[Genetic complementation group analysis of xeroderma pigmentosum patients in China]

OBJECTIVE

To establish skin fibroblast cell strains derived from Chinese xeroderma pigmentosum(XP) patients and to analyze the genetic complementation group and distribution.

METHODS

From four XP patients, skin fibroblast cell strains were derived and used for the complementation group analysis by autoradiography and cell-fusion technique.

RESULTS

Of the four XP patients from apparently independent families, three were assigned to group C, and one belonged to group E. This is the first report on XP-E patient in China.

CONCLUSION

Based on the data from the previous 7 cases and the present 4 cases, the distribution of complementation group in Chinese XP patients known at present is: nine XP-C, one XP-F and one XP-E. Although the number of cases is still limited, XP-C appears to be more frequent in China. This forms a marked contrast to Japanese XP patients, who are dominated by XP-A with infrequent presence of XP-C.

Tricyclopropylamine and Its Radical Cation

A surprisingly high first vertical ionization energy (8.44 eV) and an unusually high oxidation potential are exibited by tricyclopropylamine (1)-in sharp contrast to triisopropylamine. These are attributed to the near-tetrahedral geometry of 1 at the N atom and the perpendicular orientation-with respect to the N-orbital axis-of the cyclopropyl groups. gamma-Irradiation of 1 led to the radical cation 1(.)(+), which, in accord with computations, has a planar C(3h)-symmetrical structure. The EPR-spectroscopic and computational results disclose a dramatic, previously not reported, conformational change on going from 1 to 1(.)(+).

Renal proximal tubular AT2 receptor: signaling and transport

Previous studies have documented that the vasoactive agonist angiotensin II (AngII) directly affects proximal tubular sodium-bicarbonate reabsorption in a biphasic manner, whereby picomolar concentrations promote reabsorption and nanomolar concentrations have the converse effect. Although it is generally agreed that the AT1 receptor subtype mediates AngII-induced sodium-bicarbonate reabsorption primarily through adenylate cyclase, the receptor subtype mediating natriuresis is less well defined. Using mouse proximal tubular cells, this study documents AT1-dependent enhancement (candesartan-inhibitable) of bicarbonate reabsorption and AT2-induced (PD123319- and CGP42112A-inhibitable) decrement of bicarbonate absorption. The signaling mechanisms were examined in rabbit proximal tubule cells in culture. The AT2 signaling involves G protein beta- and gamma-mediated phospholipase A2 activation, arachidonic acid release, and downstream events linked to Shc/Grb2/Sos and p21ras rather than protein kinase C as reported previously for AngII receptors. These observations provide a novel mechanism for AngII-AT2 receptor-mediated transport modulation.

[Cytogenetic study in eight cases of Fanconi anemia]

OBJECTIVE

To study the clinical, hematological and cytogenetical characteristics in Fanconi anemia (FA).

METHODS

Culture the peripheral lymphocytes with Mitomycin C (MMC) induction to count the chromosome breakages and to count the sister chromatid exchanges (SCE) in FA.

RESULTS

The clinical and hematological manifestations in FA varied at all. Spontaneous chromosome break and MMC induced break in FA were significantly higher than those in normal. Spontaneous and induced SCE were also higher in FA.

CONCLUSION

Owing to genetic heterogeneity in FA, the phenotypes in FA are diversified also. So, chromosome breakage study is a very important method in the diagnosis of FA, and gene complementation analysis may identify which complementation group the patient carries.

SHP-1 deficiency in B-lineage cells is associated with heightened lyn protein expression and increased lyn kinase activity

SHP-1 protein tyrosine phosphatase is a critical regulator of signal transduction in hematopoietic cells. In the present study, we derived two pre-B cell lines, PBCL-1 and PBCL-2, from normal and SHP-1-deficient motheaten mice, respectively, and characterized hyperphosphorylated proteins in PBCL-2 cells to identify SHP-1-regulated molecules. Two proteins of 56 and 53 kDa (p56/p53) in PBCL-2 cells showed heightened phosphorylation (3- to 6-fold) in comparison with those in PBCL-1. p56/p53 were identified as the two forms of the lyn protein tyrosine kinase (p56/p53lyn), which showed increased kinase activity in PBCL-2 cells. Interestingly, the protein levels of p56/53lyn were found to be 3- to 6-fold higher in PBCL-2 cells than those in PBCL-1, whereas the transcript levels of lyn in the two cell lines were comparable. A modest increase in p56/53lyn protein expression was also detected in primary spleen B cells of motheaten mice. Thus SHP-1 deficiency in B-lineage cells, especially pre-B cells, is associated with increased lyn protein expression and kinase activity. These data indicate a role for SHP-1 in regulating lyn through a post-transcriptional mechanism.

Arachidonic acid mediates angiotensin II effects on p21ras in renal proximal tubular cells via the tyrosine kinase-Shc-Grb2-Sos pathway

In kidney epithelial cells, an angiotensin II (Ang II) type 2 receptor subtype (AT2) is linked to a membrane-associated phospholipase A2 (PLA2) and the mitogen-activated protein kinase (MAPK) superfamily. However, the intervening steps in this linkage have not been determined. The aim of this study was to determine whether arachidonic acid mediates Ang II's effect on p21ras and if so, to ascertain the signaling mechanism(s). We observed that Ang II activated p21ras and that mepacrine, a phospholipase A2 inhibitor, blocked this effect. This activation was also inhibited by PD123319, an AT2 receptor antagonist but not by losartan, an AT1 receptor antagonist. Furthermore, Ang II caused rapid tyrosine phosphorylation of Shc and its association with Grb2. Arachidonic acid and linoleic acid mimicked Ang II-induced tyrosine phosphorylation of Shc and activation of p21ras. Moreover, Ang II and arachidonic acid induced an association between p21ras and Shc. We demonstrate that arachidonic acid mediates linkage of a G protein-coupled receptor to p21ras via Shc tyrosine phosphorylation and association with Grb2/Sos. These observations have important implications for other G protein-coupled receptors linked to a variety of phospholipases.

Interaction between the pili of Pseudomonas aeruginosa PAK and its carbohydrate receptor beta-D-GalNAc(1-->4)beta-D-Gal analogs

Pseudomonas aeruginosa employs pili to mediate adherence to epithelial cell surface receptors. Previously, it has been shown that the pilus adhesin of P. aeruginosa PAK binds to the ganglioside asialo-GM1. In particular, it was found that the carbohydrate sequence beta-D-GalNAc(1-->4)beta-D-Gal is the minimal carbohydrate receptor sequence of asialo-GM1. To study the binding specificity of P. aeruginosa, O-modified and N-modified sugar analogs, where each hydroxyl group was substituted either by O-methyl or O-propyl and the acetamido group was changed to a propionamido group, were synthesized. The sugar analogs were evaluated as inhibitors in a competitive solid phase binding assay. The results demonstrate that the pili of P. aeruginosa PAK accepts a variety of sugar analogs possessing the sequence beta-D-GalNAc(1-->4)beta-D-Gal. Most sugar analogs bind with a similar order of magnitude (50% inhibitory concentration (IC50) = 60-130 microM) except for the 2-O-propyl derivative 7 (IC50 = 8 +/- 4 microM) compared with an IC50 of 79 +/- 18 microM for the native compound. The significant increase in binding affinity of 2-O-propyl derivative 7 suggests that improved inhibitors of adhesion may be prepared by introducing a hydrophobic side chain at the 2-position of galactose.

Reduced Tyk2/SHP-1 interaction and lack of SHP-1 mutation in a kindred of familial hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHLH) is an autosomal recessive disease with features similar to those of the murine motheaten phenotype resulting from mutations of protein tyrosine phosphatase SHP-1. This has raised the possibility that defects in SHP-1 or SHP-1-regulated signaling molecules may be present in FHLH. In this study, we examined SHP-1 protein and transcript in the peripheral blood mononuclear cells (PBMC) of an FHLH family. Our results show that the FHLH patient and the parents express comparable levels of a single SHP-1 protein and that the SHP-1 cDNA clone from the patient contains no mutation in the coding region. Interestingly, a reduced association of SHP-1 with the Jak family kinase Tyk2 was detected in the patient and the defect appears to have been inherited from one of the parents. This reduced SHP-1/Tyk2 association is likely due to a defect in Tyk2 or in cellular factors regulating Tyk2, because we found no abnormalities in SHP-1 or in SHP-1 association with the other Jak kinases. These data demonstrate that the SHP-1 gene is intact in FHLH and that the defect in some cases with this disease may involve signaling molecules regulated by SHP-1.

Macrophages from motheaten and viable motheaten mutant mice show increased proliferative responses to GM-CSF: detection of potential HCP substrates in GM-CSF signal transduction

Loss of functional hematopoietic cell phosphatase (HCP) underlies severe hematopoietic and immunologic abnormalities in mice homozygous for the motheaten and viable motheaten mutations. These mice die from pulmonary accumulation of macrophages that are regulated by macrophage colony-stimulating factor (M-CSF) and granulocyte (G)-M-CSF. We determined the growth response of motheaten macrophages to the two growth factors and looked for potential HCP substrates in these cells. Motheaten macrophages showed increased proliferative responses to GM-CSF but not to M-CSF, demonstrating that HCP plays a critical role in downregulating GM-CSF mitogenic signaling. Despite the heightened growth responses of the motheaten macrophages to GM-CSF, there were no marked differences between motheaten macrophages and normal controls in GM-CSF-induced phosphorylation of GM-CSFR beta, Jak2, STAT5 and MAPK, indicating that these molecules are not major HCP substrates in GM-CSF signaling. Interestingly, several markedly hyperphosphorylated proteins were detected in the motheaten macrophages, including a novel 126-kDa phosphotyrosine protein that associated with the phosphatase via its SH2 domains, suggesting that these proteins depend on HCP for dephosphorylation and may mediate the heightened growth responses to GM-CSF. Our data indicate that macrophage hypersensitivity to GM-CSF may be a major factor in motheaten pathogenesis and that HCP may dephosphorylate novel substrates critical in GM-CSF mitogenic signaling.

Direct association with and dephosphorylation of Jak2 kinase by the SH2-domain-containing protein tyrosine phosphatase SHP-1

SHP-1 is an SH2-containing cytoplasmic tyrosine phosphatase that is widely distributed in cells of the hematopoietic system. SHP-1 plays an important role in the signal transduction of many cytokine receptors, including the receptor for erythropoietin, by associating via its SH2 domains to the receptors and dephosphorylating key substrates. Recent studies have suggested that SHP-1 regulates the function of Jak family tyrosine kinases, as shown by its constitutive association with the Tyk2 kinase and the hyperphosphorylation of Jak kinases in the motheaten cells that lack functional SHP-1. We have examined the interactions of SHP-1 with two tyrosine kinases activated during engagement of the erythropoietin receptor, the Janus family kinase Jak-2 and the c-fps/fes kinase. Immunoblotting studies with extracts from mouse hematopoietic cells demonstrated that Jak2, but not c-fes, was present in anti-SHP-1 immunoprecipitates, suggesting that SHP-1 selectively associates with Jak2 in vivo. Consistent with this, when SHP-1 was coexpressed with these kinases in Cos-7 cells, it associated with and dephosphorylated Jak2 but not c-fes. Transient cotransfection of truncated forms of SHP-1 with Jak2 demonstrated that the SHP-1-Jak2 interaction is direct and is mediated by a novel binding activity present in the N terminus of SHP-1, independently of SH2 domain-phosphotyrosine interaction. Such SHP-1-Jak2 interaction resulted in induction of the enzymatic activity of the phosphatase in in vitro protein tyrosine phosphatase assays. Interestingly, association of the SH2n domain of SHP-1 with the tyrosine phosphorylated erythropoietin receptor modestly potentiated but was not essential for SHP-1-mediated dephosphorylation of Jak2 and had no effect on c-fes phosphorylation. These data indicate that the main mechanism for regulation of Jak2 phosphorylation by SHP-1 involves a direct, SH2-independent interaction with Jak2 and suggest the existence of similar mechanisms for other members of the Jak family of kinases. They also suggest that such interactions may provide one of the mechanisms that control SHP-1 substrate specificity.

Genetic analysis of non-insulin dependent diabetes mellitus in the GK rat

Non-insulin dependent diabetes mellitus (NIDDM) is a major public health problem, but its aetiology remains poorly understood. We have performed a comprehensive study of the genetic basis of diabetes in the Goto-Kakizaki (GK) rat, the most widely used animal model of non-obese NIDDM. The genetic dissection of NIDDM using this model has allowed us to map three independent loci involved in the disease. In addition, we identify a major factor affecting body weight, but not glucose tolerance, on chromosome 7 and map a further 10 regions that are suggestive for linkage. We conclude that NIDDM is polygenic and fasting hyperglycaemia and postprandial hyperglycaemia clearly have distinct genetic bases.

Phosphorylation of tyrosine 503 in the erythropoietin receptor (EpR) is essential for binding the P85 subunit of phosphatidylinositol (PI) 3-kinase and for EpR-associated PI 3-kinase activity

We recently reported that phosphatidylinositol (PI) 3-kinase becomes associated with the activated erythropoietin receptor (EpR), most likely through the Src homology 2 (SH2) domains within the p85 subunit of PI-3 kinase and one or more phosphorylated tyrosines within the EpR. We have now investigated this interaction in more detail and have found, based on both blotting studies with glutathione S-transferase-p85-SH2 fusion proteins and binding of these fusion proteins to SDS-denatured EpRs, that this binding is direct. Moreover, both in vitro competition studies, involving phosphorylated peptides corresponding to the amino acid sequences flanking the eight tyrosines within the intracellular domain of the EpR, and in vivo studies with mutant EpRs bearing tyrosine to phenylalanine substitutions, indicate that phosphorylation of Tyr503 within the EpR is essential for the binding of PI 3-kinase. The presence of PI 3-kinase activity in EpR immunoprecipitates from DA-3 cells infected with wild-type but not Y503F EpRs confirms this finding. Our results demonstrate that the SH2 domains of p85 can bind, in addition to their well established Tyr-Met/Val-X-Met consensus binding sequence, a Tyr-Val-Ala-Cys motif that is present in the EpR. A comparison of erythropoietin-induced tyrosine phosphorylations and proliferation of wild-type and Y503F EpR-infected DA-3 cells revealed no differences. However, the PI-3 kinase inhibitor, wortmannin, markedly inhibited the erythropoietin-induced proliferation of both cell types, suggesting that PI 3-kinase is activated in Y503F EpR expressing cells. This was confirmed by carrying out PI 3-kinase assays with anti-phosphotyrosine immunoprecipitates from erythropoietin-stimulated Y503F EpR-infected DA-3 cells and suggested that PI 3-kinase has a role in regulating erythropoietin-induced proliferation, but at a site distinct from the EpR.

Association of the interferon-dependent tyrosine kinase Tyk-2 with the hematopoietic cell phosphatase

The tyrosine kinase Tyk-2 is physically associated with the Type I interferon (IFN) receptor complex and is rapidly activated during IFN alpha stimulation. We report that Tyk-2 forms stable complexes with the SH2-containing hematopoietic cell phosphatase (HCP) in several hematopoietic cell lines in vivo, and that the IFN alpha-induced tyrosine-phosphorylated form of Tyk-2 is a substrate for the phosphatase activity of HCP in in vitro assays. Furthermore, treatment of cells with the phosphatase inhibitor sodium orthovanadate induces tyrosine phosphorylation of Tyk-2 and an associated 115-kDa protein. Altogether, these data suggest that HCP regulates tyrosine phosphorylation of the Tyk-2 kinase, and thus its function may be important in the transmission of signals generated at the Type I IFN receptor level.

Differential macrophage-mediated cytotoxicity to P388 leukemia cells and its drug-resistant cells examined by a new MTT assay

After activation by interferon-gamma (INF-gamma) and lipopolysaccharide(LPS), mouse peritoneal macrophages were cocultured with P388 parental cell line (P388/PRT) and its adriamycin (ADM)-, cisplatin(CDDP)-, cyclophosphamide(CPM)-, and mitomycin-C(MMC)-resistant cell lines for one day at effector:target ratios (E:T) of 10:1, 5:1, and 2:1. The direct 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) cleavage assay and a new indirect MTT assay as well as clonogenic assay were used to quantitate activated macrophage-mediated cytotoxicity to these non-adherent leukemia targets. The results revealed that all the P388 cell lines can be suppressed efficiently by activated macrophages, but P388 CPM- and MMC-resistant cell lines (P388/CPM, P388/MMC) were more susceptible than P388/PRT while P388 ADM- and CDDP-resistant cell lines (P388/ADM, P388/CDDP) shared equal level of survival rates with P388/PRT. This study also showed that both non-activated and activated macrophages can produce formazan in a high level, which can interfere with the final results of direct MTT assay. The new indirect MTT assay can avoid such interference by separating the effectors from the targets before performing the MTT assay and reflects the real viability of the targets so the indirect MTT assay developed in this study could be a better way to examine cytostatic and cytotoxic effect of activated macrophages on non-adherent tumor cells in vitro.

Antitumor activity of siwenmycin: a novel anthracycline antibiotic

A novel anthracycline antibiotic, siwenmycin, isolated from the culture of Streptomyces galilaeus var. siwenesis, was examined for its antitumor activities against P388, K562, B16-F10, HeLa, HEp-2 and Lewis lung carcinoma cell lines. The results showed that siwenmycin was effective against P388, K562, HeLa and HEp-2 tumor cell lines in vitro, and significantly inhibited the growth of the Lewis lung carcinoma cell line in vivo. Siwenmycin could also suppress spontaneous and artificial pulmonary metastases of B16-F10 and Lewis lung carcinoma cell lines in C57BL/6 mice. The inhibitory effect of siwenmycin on spontaneous pulmonary metastasis of Lewis lung carcinoma in C57BL/6 mice was even stronger than that of adriamycin (ADM), which is, at present, commonly used in clinical practice. Furthermore, the double-labeling test used in this study has verified that siwenmycin can inhibit cellular RNA synthesis at about one tenth the concentration required to inhibit DNA synthesis to the same degree, indicating that the antitumor mechanism of siwenmycin also differs from that of ADM. The acute toxicity of siwenmycin was very low, and it was as effective in vivo as in vitro, suggesting that this newly found antibiotic should be studied for possible clinical antitumor applications.

A new 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for testing macrophage cytotoxicity to L1210 and its drug-resistant cell lines in vitro

Activated by interferon gamma (IFN gamma)(50 U/ml) and lipopolysaccharide (50 ng/ml), mouse peritoneal macrophages were cocultured with the L1210 parental cell line (L1210/PRT) and its Adriamycin-, cisplatin-resistant cell lines (L1210/ADM, L1210/CDDP) for 24 h at effector: target (E:T) ratios of 10:1, 5:1 and 2:1. The direct 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide (MTT)-cleavage assay, a new improved indirect MTT assay, and the colony-formation assay were used to quantify macrophage-mediated suppression of these non-adherent tumour targets. The results showed that the macrophages can produce formazan at a high level, which can interfere with the final results of a direct MTT assay. The new indirect MTT assay can avoid such interference because the effectors are separated from the targets before the assay is performed, so the real viability of the targets is reflected. An indirect MTT assay, as developed in this study, could be better than the direct assay for examining the suppressive effect of activated macrophages on non-adherent tumour cells in vitro. This study also revealed that all the L1210 cell lines can be suppressed significantly by the macrophages at E:T ratios of 10:1 and 5:1 while the two drug-resistant cell lines have lower survival rates at an E:T ratio of 10:1, indicating that they are more susceptible than their parental cell line.