuclear accumulation. MTX M showed cytoplasmic p53 localization and, on immunoblots, several extra bands in the high molecular weight region, besides the expected 53 kDa band. p53 localization and the appearance of high molecular weight bands appeared to be correlated with the degree of DNA amplification. However, amplification of dihydrofolate reductase itself was not involved. Changing the p53 phosphorylation status quantitatively influenced the formation of high molecular weight bands. Cell fusion experiments demonstrated that p53 cytoplasmic localization in MTX M is a dominant phenotype. This result suggests that the defect causing lack of nuclear localization in this cell line does not reside in the nucleus. In the cytoplasm of MTX M and of wild-type/MTX M heterodikaryons p53 gives rise to protein complexes that are unable to re-enter the nucleus. The formation of such protein complexes is dependent on the amplification of an unknown gene product.

Assembly of the CD8alpha/p56(lck) protein complex in stably expressing rat epithelial cells

We have previously characterized the biogenesis of the human CD8alpha protein expressed in rat epithelial cells. We now describe the biosynthesis, post-translational maturation and hetero-oligomeric assembly of the human CD8alpha/p56(lck) protein complex in stable transfectants obtained from the same cell line. There were no differences in the myristilation of p56(lck), or in the dimerization, O-glycosylation and transport to the plasma membrane of CD8alpha, between cells expressing either one or both proteins. In the doubly expressing cells, dimeric forms of CD8alpha established hetero-oligomeric complexes with p56(lck), as revealed by co-immunoprecipitation assays performed with anti-CD8alpha antibody. Moreover, p56(lck) bound in these hetero-oligomeric complexes was endowed with auto- and hetero-phosphorylating activity. The present study shows that: (1) the newly synthesized p56(lck) binds rapidly to CD8alpha and most of the p56(lck) is bound to CD8alpha at steady state; (2) CD8alpha/p56(lck) protein complexes are formed at internal membranes as well as at the plasma membrane; and (3) about 50% of complexed p56(lck) reaches the cell surface.

A new determinant of endoplasmic reticulum localization is contained in the juxtamembrane region of the ectodomain of hepatitis C virus glycoprotein E1

Hepatitis C virus glycoproteins E1 and E2 do not reach the plasma membrane of the cell but accumulate intracellularly, mostly in the endoplasmic reticulum. Previous studies based on transient expression assays have shown that the transmembrane domains of both glycoproteins are sufficient to localize reporter proteins in the endoplasmic reticulum and that other localization signals may be contained in the ectodomain of E1 protein. To identify such signals we generated chimeric proteins between E1 and two reporter proteins, the human CD8 glycoprotein and the human alkaline phosphatase, and analyzed their subcellular localization in stable as well as transient transfectants. Our results showed that (i) an independent localization determinant for the endoplasmic reticulum is present in the juxtamembrane region of the ectodomain of E1 protein and (ii) the localization dictated by this determinant is either due to direct retention or to a recycling mechanism from the intermediate compartment/cis-Golgi complex region, which is clearly different from those previously described for other retrieval signals. These results show for the first time in mammalian cells that the localization in the endoplasmic reticulum of transmembrane protein can be determined by specific targeting signals acting in the lumen of the compartment.

BCR-ABL prevents c-jun-mediated and proteasome-dependent FUS (TLS) proteolysis through a protein kinase CbetaII-dependent pathway

The DNA binding activity of FUS (also known as TLS), a nuclear pro-oncogene involved in multiple translocations, is regulated by BCR-ABL in a protein kinase CbetaII (PKCbetaII)-dependent manner. We show here that in normal myeloid progenitor cells FUS, although not visibly ubiquitinated, undergoes proteasome-dependent degradation, whereas in BCR-ABL-expressing cells, degradation is suppressed by PKCbetaII phosphorylation. Replacement of serine 256 with the phosphomimetic aspartic acid prevents proteasome-dependent proteolysis of FUS, while the serine-256-to-alanine FUS mutant is unstable and susceptible to degradation. Ectopic expression of the phosphomimetic S256D FUS mutant in granulocyte colony-stimulating factor-treated 32Dcl3 cells induces massive apoptosis and inhibits the differentiation of the cells escaping cell death, while the degradation-prone S256A mutant has no effect on either survival or differentiation. FUS proteolysis is induced by c-Jun, is suppressed by BCR-ABL or Jun kinase 1, and does not depend on c-Jun transactivation potential, ubiquitination, or its interaction with Jun kinase 1. In addition, c-Jun-induced FUS proteasome-dependent degradation is enhanced by heterogeneous nuclear ribonucleoprotein (hnRNP) A1 and depends on the formation of a FUS-Jun-hnRNP A1-containing complex and on lack of PKCbetaII phosphorylation at serine 256 but not on FUS ubiquitination. Thus, novel mechanisms appear to be involved in the degradation of FUS in normal myeloid cells; moreover, the ability of the BCR-ABL oncoprotein to suppress FUS degradation by the induction of posttranslational modifications might contribute to the phenotype of BCR-ABL-expressing hematopoietic cells.

Induction of apoptosis and inhibition of signalling pathways by alkylated purines

Addition of growth factors such as EGF and insulin to serum-starved G(0) Chinese hamster fibroblast cells results in activation of the phosphatidylinositol 3-kinase (PI3-K)/p70 S6 kinase (p70(S6K)) pathway and the ras-raf mitogen-activated kinase (MAPK) pathway. Activation of these pathways is usually associated with protection of cells from apoptosis. We have studied the effect of three alkylpurines, O(6)-methylguanine (O6meG), O(6)-ethylguanine (O6etG) and 6-dimethylaminopurine (6DMAP) on two particular steps of these pathways, namely activation of p70(S6K) and of MAPK. Under the same experimental conditions we studied the ability of these alkylpurines to induce apoptosis. Our results show that the three alkylpurines induced apoptosis with increasing efficiency from O6meG to 6DMAP to O6etG. The induction of apoptosis was phase specific, with the G(0)/G(1) phase being most sensitive. A reduced apoptotic response was observed in cells with abnormal nuclear accumulation of mutant or wild-type p53, suggesting that functional p53 was required for the induction of apoptosis. At concentrations inducing apoptosis the three alkylpurines inhibited p70(S6K) activity, while they had the opposite effect on MAPK. Rapamycin, a specific inhibitor of the p70(S6K) pathway, did not induce apoptosis at doses inhibiting p70(S6K) activity, suggesting that p70(S6K) is not directly involved in apoptosis. As expected, and in line with results reported by others, wortmannin, an upstream inhibitor of the p70(S6K) pathway, did induce apoptosis. We propose that activation of the MAPK pathway and simultaneous inhibition of the p70(S6K) pathway induce an apoptotic response in the cell.

Cell fractionation analysis of human CD8 glycoprotein transport between endoplasmic reticulum, intermediate compartment and Golgi complex in tissue cultured cells

We have set up an analytical cell fractionation procedure to dissect, by a non-morphological method, the anterograde transport of proteins from endoplasmic reticulum, intermediate compartment and Golgi complex in tissue cultured cells. Using this procedure after pulse-chase labelling of cells expressing human CD8 glycoprotein, we obtained results that: (1) support the view that the intermediate compartment is a distinct station in the export from the endoplasmic reticulum to the Golgi complex; and (2) strongly suggests that the O -glycosylation process starts after the intermediate compartment, presumably in the cis -Golgi complex.

Reduction of genotoxic effects of MNNG by butylated hydroxyanisole

Butylated hydroxyanisole (BHA) is a food preservative with markedly contradictory effects. On one side many studies showed its antimutagenic and anticarcinogenic effects but on the other side dietary levels of BHA were reported to cause gastrointestinal hyperplasia in rodents. We studied the influence of BHA on cytotoxicity, mutagenicity, and DNA-damaging activity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in Chinese hamster V79 cells cultured in vitro. Our results showed that BHA significantly reduced the frequency of 6-thioguanine resistant (6-TGr) mutations and micronuclei induced in V79 cells by MNNG. These antimutagenic effects of BHA were, however, accompanied by a very marked increase of MNNG toxicity and also slightly increased level of MNNG-induced DNA damage. For evaluation of toxicity we used three methods: (i) trypane blue exclusion; (ii) plating efficiency; and (iii) intensity of cellular macromolecule synthesis. The level of DNA damage was measured by the comet assay. On the basis of obtained results we suggest that BHA, which induces phase II detoxifying enzymes, probably doesn't reduce the level of DNA damage induced in time of MNNG-treatment but it reduces the level of DNA damage created during a long-term period needed for expression of 6-TGr mutations and micronuclei.

Sequence and expression of the monkey homologue of the ER-golgi intermediate compartment lectin, ERGIC-53

We obtained the cDNA sequence of the monkey homologue of the intermediate compartment protein ERGIC-53 by both cDNA library screening and RT-PCR amplification. The final sequence of 2422 nts of the monkey ERGIC-53 cDNA is 96.2% identical to the human ERGIC-53 cDNA and 87% and 67% identical to the rat and amphibian cDNA, respectively. The translated CV1 ERGIC-53 protein is 96.47% identical to the human ERGIC-53, 87% identical to the rat p58 and 66. 98% to the Xenopus laevis protein. Southern blot analysis of multiple genomic DNAs shows the presence of sequences similar to ERGIC-53 in different species. ERGIC-53 is expressed as a major transcript of about 5.5 kb in either monkey CV1 or in human CaCo2. A shorter transcript of 2.3 kb was detected in both cell lines and in mRNAs derived from human pancreas and placenta.

A different intracellular distribution of a single reporter protein is determined at steady state by KKXX or KDEL retrieval signals

To establish the specific contribution to protein topology of KKXX and KDEL retrieval motifs, we have determined by immunogold electron microscopy and cell fractionation the intracellular distribution at steady state of the transmembrane and anchorless versions of human CD8 protein, tagged with KKXX (CD8-E19) and KDEL (CD8-K), respectively, and stably expressed in epithelial rat cells (Martire, G., Mottola, G., Pascale, M. C., Malagolini, N., Turrini, I., Serafini-Cessi, F., Jackson, M. R., and Bonatti, S. (1996) J. Biol. Chem. 271, 3541-3547). The CD8-E19 protein is represented by a single form, initially O-glycosylated: only about half of it is located in the endoplasmic reticulum, whereas more than 30% of the total is present in the intermediate compartment and cis-Golgi complex. In the latter compartments, CD8-E19 colocalizes with beta-coat protein (COP) (COPI component) and shows the higher density of labeling. Conversely, about 90% of the total CD8-KDEL protein is localized in clusters on the endoplasmic reticulum, where significant co-localization with Sec-23p (COPII component) is observed, and unglycosylated and initially O-glycosylated forms apparently constitute a single pool. Altogether, these results suggest that KKXX and KDEL retrieval motifs have different topological effects on theirs own at steady state: the first results in a specific enrichment in the intermediate compartment and cis-Golgi complex, and the latter dictates residency in the endoplasmic reticulum.

Inhibition of the Mr 70,000 S6 kinase pathway by rapamycin results in chromosome malsegregation in yeast and mammalian cells

The antifungal and immunosuppressive drug rapamycin arrests the cell cycle in G1-phase in both yeast and mammalian cells. In mammalian cells, rapamycin selectively inhibits phosphorylation and activation of p70 S6 kinase (p70(S6K)), a protein involved in the translation of a subset of mRNAs, without affecting other known kinases. We now report that rapamycin causes chromosome malsegregation in mammalian and yeast cells. Chromosome malsegregation was determined by metaphase chromosome analysis of human lymphocytes and lymphoblasts, detection of CREST-positive micronuclei in human lymphoblasts and Chinese hamster embryonic fibroblast (CHEF) cells, and selection of doubly prototrophic cells in a specially constructed yeast strain. The number of ana-telophases with displaced chromosomes and interphase and mitotic cells with an irregular number of centrosomes was also determined in CHEF cells. In quiescent mammalian cells (human lymphocytes and CHEF cells) induced with growth factor to re-enter the cell cycle, rapamycin was effective when cells were exposed at the time of p70(S6K) activation. In yeast, rapamycin was more effective when treatment was started in G1- than in G2-synchronized cells. Cells from ataxia telangiectasia (A-T) patients are characterized by chromosome instability and have recently been found to be resistant to the growth-inhibiting effect of rapamycin. We found that an A-T lymphoblastoid cell line was also resistant to the induction of chromosome malsegregation by rapamycin, but the level of spontaneous aneuploidy was higher than in normal cells. In yeast, the induction of chromosome malsegregation was dependent on the presence of a wild-type TUB2 gene, encoding the beta-subunit of tubulin. The finding that rapamycin acts in different cell types and organisms suggests that the drug affects a conserved step important for proper segregation of chromosomes. One or more proteins required for chromosome segregation could be under the control of the rapamycin-sensitive pathway.

TLS/FUS, a pro-oncogene involved in multiple chromosomal translocations, is a novel regulator of BCR/ABL-mediated leukemogenesis

The leukemogenic potential of BCR/ABL oncoproteins depends on their tyrosine kinase activity and involves the activation of several downstream effectors, some of which are essential for cell transformation. Using electrophoretic mobility shift assays and Southwestern blot analyses with a double-stranded oligonucleotide containing a zinc finger consensus sequence, we identified a 68 kDa DNA-binding protein specifically induced by BCR/ABL. The peptide sequence of the affinity-purified protein was identical to that of the RNA-binding protein FUS (also called TLS). Binding activity of FUS required a functional BCR/ABL tyrosine kinase necessary to induce PKCbetaII-dependent FUS phosphorylation. Moreover, suppression of PKCbetaII activity in BCR/ABL-expressing cells by treatment with the PKCbetaII inhibitor CGP53353, or by expression of a dominant-negative PKCbetaII, markedly impaired the ability of FUS to bind DNA. Suppression of FUS expression in myeloid precursor 32Dcl3 cells transfected with a FUS antisense construct was associated with upregulation of the granulocyte-colony stimulating factor receptor (G-CSFR) and downregulation of interleukin-3 receptor (IL-3R) beta-chain expression, and accelerated G-CSF-stimulated differentiation. Downregulation of FUS expression in BCR/ABL-expressing 32Dcl3 cells was associated with suppression of growth factor-independent colony formation, restoration of G-CSF-induced granulocytic differentiation and reduced tumorigenic potential in vivo. Together, these results suggest that FUS might function as a regulator of BCR/ABL leukemogenesis, promoting growth factor independence and preventing differentiation via modulation of cytokine receptor expression.

Micronucleus analysis in peripheral blood lymphocytes from melanoma patients treated with dacarbazine

BACKGROUND

Dacarbazine is an antitumor drug used with considerable success in the chemotherapy of a number of human neoplasias, particularly advanced disseminated melanoma. Dacarbazine is mutagenic in prokaryotic and eukaryotic cells, but no effect in vivo have been evaluated.

MATERIALS AND METHODS

Peripheral blood lymphocytes from patients with metastatic melanoma undergoing dacarbazine chemotherapy every 21 days for a total of 7 cycles, were analyzed for the presence of micronuclei with the CREST antikinetochore antibody technique. Cytogenetic analysis on blood samples collected just before and 2 hours after the therapy was carried out at 48, 72 and 96 hours following lymphocyte stimulation.

RESULTS

A significant increase in micronucleus frequency was found at both 72 and 96 hours after therapy. For the only two patients analyzed after more than one cycle, a decrease in micronuclei was observed after the third and the fourth therapy. Moreover, the CREST antibody technique showed that the frequency of micronuclei containing whole chromosomes (CREST+) was significantly higher after therapy at 72 and 96 hours. As the frequency of micronuclei containing acentric chromosome fragments (CREST-) was not significantly increased after therapy, either at 72 or 96 hours after lymphocyte stimulation, we suppose that DTIC mainly acted as an aneugenic agent.

CONCLUSIONS

The lack of a significant micronucleus increase at 48 hours could suggest that this culture time is too short for providing cultures with a sufficient large number of diving cells. In conclusion, our results have shown that dacarbazine induced chromosome loss in lymphocytes from patients treated with this drug.

Fragile sites at the centromere of Chinese hamster chromosomes: a possible mechanism of chromosome loss

On the basis of our previous observations showing that fragile sites (FS) mapped essentially in the centromeric regions of Chinese hamster chromosomes, we consider the possibility that the presence of FS at the centromere might be a source of chromosome loss. In this model a centromeric FS causes a centromeric break giving rise to two chromosome arms which could be lost or maintained with different consequences on the ploidy of daughter cells. To test this hypothesis, Chinese hamster cells have been treated both with N-methyl-N-nitrosourea (MNU), a mutagenic agent which also induces aneuploidy, and vinblastin (VBL), a pure aneugen, used as a control compound, which is supposed not to interact with DNA. The results show that MNU induces the formation of translocated and/or truncated chromosomes, on the contrary VBL is not able to induce chromosome rearrangements. The sites most involved in MNU-induced breaks are the centromeric regions of chromosomes where FS are also present. These breaks cause essentially the loss of one chromosome arm, so that the resulting cells are numerically diploid but presenting partial monosomies. The implications of these results are discussed.

Induction of kinetochore positive and negative micronuclei in V79 cells by N-methyl-N'-nitro-N-nitrosoguanidine: the protective effect of the pyridoindole antioxidant stobadine

The induction of micronuclei by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and their reduction by the cardioprotective synthetic antioxidant, stobadine were studied in hamster V79 cells cultured in vitro. The micronuclei derived from acentric fragments or from whole chromosomes were evaluated with the help of an immunofluorescent staining using antikinetochore antibodies from the serum of scleroderma (CREST syndrome) patients. Our results showed that MNNG (0.5 microgram/ml) induced mainly kinetochore-negative micronuclei. At 6, 24 and 48 h after MNNG treatment, we measured a 2.7-, 4.3-, and 7.0-fold increase, respectively, of kinetochore-negative micronuclei over the controls. The increase of kinetochore-positive micronuclei was rather low and represented at 6, 24 and 48 h, respectively 0.9-, 1.8- and 2.6-fold increases over the controls. Stobadine decreased the level of kinetochore-negative micronuclei at 6, 24 and 48 h to approximately one-half; the frequency of kinetochore-positive micronuclei was reduced only at 6 h. We suppose that the antioxidant stobadine reduces the induction of micronuclei by MNNG by scavenging of MNNG-induced highly reactive OH radicals which cause chromosomal damage.

Staining of micronuclei in squamous epithelial cells of human oral mucosa

OBJECTIVE

To evaluate the influence of methodologic variables, staining method and sampling, on the frequency of micronuclei scored in squamous epithelial cells of oral mucosa. Micronuclei were used as biomarkers of structural and numerical chromosome damage.

STUDY DESIGN

Feulgen and Giemsa stain and fluorescent dyes Hoechst 33258 and propidium iodide were used for micronucleus staining. Cells were collected by either light or vigorous scraping of oral mucosa.

RESULTS

Staining of micronuclei by Hoechst 33258 proved more handly, less time consuming and at least equally reliable to the more widely used Feulgen staining. Results with Giemsa stain and propidium iodide were unsatisfactory. Micronuclei were less frequent in superficial layers of the oral mucosa.

CONCLUSION

Hoechst 33258 can be recommended for micronucleus staining in squamous epithelial cells of oral mucosa. Differences in scraping may affect the measurement of micronucleus frequency; scraping should therefore be carefully standardized in each laboratory.

Sister chromatid exchange induction in peripheral blood lymphocytes of traffic police workers

Traffic police workers, as a population exposed to urban atmosphere, were compared with a control population exposed to indoor air pollution levels. Sister chromatid exchanges (SCEs) as a biomarker of effect were measured in peripheral blood lymphocytes of 54 exposed subjects and 35 controls, and environmental concentration of polynuclear aromatic hydrocarbon (PAH) tracer compounds was detected by personal air samplers. The mean exposure level to benzo[a]pyrene in our group of traffic policemen (3.4 mg/m3) was in the range that has been estimated in urban areas in Europe during the last 10 years. No difference in SCE levels was found between exposed workers (7.36, SD 1.35) and controls (7.47, SD 1.28). No correlation was observed between SCE/cell and airborne PAH concentration in the traffic worker population. A positive regression of SCE on exposure estimate was found only in the non-smoking group of police workers. Our findings suggest that exposure to urban air pollution does not induce relevant cytogenetic effects.

6DMAP inhibition of early cell cycle events and induction of mitotic abnormalities

N-6 dimethylaminopurine (6DMAP) has been shown to induce aberrant mitosis in different cell types including Chinese hamster fibroblasts (CHEF/18). The mechanism of action and the cellular targets, however, are still not clear. We showed previously that in CHEF/18 cells this compound inhibits DNA synthesis with a kinetic of inhibition suggestive of an effect on early events of the cell cycle. In this paper we investigated which cellular targets were affected by 6DMAP and found that: (i) the compound inhibits phosphorylation of ribosomal protein S6 and activation of the 70 kDa S6 kinase (p70S6k) known to be activated by epidermal growth factor (EGF) in keeping with the notion that it is a protein kinase inhibitor; however the inhibition in vivo appears to be specific as MAP kinase phosphorylation is not inhibited; (ii) 6DMAP drastically affects cytoskeletal components leading to a rapid morphological change in most cells. These data, together with the findings that the dose range and the treatment time effective in inducing the micronuclei containing chromosomes were the same as for DNA synthesis inhibition, suggest that a disturbance in G1 of signal transduction pathways may contribute to abnormal mitosis.

Analysis of metal-regulated metallothionein and heat shock gene expression in HeLa-derived cadmium-resistant cells

The expression of metallothionein (MT) and heat shock protein gene families was investigated in normal and in HeLa-derived cadmium-resistant cells, named H454. In the absence of amplification of MT genes H454 cells accumulated elevated concentrations of cadmium ions and synthesized higher levels of MT proteins than unselected HeLa cells. Northern blot analyses revealed higher levels of MT mRNAs in the resistant cells than in wild-type cells after Cd2+ and Zn2+ exposure. Evaluation of the cytotoxic potential of the different metals confirmed the high resistance to cadmium of the H454 cells. Two proteins of the heat shock family, hsp70 and GRP78, were synthesized in Cd(2+)-exposed H454 cells at levels comparable to the ones present in Cd(2+)-treated normal cells. Northern blot analyses of the mRNA levels corresponding to these proteins revealed elevated expression of both hsp70 and GRP78 mRNAs in H454 cells upon exposure to cadmium ions and no response to zinc induction. These data suggest the existence in the H454 cells of a cadmium-specific pathway of regulation of MT and heat shock genes.

Morphological analysis of the transfer of VSV ts-045 G glycoprotein from the endoplasmic reticulum to the intermediate compartment in vero cells

Vero cells were infected with the ts-045 strain of vesicular stomatitis virus, and the cells were incubated at 39 degrees C to accumulate the mutant G glycoprotein in the ER as a misfolded aggregate. Cycloheximide was added to the culture medium 3.5 h after infection to prevent further protein synthesis, and the temperature was lowered to 10, 15, or 31 degrees C. At these temperatures, the mutant G glycoprotein correctly folds and oligomerizes. Immunofluorescence light microscopy showed that the G glycoprotein was exported to the Golgi complex at 31 degrees C and to the intermediate compartment (IC) at 15 degrees C, but no export was observed at 10 degrees C. However, incubations at 10 degrees C followed by shift to 15 or 31 degrees C resulted in the normal transfer of the glycoprotein to the IC and the Golgi, respectively. Immunoelectron microscopical analysis confirmed all these results, but showed also that the glycoprotein was frequently clustered in the ER at 10 degrees C. Conventional electron microscopy showed that the morphology of the ER, IC, and Golgi complex remained essentially unchanged at all temperatures. The only significant difference detectable in cells incubated at 10 degrees C was the increased number of partially coated ER protrusions, longer than those detected at higher temperatures. These results demonstrate that the transport toward the Golgi complex of G glycoprotein can be arrested at a step preceding the entry into the IC, thus suggesting that ER and IC are separate stations in the exocytic pathway.

p53 accumulates in micronuclei after treatment with a DNA breaking chemical, methylnitrosourea, and with the spindle poison, vinblastine

Micronuclei (MN) induced by N-methyl-N-nitrosourea (MNU) or vinblastine in cultured mammalian cells were analyzed for the accumulation of p53 by immunocytochemical staining with a p53 monoclonal antibody. Our data showed that MN induced by both agents were p53-negative at early post-treatment times, but became positive at late times. Assuming that most MNU-induced micronuclei reflect DNA damage, and most vinblastine-induced micronuclei reflect damage to the mitotic apparatus, we conclude that p53 accumulation in micronuclei is not triggered by DNA damage per se but instead probably stems from DNA degradation occurring during ageing of micronuclei.

Study on aneuploidy and p53 mutations in astrocytomas

To determine whether a correlation exists between aneuploidy and p53 status in astrocytic tumors we analyzed 48 astrocytomas with different grades of malignancy for the presence of p53 mutations and aneuploidy of chromosomes 10 and 17 (Ch10, Ch17), known to be particularly involved with this type of tumor. We used polymerase chain reaction (PCR)-based denaturing gradient gel electrophoresis (DGGE) analysis on exons 5-8 of the p53 gene, and fluorescence in situ hybridization (FISH) analysis on interphase nuclei using chromosome specific pericentromeric probes, respectively. Our results showed that Ch10/Ch17 aneuploidy is a common early event in astrocytomas (90% of low grade tumors are aneuploid). p53 mutations and Ch17 aneuploidy are early events, but their incidence is not dependent on tumor grade. Loss of Ch10 is the only alteration that significantly correlates with tumor progression. No significant correlation between the presence of Ch10/Ch17 aneuploidy and p53 mutations was found. However, the coexistence of p53 mutations and aneuploidy, was observed in a subset of cases. The presence of p53 mutations appeared to be a significant predictor of a poor prognosis. In conclusion, genomic instability may or may not be associated with p53 mutations in astrocytomas, thus suggesting that other cellular determinants can also be responsible for the aneuploidy observed.

[Cytogenetic indicators of genotoxicity in subjects occupationally exposed to antineoplastic drugs]

The paper reviews the main characteristics of the cytogenetic indicators most frequently used in monitoring early biological effects in groups exposed to genotoxic agents, i.e. chromosome aberrations (CA), sister chromatid exchanges (SCE) and micronuclei (MN) in lymphocytes. The results of the numerous studies on CA and/or SCE performed on hospital or industry personnel potentially exposed to antineoplastic drugs are conflicting, probably due to the different degrees of exposure in different occupational settings, to different sensitivity of the indicators or to their different persistence. However, the studies carried out on groups of subjects who have always worked in protected conditions have given negative results for all indicators.

Different fate of a single reporter protein containing KDEL or KKXX targeting signals stably expressed in mammalian cells

In mammalian cells, resident luminal and type I transmembrane proteins of the endoplasmic reticulum usually contain KDEL and KKXX at the carboxyl terminus. These sequences induce retrieval from compartments located downstream in the secretory pathway. It has been suggested that the retrieval may occur from multiple sites, ranging from the intermediate compartment to the trans-Golgi network. To compare the retrieval of luminal and type I membrane proteins, we have used different forms of a single reporter, the human CD8 glycoprotein, stably expressed in FRT cells. Metabolic labeling and oligosaccharide analysis show that the mechanism based on the KDEL signal is leaky. With time, the KDEL-containing CD8 form reaches the trans/trans-Golgi network compartments, where the protein is terminally glycosylated. At this stage, the retrieval mechanism stops being effective and the protein is consequently secreted. Conversely, the mechanism based on the KKXX signal guarantees that most of the KKXX-containing CD8 form resides in the endoplasmic reticulum, little in the Golgi complex and undetectable levels at the plasma membrane. The O-glycosylation of this protein comprises for the vast majority the sole addition of peptide-bound GalNAc that occurs in an early Golgi compartment.

Aflatoxin exposure and cytogenetic alterations in individuals from the Gambia, West Africa

Aflatoxin-albumin adducts in peripheral blood provide a measure of exposure to aflatoxin over the previous 2-3 months. In the present study, the levels of these adducts were determined in a group of individuals from The Gambia, West Africa and were compared in a cross-sectional study to the levels of various cytogenetic alterations (chromosomal aberrations, micronuclei, sister chromatid exchanges) in the same individuals to test whether an increase in genetic damage is associated with an increased exposure in this population. Of 35 subjects tested for aflatoxin-albumin adducts, all but 3 were positive. There were no correlations between the adduct level and the number of cytogenetic abnormalities at the individual level. A comparison of the cytogenetic alterations was made between Gambian individuals and a group of 22 healthy people from Italy where aflatoxin exposure is expected to be low. The levels of structural chromosomal aberrations, sister chromatid exchanges and micronuclei were all higher in the former group. Overall, these data are indicative of a higher exposure to genotoxins in Gambian subjects, one of which are aflatoxins, but suggest that more specific genetic markers of aflatoxin exposure are required to further examine the link between aflatoxin exposure and genetic alterations.

p53 expression in normal versus transformed mammalian cells

To answer the question whether the level of p53 expression also reflects the status of a cell, with reference to transformation and genome stability, we have examined, by immunocytochemistry, the presence of p53 protein in a number of cell types including human diploid cells, Chinese hamster embryonal cells at different passages and gene amplified and/or transformed Chinese hamster cell lines. Primary human fibroblasts at early passage (LEO) and an established, non transformed, Chinese hamster cell line at early passage (CHEF/18) did not show any detectable p53 expression, either nuclear or cytoplasmic. All transformed human (Raji) and Chinese hamster cell lines (CHO, V79, V79/B7) showed a nuclear expression of p53, although at different intensities. Two cell lines selected from V79/B7 for their resistance to phosphonacetyl-L-aspartate or methotrexate and previously shown to bear gene amplification, showed p53 expression. In PALA L cells p53 expression was nuclear as in other positive cell lines tested, while in MTX M cells it was cytoplasmic. CHEF/18 cells at late passage in culture showed the typical behaviour of transformed cells and p53 was detected in several cells. Moreover, when transformed CHO cells were treated with compounds known to induce reverse transformation, both the disappearance of hallmarks of transformed phenotype and p53 reduction were observed. These results indicate a strong association within the same cell type between p53 expression and transformed status.

Cytogenetic biomonitoring of styrene-exposed plastic boat builders

Earlier studies have produced evidence for an association between work-related styrene exposure and cytogenetic damage, while more recent studies have failed to show such an association. In the present study, chromosome aberrations (CA) and sister chromatid exchanges (SCE) were measured in peripheral blood lymphocytes of 46 male workers employed in a fiber-reinforced plastic boat building factory and exposed to styrene. Two groups of 23 workers each, characterized by different exposure levels (ranges: 2-120 mg/m3 and 86-1389 mg/m3 ambient air) were studied, fifty-one controls matched by sex, age and smoking habits were included. Randomized blood samples were analyzed for cytogenetic damage separately in two laboratories. Interlaboratory differences in the scoring of CA and SCE were noted. However, increases of the considered cytogenetic endpoints in exposed vs control groups were consistently observed in both laboratories. Multivariate statistical analysis of pooled data revealed increases of CA ranging between 19% (RR = 1.19; 95% C.I., 0.80-1.78; chromatid-type aberrations, low exposure group) and 144% (RR = 2.44; 95% C.I., 1.26-4.70; chromosome-type aberrations, high exposure group). Parallel excess of SCE in styrene exposed workers was also observed, although at a lesser extent (RR = 1.22; 95% C.I., 1.05-1.43, low exposure group; RR = 1.26; 95% C.I., 1.07-1.47, high exposure group). These findings suggest the presence of a causal association between occupational exposure to styrene and cytogenetic damage in the plastic boat building factory that was the object of the study.

Effect of ATP depletion and DTT on the transport of membrane proteins from the endoplasmic reticulum and the intermediate compartment to the Golgi complex

Newly synthesized membrane proteins are exported from the endoplasmic reticulum to the Golgi complex through an intermediate compartment. Incubation at low temperature (15 degrees C) arrests the proteins in the intermediate compartment and prevents the entry into the Golgi complex. We have studied, in living cells, the effect of dithiothreitol (DTT) and ATP depletion on the transport to the Golgi complex of proteins accumulated either in the endoplasmic reticulum or in the intermediate compartment after a temperature block. The morphological results obtained with vesicular stomatitis virus ts-O45 G glycoprotein and the biochemical analysis performed with human CD8 protein, an O-glycosylated protein, showed that: 1) ATP depletion blocks the export to the Golgi complex of proteins located either in the endoplasmic reticulum or in the intermediate compartment and ii) DTT interferes with the folding and export of proteins located in the endoplasmic reticulum, but it does not prevent the transfer from the intermediate compartment to the Golgi complex.

The induction of aneuploidy by alkylated purines: effects on early and late cell cycle events

It has been shown that alkylated bases induce aneuploidy in mammalian cells in culture. The mechanism of action is not clear, however, data with 6-dimethyl amino purine (6DMAP) suggest that this analogue might act by affecting the cytoskeleton and protein kinases involved in cell cycle regulation (cdc2/p34). The aim of this work was to study the effect of O6methylguanine (O6meG), O6ethylguanine (O6etG) and 6DMAP on DNA synthesis induced by growth factors in two cell lines, 3T3 and CHEF/18 fibroblasts, which respond in opposite ways to substances affecting the cytoskeleton, colchicine and cholera toxin: DNA synthesis initiation is stimulated in 3T3 cells and inhibited in CHEF/18 cells by such compounds. Our results indicate that O6meG and O6etG behave like cholera toxin, in as much as they inhibit DNA synthesis induced by epidermal growth factor plus insulin in CHEF/18 cells, and stimulate it in 3T3 cells. 6DMAP behaves differently and inhibits DNA synthesis in both cell lines. The inhibition (or stimulation) was greater when alkylated bases were added before S phase started, suggesting that these compounds might affect early events of the cell cycle. In CHEF/18 cells the three alkylated bases were able to induce aberrant metaphases and ana-telophases with different efficiency (70-100%). The effect was not dependent on the G1-S block and it was reversible even after cell commitment to DNA synthesis.

Induction of kinetochore-containing micronuclei by exogenous O6-methylguanine requires conversion of the methylated base to a nucleotide

It has been reported that exogenous alkylated purines, such as O6-methylguanine (O6meG), induce aneuploidy in mammalian cells. It is shown here that the aneugenic effect of O6meG, evidenced by its ability to induce micronuclei in rodent cells, is dependent on its conversion to O6-methyl-guanosine-5'-monophosphate (O6me-5'-GMP) by hypoxanthine-guanine phosphoribosyl transferase (HPRT). This conclusion, in contrast with previous in vitro data showing that O6meG does not seem to be a substrate for HPRT, was based on the following observations: 1) O6meG did not induce micronuclei in HPRT-deficient Chinese hamster cells, but did induce micronuclei in HPRT-proficient cells, and in mouse cells partially or totally deficient in adenine phosphoribosyl transferase; 2) O6meG was not metabolized in HPRT-deficient cells, while in wild-type cells a number of metabolites were detected by high performance liquid chromatography (HPLC) analysis of cold acid extracts, one of them coeluting with O6me-5'-GMP used as a marker; 3) when de novo synthesis of purine nucleotides was inhibited by aminopterin, O6meG sustained the growth of HPRT-proficient, but not of HPRT-deficient, cells; and 4) when HPRT-deficient cells were treated with liposomes charged with O6me-5'-GMP, induction of micronuclei was shown. The finding that methylated guanine exerts its aneugenic action through methylated nucleotide(s) provides an important, though indirect, support to the hypothesis that alkylating agents may induce aneuploidy via nucleotide pool alkylation.

Surface distribution and partition during freeze-fracture of CD8 antigens on human lymphocytes and on epithelial transfected cells

Freeze-fracture immunocytochemistry was used to analyse the surface distribution, redistribution induced by antibodies, and partition during freeze-fracture, of CD8 molecules on human T lymphocytes and rat epithelial transfected (FRT-U10) cells. Immunogold labelling of CD8 antigens was uniform over the unfractured cell surfaces of both lymphocytes and epithelial transfected cells. After freeze-fracture, the gold particles were associated with the exoplasmic outer leaflets of the plasma membranes in both cell types. In lymphocytes, incubation with antibodies at 37 degrees C up to 20 min induced patching and capping of the antigens on the unfractured cell surface. After fracture, the patched molecules appeared associated with the protoplasmic inner leaflet of the plasma membranes. Parallel antibody-treatment at 37 degrees C of FRT-U10 cells induced clustering of CD8 molecules but failed to cause further aggregation in larger patches or in caps. After freeze-fracture, the immunolabelling was clustered, but associated with the exoplasmic outer leaflet of the plasma membranes as in untreated cells. The different redistribution induced by antibodies and the different behaviour on fracture of the redistributed molecules in the two cell types may be regulated by CD8 interaction with the cytoskeleton.

Interactions of nuclear proteins from uninduced, induced and superinduced HeLa cells with metal regulatory elements MRE3 and 4 of the human metallothionein IIa-encoding gene

Transcriptional activation of metallothionein (MT)-encoding genes(MT) is regulated during heavy metal induction by short non-identical repeats, termed 'metal regulatory elements' (MRE), present in multiple imperfect copies in MT promoter regions of eukaryotes. Using mobility shift assays, we have studied the interaction between the human MRE 3 and 4 regions (hMRE3/4) of the MTIIa promoter and nuclear proteins from uninduced and Cd(2+)-induced HeLa cells, and from Cd(2+)-superinduced H454 cells, a HeLa-derived Cd(2+)-resistant cell isolate which overexpresses hMTIIa after exposure to metal. A specific complex with a similar electrophoretic mobility was formed in all three extracts. Dialysis of the extracts using EDTA inhibited the formation of the complexes, which could be reconstituted only after the addition of Zn2+. UV cross-linking analyses of the specific complexes formed by the three nuclear extracts interacting with the hMRE3/4 region revealed that in all of them polypeptides were present having similar electrophoretic mobilities and different molecular masses. Mobility shift assays showed no major differences in the binding of nuclear proteins from induced or uninduced cells. Proposed models of activation of metal-induced MT transcription are discussed.

Genotoxic effects of the carbamate insecticide methomyl. I. In vitro studies with pure compound and the technical formulation "Lannate 25"

The carbamate insecticide methomyl and the methomyl-containing technical formulation "Lannate 25" were tested on whole blood human lymphocyte cultures. Both products induced dose-dependent increases in chromosome aberrations and micronuclei. Lannate 25 induced DNA damage as measured by the alkaline elution assay and hydroxylation of guanine at the C8 position. Sister chromatid exchanges were not increased significantly with either product. Overall, the technical formulation was more active than the pure compound, when compared at similar concentrations of active principle. Moreover, a different ratio of CREST-positive/CREST-negative micronuclei was observed with the two products, pure methomyl being relatively more active than Lannate 25 in the induction of CREST-positive micronuclei. On the basis of these results, previous evaluations of methomyl as a nongenotoxic compound should be reconsidered.

A genotoxicity study on N-acryloyl-N'-phenylpiperazine: implications of aneugenic effects in risk evaluations

Further to a previous genotoxicity study, we analyzed sister-chromatid exchange (SCE) and DNA-repair induction (V79 and EUE cells in vitro) and DNA damage (rat liver in vivo) with regard to N-acryloyl-N'-phenylpiperazine (AcrNPP), a chemical proposed for biomaterial polymerization which contains an aromatic tertiary amine function in a piperazine cycle. This chemical induced SCEs in a dose-dependent fashion (up to approximately 3.7 times the control value), while it was negative for DNA-repair induction and weakly yet significantly positive for in vivo DNA damage (maximum increase approximately 1.4 times the control value). Taken together with our previous genotoxicity data on AcrNPP and structurally related compounds, the present results confirm that aneuploidy is a possible major effect of aromatic tertiary amines. As regards exposure to aneugenic agents, considerations on cancer risk evaluation are presented.

Chromosomes bearing amplified genes are a preferential target of chemicals inducing chromosome breakage and aneuploidy

Micronuclei were induced in V79 Chinese hamster cells and in PALA L and MTX M, two derivative cell lines harboring amplified genes, with 1,3-bis(2-chloroethyl)nitrosourea (BCNU) and vinblastine. Spontaneous and induced micronuclei were analyzed for the presence of centromeres by immunofluorescent CREST staining. Micronuclei formed in PALA L cells were also analyzed for the presence of amplified DNA by in situ hybridization with a CAD gene probe. Both cell lines containing amplified genes showed increased micronucleus induction by BCNU and vinblastine. The marker chromosome of PALA L cells was found to be a preferential target for both the clastogenic and the aneugenic action of the two chemicals. DNA amplification seems therefore to be a destabilizing factor of chromosomal structural integrity and mitotic segregation.

Genotoxicity analysis of N,N-dimethylaniline and N,N-dimethyl-p-toluidine

N,N-Dimethylaniline (DMA, CAS No. 121-69-7) and N,N-dimethyl-p-toluidine (DMPT, CAS No. 99-97-8) belong to the N-dialkylaminoaromatics, a chemical class structurally alerting to DNA reactivity. Their applications may be industrial (dye and pesticide intermediates, polymerizing agents) and surgical (polymerization accelerators for the manufacture of bone cements and prosthetic devices), thus implying heterogeneous types of human exposure. Findings of carcinogenicity in rodents and some nonexhaustive genotoxicity data are available for DMA, but to our knowledge no information is available on DMPT concerning either carcinogenicity or any kind of genetic toxicity. To investigate their mechanism of action and mutagenic/carcinogenic potential, DMA and DMPT were analyzed for complementary genotoxicity endpoints, namely, gene mutation in Salmonella (Ames test), structural and numerical chromosome aberrations in hamster V79 cells (micronucleus test, matched with an immunofluorescent staining for kinetochore proteins), and in vivo DNA damage in mouse and rat liver (alkaline DNA elution test). The results essentially indicate that both chemicals are chromosome damaging agents. Indeed, at the maximum nontoxic doses, they proved nonmutagenic in Salmonella (although their toxicity did not allow concentrations > 70 micrograms/plate to be tested) and weakly positive in inducing DNA damage (increases in DNA elution rates at most approximately 2.4 times control value). Conversely, they proved clearly positive in inducing numerical chromosome alterations, with dose-dependent increases up to more than five times the control value for DMPT. At the highest dose tested, both chemicals also showed a significant clastogenic effect.

Post-translational processing of an O-glycosylated protein, the human CD8 glycoprotein, during the intracellular transport to the plasma membrane

The biosynthesis of human CD8 glycoprotein in transfected rat epithelial cells produces an unglycosylated precursor, an intermediate species only initially O-glycosylated, and a doublet mature form carrying neutral and sialylated O-linked oligosaccharides with the core-2 structure (Pascale, M. C., Malagolini, N., Serafini-Cessi, F., Migliaccio, G., Leone, A., and Bonatti, S. (1992) J. Biol. Chem. 267, 9940-9947). In this study the most relevant post-translational events: dimerization, addition of the first O-linked GalNAc, fulfillment of O-linked chains, as well as expression of involved glycosyltransferases, have been examined and correlated with the localization and transit rate of CD8 through the exocytic pathway. The glycosyltransferase activities measured in rat epithelial cells transfected with human CD8 DNA are entirely consistent with the primary structure assigned to CD8 oligosaccharides. The half-time of appearance of the initially O-glycosylated precursor and mature form was estimated to be 4 and 14 min, respectively, and the half-time for delivery of mature CD8 to the cell surface was found to be about 30 min, indicating a very fast routing. Pulse experiments with [35S]cysteine at 37 degrees C followed by chase-periods at low temperatures showed that folding/dimerization occurs before routing to the Golgi apparatus, whereas the addiction of O-linked GalNAc appears to take place later, very likely in cis-Golgi cisternae. Treatment of cells with monensin accumulated the intermediate CD8 form carrying non-elongated O-linked GalNAc, whereas brefeldin A treatment produced a sialylated glycoprotein species with a mobility faster than the mature CD8. These results indicate that the two drugs affect assembly of O-linked chains at different time of their processing.