Repression of IFN-gamma induction of class II transactivator: a role for PRDM1/Blimp-1 in regulation of cytokine signaling

MHC class II is expressed in restricted lineages and is modulated in response to pathogens and inflammatory stimuli. This expression is controlled by MHC CIITA, which is transcribed from multiple promoters. Although factors required for induction of CIITA are well characterized, less is known about the mechanisms leading to repression of this gene. During plasma cell differentiation, B lymphocyte-induced maturation protein-1 (PRDM1/Blimp-1) represses promoter (p)III of CIITA, responsible for constitutive expression in B cells. pIV is inducible by IFN-gamma in epithelia, macrophages and B cells. An IFN regulatory factor-element (IRF-E) in CIITA-pIV, which is bound by IRF-1 and IRF-2, is necessary for this response. This site matches the PRDM1/Blimp-1 consensus binding site, and PRDM1/Blimp-1 is expressed in cell lineages in which this promoter is operative. We, therefore, investigated whether PRDM1 regulates CIITA-pIV and found that PRDM1 bound to CIITA-pIV in vivo and the IRF-E in vitro. PRDM1 repressed IFN-gamma-mediated induction of a CIITA-pIV luciferase reporter in a fashion dependent on an intact consensus sequence and competes with IRF-1/IRF-2 for binding to the IRF-E and promoter activation. In human myeloma cell lines that express IRFs, PRDM1 occupancy of CIITA-pIV was associated with resistance to IFN-gamma stimulation, while short interfering RNA knockdown of PRDM1 led to up-regulation of CIITA. Our data indicate that PRDM1 is a repressor of CIITA-pIV, identifying a target of particular relevance to macrophages and epithelia. These findings support a model in which PRDM1/Blimp-1 can modulate the cellular response to IFN-gamma by competing with IRF-1/IRF-2 dependent activation of target promoters.     

Condensation by DNA looping facilitates transfer of large DNA molecules into mammalian cells

Experimental studies of complete mammalian genes and other genetic domains are impeded by the difficulty of introducing large DNA molecules into cells in culture. Previously we have shown that GST–Z2, a protein that contains three zinc fingers and a proline-rich multimerization domain from the polydactyl zinc finger protein RIP60 fused to glutathione S-transferase (GST), mediates DNA binding and looping in vitro. Atomic force microscopy showed that GST–Z2 is able to condense 130–150 kb bacterial artificial chromosomes (BACs) into protein–DNA complexes containing multiple DNA loops. Condensation of the DNA loops onto the Z2 protein–BAC DNA core complexes with cationic lipid resulted in particles that were readily transferred into multiple cell types in culture. Transfer of total genomic linear DNA containing amplified DHFR genes into DHFR^– cells by GST–Z2 resulted in a 10-fold higher transformation rate than calcium phosphate co-precipitation. Chinese hamster ovarian cells transfected with a BAC containing the human TP53 gene locus expressed p53, showing native promoter elements are active after GST–Z2-mediated gene transfer. Because DNA condensation by GST–Z2 does not require the introduction of specific recognition sequences into the DNA substrate, condensation by the Z2 domain of RIP60 may be used in conjunction with a variety of other agents to provide a flexible and efficient non-viral platform for the delivery of large genes into mammalian cells.     

Over-Expression in <Emphasis Type="Italic">E. coli</Emphasis> and Purification of the Human OCTN2 Transport Protein

The OCTN2 cDNA amplified from human skin fibroblast was cloned in pET-41a(+) carrying the glutathione S-transferase (GST) gene. The construct pET-41a(+)–hOCTN2 was used to express the GST–hOCTN2 fusion protein in Escherichia coli Rosetta(DE3)pLysS. The best over-expression was obtained after 6 h of induction with IPTG at 28°C. The GST–hOCTN2 polypeptide was collected in the inclusion bodies and showed an apparent molecular mass on SDS-PAGE of 85 kDa. After solubilization with a buffer containing 0.8% sarkosyl and 3 M urea, the fusion protein was applied onto a Ni²⁺-chelating chromatography column. The purified GST–hOCTN2 was treated with thrombin, and the hOCTN2 was separated from the GST by size exclusion chromatography. After the whole procedure, a yield of about 0.2 mg purified protein per liter of cell culture was obtained. To improve the protein yield, hOCTN2 cDNA was subjected to codon bias. The second codon CGG was substituted with AAA; the substitution led to the mutation R2K in the hOCTN2 protein. hOCTN2(R2K) cDNA was cloned in pET-21a(+) carrying a C-terminal 6His tag. The resulting protein was expressed in E. coli Rosetta(DE3)pLysS and purified by Ni²⁺-chelating chromatography. A yield of about 3.5 mg purified protein per liter of cell culture was obtained with this procedure.     

Laryngeal and oropharyngeal cancer, and alcohol dehydrogenase 3 and glutathione S-transferase M1 polymorphisms

In this study the GSTμ phenotype and ADH genotype at the ADH3 locus were investigated in a group of 39 alcoholic men with upper respiratory/digestive tract cancer: 21 with oropharyngeal cancer and 18 with laryngeal cancer. The results are compared with those of a control group of 37 alcoholic men without alcohol-related medical complications. Of the control subjects, 48% were found to be GSTμ deficient [GSTμ(–)] and 19% carried the ADH₃ ¹/ADH₃ ¹ genotype. In the laryngeal cancer patients, a significantly elevated frequency of both the GSTμ(–) (78%) and ADH₃ ¹/ADH₃ ¹ genotype (56%) was observed, relative to the control group. On the basis of this result, the risk of laryngeal cancer associated with the GSTμ(–) and ADH₃ ¹/ ADH₃ ¹ genotypic combination within the population of alcoholics was estimated to be 12.9 with a 95% confidence interval of 1.8–92 (P < 0.01) relative to alcoholic individuals who have GSTμ [GSTμ(+)] and are not ADH₃ ¹/ADH₃ ¹. Thus, alcoholics who are GSTμ(–) and ADH₃ ¹/ADH₃ ¹ have at least an 80% greater risk of developing laryngeal cancer than alcoholics who are GSTμ(+) and who are not ADH₃ ¹/ ADH₃ ¹. In addition, the oropharyngeal cancer patients had excess frequencies of both GSTμ(–) (62%) and ADH₃ ¹/ ADH₃ ¹ (43%) relative to the control group, but these excess frequencies were not statistically significant. The GSTμ(–) and ADH₃ ¹/ADH₃ ¹ genotypic combination may be a constitutional risk factor for laryngeal cancer among alcoholics. Received: 5 July 1996 / Revised: 15 October 1996     

A modified hepatitis B surface antigen carrying both preS1 and preS2 epitopes

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