小麦背景中簇毛麦6V染色体的遗传稳定性及其在配子中的传递

小麦－簇毛麦６Ｖ二体附加系,６Ａ（６Ｖ）二体代换系,６Ａ＾Ｌ．６Ｖ＾ｓ二体易位系在细胞学上是基本稳定的６Ｖ,６Ａ＾Ｌ．６Ｖ＾ｓ染色体能够通过配子稳定地传递给后代,在杂合状态下,带有６Ｖ的配子传递率普遍显著下降,在单体附加系（２１”Ｗ＋６Ｖ）中,６Ｖ通过雌配子的传递率（１１．３％）高于通过雄配子的传递率（５．９％）,在单体代换系（２０”Ｗ＋６Ａ－６Ｖ）中,６Ｖ通过雌配子的传递率（１０．４％）低于通过     

高等植物葡萄糖-6-磷酸脱氢酶与6-磷酸葡萄糖酸脱氢酶基因的不同进化起源

葡萄糖-6-磷酸脱氢酶与6-磷酸葡萄糖酸脱氢酶是植物戊糖磷酸途径中的两个酶.在克隆了水稻质体葡萄糖-6-磷酸脱氢酶基因OsG6PDH2和质体6-磷酸葡萄糖脱氢酶基因Os6PGDH2基础上,分析比较了水稻胞质和质体葡萄糖-6-磷酸脱氢酶基因和6-磷酸葡萄糖酸脱氢酶基因的基因结构、表达特性和进化地位.结合双子叶模式植物拟南芥两种酶基因的分析结果,认为高等植物葡萄糖-6-磷酸脱氢酶基因和6-磷酸葡萄糖酸脱氢酶基因在进化方式上截然不同,葡萄糖-6-磷酸脱氢酶的胞质基因与动物和真菌等真核生物具有共同的祖先;6-磷酸葡萄糖酸脱氢酶的胞质酶和质体酶基因都起源于原核生物的内共生.讨论了植物葡萄糖-6-磷酸脱氢酶与6-磷酸葡萄糖酸脱氢酶基因可能的进化模式,为高等植物及质体的进化起源提供了新的资料.     

补体第六成分（C6）在汉族5个群体中的多态分布

用聚丙烯酰胺等电聚焦技术和免疫酶标法,调查分析了汉族5个群体补体第六成分(C6)的遗传多态性,得出基因频率如下。郑州汉族:C6*A 0.4521、C6*B 0.5228、C6*B_2 0.0183、和C6*R 0.0068。兰州汉族:C6*A 0.4612、C6*B 0.5218和C6*B_2 0.0170。呼和浩特汉族:C6*A 0.4452、C6*B 0.5286、C6*B_2 0.0214和C6*R 0.0048。西安汉族:C6*A 0.4899、C6*B 0.4874、C6*B_2 0.0126和C6*R 0.0101。广东梅州客家人:C6*A 0.4569、C6*B 0.5152和C6*B_2 0.0279。C6*R为罕见等位基因之频率。     

Rod phosphodiesterase-6 PDE6A and PDE6B subunits are enzymatically equivalent

Phosphodiesterase-6 (PDE6) is the key effector enzyme of the phototransduction cascade in rods and cones. The catalytic core of rod PDE6 is a unique heterodimer of PDE6A and PDE6B catalytic subunits. The functional significance of rod PDE6 heterodimerization and conserved differences between PDE6AB and cone PDE6C and the individual properties of PDE6A and PDE6B are unknown. To address these outstanding questions, we expressed chimeric homodimeric enzymes, enhanced GFP (EGFP)-PDE6C-A and EGFP-PDE6C-B, containing the PDE6A and PDE6B catalytic domains, respectively, in transgenic Xenopus laevis. Similar to EGFP-PDE6C, EGFP-PDE6C-A and EGFP-PDE6C-B were targeted to the rod outer segments and concentrated at the disc rims. PDE6C, PDE6C-A, and PDE6C-B were isolated following selective immunoprecipitation of the EGFP fusion proteins. All three enzymes, PDE6C, PDE6C-A, and PDE6C-B, hydrolyzed cGMP with similar K(m) (20-23 μM) and k(cat) (4200-5100 s(-1)) values. Likewise, the K(i) values for PDE6C, PDE6C-A, and PDE6C-B inhibition by the cone- and rod-specific PDE6 γ-subunits (Pγ) were comparable. Recombinant cone transducin-α (Gα(t2)) and native rod Gα(t1) fully and potently activated PDE6C, PDE6C-A, and PDE6C-B. In contrast, the half-maximal activation of bovine rod PDE6 required markedly higher concentrations of Gα(t2) or Gα(t1). Our results suggest that PDE6A and PDE6B are enzymatically equivalent. Furthermore, PDE6A and PDE6B are similar to PDE6C with respect to catalytic properties and the interaction with Pγ but differ in the interaction with transducin. This study significantly limits the range of mechanisms by which conserved differences between PDE6A, PDE6B, and PDE6C may contribute to remarkable differences in rod and cone physiology.     

DNA sequence specificity of a naphthylquinoline triple helix-binding ligand.

We have examined the effect of a naphthylquinoline triplex-binding ligand on the formation of intermolecular triplexes on DNA fragments containing the target sites A6G6xC6T6 and G6A6xT6C6. The ligand enhances the binding of T6C2, but not T2C6, to A6G6xC6T6 suggesting that it has a greater effect on TxAT than C+xGC triplets. The complex with T6C2 is only stable below pH 6.0, confirming the requirement for protonation of the third strand cytosines. Antiparallel triplexes with GT-containing oligonucleotides are also stabilised by the ligand. The complex between G5T5 and A6G6xC6T6 is stabilised by lower ligand concentrations than that between T5G5 and G6A6xC6T6. The ligand does not promote the interaction with GT-containing oligonucleotides which have been designed to bind in a parallel orientation. Although the formation of antiparallel triplexes is pH independent, we find that the ligand has a greater stabilising effect at lower pH, suggesting that the active species is protonated. The ligand does not promote the binding of antiparallel GA-containing oligonucleotides at pH 7.5 but induces the interaction between A5G5 and G6A6xT6C6 at pH 5.5. Ethidium bromide does not promote the formation of any of these triplexes and destabilises the interaction of acridine-linked pyrimidine-containing third strands with these target sites.     

Biosynthesis of brassinosteroids in cultured cells of Catharanthus roseus

Precursor administration experiments with 2H-labeled 6-oxocampestanol, 6-deoxocastasterone and 6alpha-hydroxycastasterone in cultured cells of Catharanthus roseus were performed and the metabolites were analyzed by GC-MS. [2H6]Cathasterone was identified as a metabolite of [2H6]6-oxocampestanol, whereas [2H6]6alpha-hydroxycastasterone and [2H6]castasterone were identified as metabolites of [2H6]6-deoxocastasterone, and [2H6]castasterone was identified as a metabolite of [2H6]6alpha-hydroxycastasterone, indicating that 6-deoxocastasterone is converted to castasterone via 6alpha-hydroxycastasterone. In addition, 6-deoxocathasterone, a putative biosynthetic intermediate in the late C6-oxidation pathway, was identified as an endogenous brassinosteroid. These studies provide further evidence supporting our proposed biosynthetic pathways for brassinolide.     

高等植物葡萄糖-6- 磷酸脱氢酶与6- 磷酸葡萄糖酸脱氢酶基因的不同进化起源

葡萄糖-6-磷酸脱氢酶与6-磷酸葡萄糖酸脱氢酶是植物戊糖磷酸途径中的两个关键酶。在克隆了水稻质体葡萄糖-6-磷酸脱氢酶基因OsG6PDH2和质体6-磷酸葡萄糖脱氢酶基因Os6PGDH2基础上,分析比较了水稻胞质和质体葡萄糖-6-磷酸脱氢酶基因和6-磷酸葡萄糖酸脱氢酶基因的基因结构、表达特性和进化地位。结合双子叶模式植物拟南芥两种酶基因的分析结果,认为高等植物葡萄糖-6-磷酸脱氢酶基因和6-磷酸葡萄糖酸脱氢酶基因在进化方式上截然不同,葡萄糖-6-磷酸脱氢酶的胞质基因与动物和真菌等真核生物具有共同的祖先;6-磷酸葡萄糖酸脱氢酶的胞质酶和质体酶基因都起源于原核生物的内共生。讨论了植物葡萄糖-6-磷酸脱氢酶与6-磷酸葡萄糖酸脱氢酶基因可能的进化模式,为高等植物及质体的进化起源提供了新的资料。     

Reversal of some viral IL-6 electrostatic properties compared to IL-6 contributes to a loss of alpha receptor component recruitment

Human interleukin-6 (hIL-6) is a pleiotropic mediator of activation and proliferation across a large number of different cell types. Human herpesvirus-8 (HHV-8) has been associated with classical and AIDS-related Kaposi's sarcoma (KS). HHV-8 encodes viral IL-6 (vIL-6), a functional homolog of human interleukin-6, that promotes the growth of KS and of some lymphoma cells. Signaling induced by human IL-6 requires recruitment of the glycoprotein gp130, which acts as the signal transducing chain, and of IL-6Ralpha, which is necessary for cognate recognition and high affinity receptor complex formation. In contrast, the formation of a functional complex between vIL-6 and gp130 does not require the presence of IL-6Ralpha. The physico-chemical properties of vIL-6 have been analyzed and compared to those of hIL-6 and of the receptor chains, gp130 and IL-6Ralpha. Interaction sites on vIL-6 involve more hydrophobic residues than those of hIL-6. The electrostatic fields induced by vIL-6 and IL-6Ralpha are repulsive and prevent interaction between vIL-6 and IL-6Ralpha, whereas the electrostatic field induced by hIL-6 steers the complex formation with IL-6Ralpha. Subsequently, electrostatic binding free energy in the vIL-6/IL-6Ralpha complex is destabilizing, whereas it is stabilizing in the complex comprising hIL-6. These properties result from charge reversals between viral and human IL-6, an unusual phenomenon of amino acid substitutions within a homologous protein family. This suggests a selection pressure for vIL-6 to by-pass the IL-6Ralpha control of host defense against virus infection. This selection pressure has yielded the reversal of electrostatic properties of vIL-6 when compared to hIL-6.     

6′-substituted and 6′,6″-disubstituted derivatives of raffinose

The reaction of 6′-chloro-6′-deoxyraffinose deca-acetate with a variety of nucleophilic anions (Br^-,I^-,N^-₃) gave the corresponding 6′-substituted raffinoses. The 6′-azide was further converted into 6′-amino-6′-deoxyraffinose, isolated as its N-acetyl derivative, and silver fluoride-induced elimination of hydrogen iodide from the 6′-iodide gave the 6′-deoxy-5′-ene. Treatment of 6′-chloro-6′-deoxyraffinose and 6′,6″-dichloro-6′,6″-dideoxyraffinose with base afforded, respectively, 3′,6′-anhydro-and 3′,6′;3″,6″-dianhydro-raffinose in high yields. In addition, the dichloride was converted into 6′,6″-diazido-6′,6″-dideoxyraffinose.     

Artificial rearing with docosahexaenoic acid and n-6 docosapentaenoic acid alters rat tissue fatty acid composition

Docosahexaenoic acid (DHA; 22:6n-3) and n-6 docosapentaenoic acid (DPAn-6; 22:5n-6) are components of enriched animal feed and oil derived from Schizochytrium species microalgae. A one generation, artificial rearing model from day 2 after birth onward (AR) and a dam-reared control group (DAM) were used to examine DPAn-6 feeding on the fatty acid composition of various rat tissues at 15 weeks of age. Four AR diets were based on an n-3 fatty acid-deficient, 18:2n-6-based artificial milk with 22:6n-3 and/or 22:5n-6 added: AR-LA, AR-DHA, AR-DPAn-6, and AR-DHA+DPAn-6. The 22:6n-3 levels for the DAM, AR-DHA, and AR-DHA+DPAn-6 groups tended to be similar and higher than in the AR-LA and AR-DPAn-6 groups. The levels of 22:5n-6 tended to be higher only in the absence of dietary 22:6n-3. Adipose levels of 22:5n-6 was the only exception, as 22:5n-6 was significantly higher in AR-DHA+DPAn-6 than was observed in either the DAM or the AR-DHA group. There were no differences in 20:4n-6 levels within the tissues examined. In conclusion, 22:5n-6 replaces 22:6n-3 in the absence of 22:6n-3 only and does not appear to compete with 22:6n-3 in the presence of dietary 22:6n-3, suggesting that oils containing 22:5n-6 and 22:6n-3 may be a good dietary source of 22:6n-3.     

IL-6 Trans-Signaling via the Soluble IL-6 Receptor: Importance for the Pro-Inflammatory Activities of IL-6

Interleukin-6 (IL-6) is a cytokine with many activities. It has functions in the regulation of the immune system and the nervous system. Furthermore, IL-6 is involved in liver regeneration and in the metabolic control of the body. On target cells, IL-6 binds to an 80 kDa IL-6 receptor (IL-6R). The complex of IL-6 and IL-6R associates with a second protein, gp130, which thereupon dimerizes and initiates intracellular signaling. Whereas gp130 is expressed on all cells, IL-6R is only present on few cells in the body including hepatocytes and some leukocytes. Cells, which do not express IL-6R cannot respond to the cytokine, since gp130 alone has no measurable affinity for IL-6. Interestingly, a soluble form of IL-6R (sIL-6R) comprising the extracellular portion of the receptor can bind IL-6 with a similar affinity as the membrane bound IL-6R. The complex of IL-6 and sIL-6R can bind to gp130 on cells, which do not express the IL-6R, and which are unresponsive to IL-6. This process has been called trans-signaling. Here I will review published evidence that IL-6 trans-signaling is pro-inflammatory whereas classic IL-6 signaling via the membrane bound IL-6R is needed for regenerative or anti-inflammatory activities of the cytokine. Furthermore, the detailed knowledge of IL-6 biology has important consequences for therapeutic strategies aimed at the blockade of the cytokine IL-6.     

Identification of a second transforming function in bovine papillomavirus type 1 E6 and the role of E6 interactions with paxillin, E6BP, and E6AP

Papillomavirus E6 oncoproteins transform mammalian cells through interaction with cellular proteins. Bovine papillomavirus type 1 E6 (BE6) interacts with three previously described cellular targets: the E6AP E3 ubiquitin ligase, the calcium-binding protein E6BP (also known as ERC-55), and paxillin, which is a focal adhesion adapter protein. BE6 interacts strongly with each of these proteins in vitro, binding to similar peptide sequences found in E6AP, E6BP, and paxillin. To determine which BE6 interactions are necessary for transformation by BE6, we used a novel selection strategy for temperature-sensitive BE6 mutants in yeast that could discriminate in their interaction between E6AP, E6BP, and paxillin. All BE6 mutants that retained transforming ability retained association with paxillin, while some mutants that were transformation positive failed to interact with E6AP or E6BP. This study demonstrates that oncogene mutants that are temperature sensitive for transformation can be selected in yeast and that the induction of anchorage-independent cell proliferation by BE6 does not require strong association of BE6 with either E6AP or E6BP. Of particular interest is the identification of a BE6 mutant that interacts strongly with the acidic charged leucine motifs of E6AP, E6BP, and paxillin but is devoid of transformation activity, thereby genetically identifying a second essential transformation function in BE6 that is independent of interaction with acidic charged leucine motifs.     

Anti-peptide antibodies for examining the conformation, molecular assembly and localization of an intracellular protein, ribosomal protein S6, in vivo

Ribosomal protein S6 (rpS6) is known to relate to cell proliferation. Our recent proteome analysis of human metaphase chromosomes revealed the enrichment of rpS6 during mitosis. Here, structure, localization and molecular assembly in vitro and in vivo of a human rpS6, were examined using antibodies (Abs) prepared by immunizing rabbits with synthetic peptides. Five peptides, Ser6-Asp20 (S6-1), Ile52-Gly66 (S6-2), Asp103-Gly117 (S6-3), Asn146-Lys160 (S6-4) and Arg178-Ile192 (S6-5) were chosen as epitopes of human rpS6. These peptides except for S6-3 induced strong Ab production, and with an enzyme-linked immunosorbent assay, anti-S6-2, anti-S6-4 and anti-S6-5, showed high reactivity to recombinant rpS6 (r-rpS6), while anti-S6-1 did not, suggesting that S6-2, S6-4 and S6-5 were exposed on the r-rpS6 surface, while S6-1 was less exposed or possessed a different conformation. The immunostaining of HeLa cells as well as isolated chromosomes suggested that rpS6 occurs in endoplasmic reticulum (ER) but less possible on chromosomes since no Abs showed localization of rpS6 to chromosomes. In addition, the immunostaining suggested that only S6-4 is exposed on the protein surface, while S6-2 and S6-5 are buried by the interaction with other macromolecules in HeLa cells. Present our result shows new possibility of antibodies as tools for structure-oriented cell biology.     

The E6 oncoproteins from human betapapillomaviruses differentially activate telomerase through an E6AP-dependent mechanism and prolong the lifespan of primary keratinocytes

Human papillomaviruses (HPVs) belonging to the Betapapillomavirus genus have recently been implicated in squamous cell carcinomas of the skin, though the mechanisms by which they initiate carcinogenesis are unclear. We show that human foreskin keratinocytes (HFKs) expressing several betapapillomavirus E6 (beta-E6) proteins display life span extension, but not to the extent seen in HFKs expressing HPV type 16 E6 (16E6). Additionally, we demonstrate that beta-E6 proteins can differentially activate telomerase. HFKs expressing 38E6 exhibit significant telomerase activity but to a lesser degree than that observed with 16E6; however, other beta-E6 proteins, including 5E6, 8E6, 20E6, and 22E6, exhibit low or background levels of telomerase activity. Utilizing glutathione S-transferase pull-down and coimmunoprecipitation experiments, the beta-E6 proteins were shown to interact with the cellular proteins E6-associated protein (E6AP) and NFX1-91, two proteins known to be important for telomerase activation by 16E6. Interestingly, the relative strength of the interaction between E6 and E6AP or NFX1-91 was proportionate to the activation of telomerase by each beta-E6 protein. To address the requirement for E6AP in telomerase activation by beta-E6 proteins, we utilized a shRNA to knock down endogenous levels of E6AP. Lysates with decreased levels of E6AP showed a reduced ability to activate telomerase, suggesting that E6AP is a necessary component. These data suggest that complex formation between E6, E6AP, and NFX1-91 is a critical step in mediating telomerase activation, which may be one contributing factor to cellular life span extension during human betapapillomavirus infection.     

Absence of cross-reactivity between murine Ly-6C and Ly-6G.

BACKGROUND: The Ly-6 family has many members, including Ly-6C and Ly-6G. A previous study suggested that the anti-Ly-6G antibody, RB6-8C5, may react with Ly-6Chi murine bone marrow (BM) cells. This finding has been interpreted as cross-reactivity of RB6-8C5 with the Ly-6C antigen, and has been generalized to many hematopoietic cell types, using the terminology Ly-6G/C. The present study was undertaken to determine whether anti-Ly-6G antibodies truly cross-react with the Ly-6C antigen on multiple hematopoietic cell types. METHODS: Splenocytes, thymocytes, and BM cells obtained from Ly-6.1 and Ly-6.2 strains of mice were stained with a variety of antibodies to Ly-6C and Ly-6G. Flow cytometric analysis was performed on these populations. RESULTS: Evaluation of anti-Ly-6C and anti-Ly-6G staining showed only Ly-6C expression and no Ly-6G expression on subsets of splenic T and B cells and thymocytes from Ly-6.1 and Ly-6.2 mice. Bone marrow cells were identified that express both Ly-6G and Ly-6C; no Ly-6G+Ly-6C- populations were seen. CONCLUSIONS: Multiple Ly-6C+ hematopoietic cell populations were identified that do not stain with anti-Ly-6G antibodies. This calls into question the use of the Ly-6G/C nomenclature and suggests that epitopes recognized by anti-Ly-6G antibodies should simply be designated Ly-6G.     

Characterization of Six Bacteriophages of Serratia liquefaciens CP6 Isolated from the Sugar Beet Phytosphere

Six phages (ΦCP6-1 to ΦCP6-6) that are commonly found in the phytosphere of sugar beet (Beta vulgaris var. Amethyst) were investigated, and their relative impacts on their host (Serratia liquefaciens CP6) were compared. There were fundamental differences between the two most abundant predators of CP6 (ΦCP6-1 and ΦCP6-4). Like ΦCP6-2 and ΦCP6-5, ΦCP6-1 belonged to the family Siphoviridae, while ΦCP6-4 exhibited the morphology of the family Podoviridae. The other phages were members of the family Myoviridae. DNA-DNA cross-hybridization revealed that ΦCP6-1 and ΦCP6-4 had little common DNA, although all of the other phages exhibited some genetic similarity. Like ΦCP6-2, ΦCP6-3, and ΦCP6-5, ΦCP6-1 was capable of forming a lysogenic association with its host, while ΦCP6-4 and ΦCP6-6 appeared to be entirely virulent. Single-step growth curve experiments revealed that ΦCP6-4 had a much shorter latent period and a smaller burst size than ΦCP6-1. Also, ΦCP6-1 could transduce a number of host chromosomal markers with transfer frequencies of 2.9 × 10⁻⁹ to 3.9 × 10⁻⁷, whereas ΦCP6-4 could not transduce S. liquefaciens CP6 genes. When viewed in the context of the strikingly different temporal niches of these phages, our data provide an insight into how bacteriophage interactions with their hosts might reflect the natural ecology of bacteriophages. Our data also illustrate how the potential for gene transfer changes over time in an environment that supports several different phages.     

Carcinogenicity and metabolic profiles of 6-substituted benzo[a]pyrene derivatives on mouse skin

The ability was tested of appropriate substituents of benzo[a]pyrene (BP) at C-6 to decrease or suppress the carcinogenic activity for these BP derivatives relative to the parent compound. 8-week-old female Swiss mice in 9 groups of 30 were treated on the back with 0.2 mumol of compound in acetone 4 times weekly for 20 weeks. The following compounds were administered: BP, 6-methylbenzo[a]pyrene (BP-6-CH3), 6-hydroxymethylbenzo[a]pyrene (BP-6-CH2OH), benzo[a]pyrene-6-carboxaldehyde (BP-6-CHO), benzo[a]pyrene-6-carboxylic acid, 6-methoxybenzo[a]pyrene, 6-acetoxybenzo[a]pyrene, 6-bromobenzo[a]pyrene, and 6-iodobenzo[a]pyrene. Two additional groups received BP or BP-6-CH3 twice weekly for 20 weeks at a total dose 25% of that above. In addition, the metabolism of selected 6-substituted BP derivatives was studied, using mouse skin homogenates in vitro and mouse skin in vivo. Only four compounds were carcinogenic; the order of potency was BP greater than BP-6-CH3 greater than BP-6-CH2OH and BP-6-CHO. The difference in carcinogenicity between BP-6-CH2OH and BP-6-CHO could not be assessed by this experiment. In a further tumorigenesis experiment the carcinogenicity of BP-6-CH2OH was compared to that of BP-6 CHO, BP-6-CH3 and 6-hydroxymethylbenzo[a]pyrere sulfate ester (BP-6-CH2OSO3Na) on mouse skin. 9-week-old female Swiss mice in groups of 28 were treated at three dose levels with 0.8, 0.2 and 0.05 mumol of compounds in dioxane--dimethyl sulfoxide (75 : 25) twice weekly for 40 weeks. After 40 experimental weeks BP-6-CH2OSO3Na proved to be a more potent carcinogen than BP-6-CH2OH, which, in turn was more active than BP-6-CHO. The greater carcinogenicity of BP-6-CH3 relative to BP-6-CH2OH and BP-6-CHO is confirmed, suggesting that BP-6-CH2OH is not a proximate carcinogenic metabolite for BP-6-CH3. Since BP-6-CHO is a weaker carcinogen than BP-6-CH2OH and is efficiently reduced metabolically to BP-6-CH2OH, the latter compound may be a common proximal carcinogenic metabolite. The stronger potency of BP-6-CH2OSO3Na, compared to its alcohol, suggests that an ester of BP-6-CH2OH might be the ultimate alkylating compound reacting with cellular nucleophiles.     

The E6 and E7 genes of human papillomavirus type 6 have weak immortalizing activity in human epithelial cells.

Previous studies have shown that the E7 gene of human papillomavirus (HPV) type 16 or 18 alone was sufficient for immortalization of human foreskin epithelial cells (HFE) and that the efficiency was increased in cooperation with the respective E6 gene, whereas the HPV6 E6 or E7 gene was not active in HFE. To detect weak immortalizing activities of the HPV6 genes, cells were infected with recombinant retroviruses containing HPV genes, alone and in homologous and heterologous combinations. The HPV6 genes, alone or together (HPV6 E6 plus HPV6 E7), were not able to immortalize cells. However the HPV6 E6 gene, in concert with HPV16 E7, increased the frequency of immortalization threefold over that obtained with HPV16 E7 alone. Interestingly, 6 of 20 clones containing the HPV16 E6 gene and the HPV6 E7 gene were immortalized, whereas neither gene alone was sufficient. Thus, the HPV6 E6 and E7 genes have weak immortalizing activities which can be detected in cooperation with the more active transforming genes of HPV16. Acute expression of the HPV6 and HPV16 E6 and E7 genes revealed that only HPV16 E7 was able to stimulate the proliferation of cells in organotypic culture, resulting in increased expression of the proliferative cell nuclear antigen and the formation of a disorganized epithelial layer. Additionally, combinations of genes that immortalized HFE cells (HPV16 E6 plus HPV16 E7, HPV16 E6 plus HPV6 E7, and HPV6 E6 plus HPV16 E7) also stimulated proliferation.     

Human papillomavirus type 16 E6 induces self-ubiquitination of the E6AP ubiquitin-protein ligase

The E6 protein of the high-risk human papillomaviruses (HPVs) and the cellular ubiquitin-protein ligase E6AP form a complex which causes the ubiquitination and degradation of p53. We show here that HPV16 E6 promotes the ubiquitination and degradation of E6AP itself. The half-life of E6AP is shorter in HPV-positive cervical cancer cells than in HPV-negative cervical cancer cells, and E6AP is stabilized in HPV-positive cancer cells when expression of the viral oncoproteins is repressed. Expression of HPV16 E6 in cells results in a threefold decrease in the half-life of transfected E6AP. E6-mediated degradation of E6AP requires (i) the binding of E6 to E6AP, (ii) the catalytic activity of E6AP, and (iii) activity of the 26S proteasome, suggesting that E6-E6AP interaction results in E6AP self-ubiquitination and degradation. In addition, both in vitro and in vivo experiments indicate that E6AP self-ubiquitination results primarily from an intramolecular transfer of ubiquitin from the active-site cysteine to one or more lysine residues; however, intermolecular transfer can also occur in the context of an E6-mediated E6AP multimer. Finally, we demonstrate that an E6 mutant that is able to immortalize human mammary epithelial cells but is unable to degrade p53 retains its ability to bind and degrade E6AP, raising the possibility that E6-mediated degradation of E6AP contributes to its ability to transform mammalian cells.