Expression of CD175 (Tn), CD175s (sialosyl-Tn) and CD176 (Thomsen-Friedenreich antigen) on malignant human hematopoietic cells.

The expression of the histo-blood group carbohydrate structures T-nouvelle (Tn, CD175), sialylated Tn (CD175s) and the Thomsen-Friedenreich disaccharide (TF, CD176) on human leukemia cell lines was analyzed by their reactivity with specific monoclonal antibodies in flow cytometry, immunohistology and immunoprecipitation. Expression of sialylated CD176 was evaluated by comparative immunostaining with anti-CD176 antibodies before and after sialidase treatment. While only few cell lines expressed unmasked CD176, sialylated CD176 was present on all hematopoietic cell lines and native lymphocytes examined. CD175 and CD175s are preferentially expressed on erythroblastic leukemia cell lines. CD175s expression in these cells is consistent with the transcription of the gene encoding the key enzyme alpha2,6-sialyltransferase (hST6GalNAc1). The staining intensity was reduced after methanol pretreatment of cells, indicating that these glycans are partially expressed as constituents of glycosphingolipids. Immunoprecipitation and subsequent Western blotting revealed a series of distinct high molecular glycoproteins as carriers for these carbohydrate antigens. CD34 was identified as major carrier of CD176 by immunoprecipitation and microsequencing on a KG-1 subline enriched for CD176 expression. Incubation of several CD176-positive cell lines with anti-CD176 antibodies induced apoptosis of these cells, an effect not observed with anti-CD175/CD175s antibodies. Since the presence of naturally occurring anti-CD176 antibodies may represent a mechanism of immunosurveillance against CD176-positive tumor cells, we propose that sialylation of surface-expressed CD176--among other functions--protects against apoptosis.

Antiribosomal-P autoantibodies from psychiatric lupus target a novel neuronal surface protein causing calcium influx and apoptosis.

The interesting observation was made 20 years ago that psychotic manifestations in patients with systemic lupus erythematosus are associated with the production of antiribosomal-P protein (anti-P) autoantibodies. Since then, the pathogenic role of anti-P antibodies has attracted considerable attention, giving rise to long-term controversies as evidence has either contradicted or confirmed their clinical association with lupus psychosis. Furthermore, a plausible mechanism supporting an anti-P-mediated neuronal dysfunction is still lacking. We show that anti-P antibodies recognize a new integral membrane protein of the neuronal cell surface. In the brain, this neuronal surface P antigen (NSPA) is preferentially distributed in areas involved in memory, cognition, and emotion. When added to brain cellular cultures, anti-P antibodies caused a rapid and sustained increase in calcium influx in neurons, resulting in apoptotic cell death. In contrast, astrocytes, which do not express NSPA, were not affected. Injection of anti-P antibodies into the brain of living rats also triggered neuronal death by apoptosis. These results demonstrate a neuropathogenic potential of anti-P antibodies and contribute a mechanistic basis for psychiatric lupus. They also provide a molecular target for future exploration of this and other psychiatric diseases.

Caspase-dependent regulation and subcellular redistribution of the transcriptional modulator YY1 during apoptosis.

The transcriptional regulator Yin Yang 1 (YY1) controls many aspects of cell behavior and is essential for development. We analyzed the fate of YY1 during apoptosis and studied the functional consequences. We observed that this factor is rapidly translocated into the cell nucleus in response to various apoptotic stimuli, including activation of Fas, stimulation by tumor necrosis factor, and staurosporine and etoposide treatment. Furthermore, YY1 is cleaved by caspases in vitro and in vivo at two distinct sites, IATD(12)G and DDSD(119)G, resulting in the deletion of the first 119 amino acids early in the apoptotic process. This activity generates an N-terminally truncated YY1 fragment (YY1Delta119) that has lost its transactivation domain but retains its DNA binding domain. Indeed, YY1Delta119 is no longer able to stimulate gene transcription but interacts with DNA. YY1Delta119 but not the wild-type protein or the caspase-resistant mutant YY1D12A/D119A enhances Fas-induced apoptosis, suggesting that YY1 is involved in a positive feedback loop during apoptosis. Our findings provide evidence for a new mode of regulation of YY1 and define a novel aspect of the involvement of YY1 in the apoptotic process.

PARP-10, a novel Myc-interacting protein with poly(ADP-ribose) polymerase activity, inhibits transformation.

The proto-oncoprotein c-Myc functions as a transcriptional regulator that controls different aspects of cell behavior, including proliferation, differentiation, and apoptosis. In addition, Myc proteins have the potential to transform cells and are deregulated in the majority of human cancers. Several Myc-interacting factors have been described that mediate part of Myc's functions in the control of cell behavior. Here, we describe the isolation of a novel 150 kDa protein, designated PARP-10, that interacts with Myc. PARP-10 possesses domains with homology to RNA recognition motifs and to poly(ADP-ribose) polymerases (PARP). Molecular modeling and biochemical analysis define a PARP domain that is capable of ADP-ribosylating PARP-10 itself and core histones, but neither Myc nor Max. PARP-10 is localized to the nuclear and cytoplasmic compartments that is controlled at least in part by a Leu-rich nuclear export sequence (NES). Functionally, PARP-10 inhibits c-Myc- and E1A-mediated cotransformation of rat embryo fibroblasts, a function that is independent of PARP activity but that depends on a functional NES. Together, our findings define a novel PARP enzyme involved in the control of cell proliferation.

Sulfur oxidation in Paracoccus pantotrophus: interaction of the sulfur-binding protein SoxYZ with the dimanganese SoxB protein.

The central protein of the sulfur-oxidizing enzyme system of Paracoccus pantotrophus, SoxYZ, formed complexes with subunits associated and covalently bound. In denaturing SDS-polyacrylamide gel electrophoresis (PAGE) SoxY migrated at 12 and SoxZ at 16kDa. SDS-PAGE of homogeneous SoxYZ without reductant separated dimeric complexes of 25, 29, and 32kDa identified by the N-terminal amino acid sequences as SoxY-Y, SoxY-Z, and SoxZ-Z, and subunit cleavage by reduction suggested their linkage via protein disulfide bonds. SoxYZ was reversibly redox active between -0.25 and 0.2V, as monitored by a combined electrochemical and FTIR spectroscopic approach. The dimanganese SoxB protein (58.611Da) converted the covalently linked heterodimer SoxY-Z to SoxYZ with associated subunits which in turn aggregated to the heterotetramer Sox(YZ)(2). This reaction depended on time and the SoxB concentration, and demonstrated the interaction of these two Sox proteins.

Nucleolin as activator of human papillomavirus type 18 oncogene transcription in cervical cancer.

High risk human papillomaviruses (HPVs) are central to the development of cervical cancer and the deregulated expression of high risk HPV oncogenes is a critical event in this process. Here, we find that the cell protein nucleolin binds in a sequence-specific manner to the HPV18 enhancer. The DNA binding activity of nucleolin is primarily S phase specific, much like the transcription of the E6 and E7 oncoproteins of HPV18 in cervical cancer cells. Antisense inactivation of nucleolin blocks E6 and E7 oncogene transcription and selectively decreases HPV18(+) cervical cancer cell growth. Furthermore, nucleolin controls the chromatin structure of the HPV18 enhancer. In contrast, HPV16 oncogene transcription and proliferation rates of HPV16(+) SiHa cervical cancer cells are independent of nucleolin activity. Moreover, nucleolin expression is altered in HPV18(+) precancerous and cancerous tissue from the cervix uteri. Whereas nucleolin was homogeneously distributed in the nuclei of normal epithelial cells, it showed a speckled nuclear phenotype in HPV18(+) carcinomas. Thus, the host cell protein nucleolin is directly linked to HPV18-induced cervical carcinogenesis.

EcoRII: a restriction enzyme evolving recombination functions?

The restriction endonuclease EcoRII requires the cooperative interaction with two copies of the sequence 5'CCWGG for DNA cleavage. We found by limited proteolysis that EcoRII has a two-domain structure that enables this particular mode of protein-DNA interaction. The C-terminal domain is a new restriction endonuclease, EcoRII-C. In contrast to the wild-type enzyme, EcoRII-C cleaves DNA specifically at single 5'CCWGG sites. Moreover, substrates containing two or more cooperative 5'CCWGG sites are cleaved much more efficiently by EcoRII-C than by EcoRII. The N-terminal domain binds DNA specifically and attenuates the activity of EcoRII by making the enzyme dependent on a second 5'CCWGG site. Therefore, we suggest that a precursor EcoRII endonuclease acquired an additional DNA-binding domain to enable the interaction with two 5'CCWGG sites. The current EcoRII molecule could be an evolutionary intermediate between a site-specific endonuclease and a protein that functions specifically with two DNA sites such as recombinases and transposases. The combination of these functions may enable EcoRII to accomplish its own propagation similarly to transposons.

Intermolecular electron transfer in cytochrome P450cam covalently bound with Tris(2,2'-bipyridyl)ruthenium(II): structural changes detected by FTIR spectroscopy.

Using Fourier transform infrared spectroscopy (FTIR) we have monitored the changes in the protein structure following photoinduced electron transfer from Ru(bpy)(3)(2+) covalently attached to cysteine 334 on the surface of cytochrome P450cam (CYP101). The FTIR difference spectra between the oxidized and reduced form indicate changes in a salt link and the secondary structure (alpha-helix and turn regions). Photoreduction was carried out in the presence of carbon monoxide in order to prove the reduction of the heme iron by means of the appearance of the characteristic CO stretch vibration infrared band at 1940 cm(-1) for the camphor-bound protein. This infrared band has also been used to estimate electron transfer rates. The observed rates depend on the protein concentration, indicating that intermolecular electron transfer occurs between the labeled molecules.

Asymmetric photocross-linking pattern of restriction endonuclease EcoRII to the DNA recognition sequence.

The EcoRII homodimer engages two of its recognition sequences (5'-CCWGG) simultaneously and is therefore a type IIE restriction endonuclease. To identify the amino acids of EcoRII that interact specifically with the recognition sequence, we photocross-linked EcoRII with oligonucleotide substrates that contained only one recognition sequence for EcoRII. In this recognition sequence, we substituted either 5-iododeoxycytidine for each C or 5-iododeoxyuridine for A, G, or T. These iodo-pyrimidine bases were excited using a UV laser to result in covalent cross-linking products. The yield of EcoRII photocross-linked to the 5'-C of the 5'-CCAGG strand of the recognition sequence was 45%. However, we could not photocross-link EcoRII to the 5'-C of the 5'-CCTGG strand. Thus, the contact of EcoRII to the bases of the recognition sequence appears to be asymmetric, unlike that expected for most type II restriction endonucleases. Tryptic digestion of free and of cross-linked EcoRII, followed by high performance liquid chromatography (HPLC) separation of the individual peptides and Edman degradation, identified amino acids 25-49 of EcoRII as the cross-linking peptide. Mutational analysis of the electron-rich amino acids His(36) and Tyr(41) of this peptide indicates that Tyr(41) is the amino acid involved in the cross-link and that it therefore contributes to specific DNA recognition by EcoRII.