Production of Human Papillomavirus Type 16 E7 Protein in Lactococcus lactis

The E7 protein of human papillomavirus type 16 was produced in Lactococcus lactis. Secretion allowed higher production yields than cytoplasmic production. In stationary phase, amounts of cytoplasmic E7 were reduced, while amounts of secreted E7 increased, suggesting a phase-dependent intracellular proteolysis. Fusion of E7 to the staphylococcal nuclease, a stable protein, resulted in a highly stable cytoplasmic protein. This work provides new candidates for development of viral screening systems and for oral vaccine against cervical cancer.     

mRNA Instability Elements in the Human Papillomavirus Type 16 L2 Coding Region

Human papillomavirus capsid proteins L1 and L2 are detected only in terminally differentiated cells, indicating that expression of the L1 and L2 genes is blocked in dividing cells. The results presented here establish that the human papillomavirus type 16 L2 coding region contains cis-acting inhibitory sequences. When placed downstream of a reporter gene, the human papillomavirus type 16 L2 sequence reduced both mRNA and protein levels in an orientation-dependent manner. Deletion analysis revealed that the L2 sequence contains two cis-acting inhibitory RNA regions. We identified an inhibitory region in the 5′-most 845 nucleotides of L2 that acted by reducing cytoplasmic mRNA stability and a second, weaker inhibitory region in the 3′ end of L2. In contrast, human papillomavirus type 1 L1 and L2 genes did not encode strong inhibitory sequences. This result is consistent with observations of high virus production in human papillomavirus type 1-infected tissue, whereas only low levels of human papillomavirus type 16 virions are detectable in infected epithelium. The presence of inhibitory sequences in the L1 and L2 mRNAs may aid the virus in avoiding the host immunosurveillance and in establishing persistent infections.     

E5 Protein of Human Papillomavirus Type 16 Protects Human Foreskin Keratinocytes from UV B-Irradiation-Induced Apoptosis

The human papillomavirus type 16 (HPV16) E5 protein associates with the epidermal growth factor receptor (EGFR) and enhances the activation of the EGFR after stimulation by EGF in human keratinocytes. Phosphatidylinositol 3-kinase (PI3K) and ERK1/2 mitogen-activated protein kinase (ERK1/2 MAPK), two signal molecules downstream of the EGFR, have been recognized as participants in two survival signal pathways in response to stress. The fact that E5 can enhance EGFR activation suggests that E5 might act as a survival factor. To test this hypothesis, the apoptotic response of UV B-irradiated primary keratinocytes infected with either control retrovirus, LXSN, or HPV16 2E5-expressing recombinant retrovirus was quantitated. Under the same conditions, LXSN-infected cells showed extensive apoptosis, while E5-expressing cells demonstrated a significant reduction in UV B-irradiation-induced apoptosis. The E5-mediated protection against apoptosis was blocked by wortmannin and PD98059, specific inhibitors of the PI3K and ERK1/2 MAPK pathways, respectively, suggesting that the PI3K and ERK1/2 MAPK pathways are involved in this process. Western blot analysis showed that Akt (also named protein kinase B), which is a downstream effector of PI3K, and ERK1/2 MAPK were activated by EGF. When cells were stimulated by EGF and irradiated by UV B, the levels of phospho-Akt and phospho-ERK1/2 activated by EGF in E5-expressing cells were about twofold greater than those in LXSN-infected cells. Two other UV-activated stress pathways, p38 and JNK, were activated to the same level during UV B irradiation in both LXSN-infected cells and E5-expressing cells, indicating that E5 protein did not affect these two pathways. After UV B irradiation, p53 was activated in both LXSN-infected cells and E5-expressing cells, and cell cycle analysis showed that nearly all cells in both cell populations were growth arrested. These data suggest that unlike HPV16 E6, which blocks apoptosis by inactivation of p53, HPV16 E5 protects cells from apoptosis by enhancing the PI3K-Akt and ERK1/2 MAPK signal pathways.     

Membrane Orientation of the Human Papillomavirus Type 16 E5 Oncoprotein

The E5 protein of human papillomavirus type 16 is a small, hydrophobic protein that localizes predominantly to membranes of the endoplasmic reticulum (ER). To define the orientation of E5 in these membranes, we employed a differential, detergent permeabilization technique that makes use of the ability of low concentrations of digitonin to selectively permeabilize the plasma membrane and saponin to permeabilize all cellular membranes. We then generated a biologically active E5 protein that was epitope tagged at both its N and C termini and determined the accessibility of these termini to antibodies in the presence and absence of detergents. In both COS cells and human ectocervical cells, the C terminus of E5 was exposed to the cytoplasm, whereas the N terminus was restricted to the lumen of the ER. Finally, the deletion of the E5 third transmembrane domain (and terminal hydrophilic amino acids) resulted in a protein with its C terminus in the ER lumen. Taken together, these topology findings are compatible with a model of E5 being a 3-pass transmembrane protein and with studies demonstrating its C terminus interacting with cytoplasmic proteins.Human papillomaviruses (HPVs) are small, nonenveloped, double-stranded DNA viruses (25) that are the causative agents of benign and malignant tumors in humans (43). Most cancers of the cervix, vagina, and anus are caused by HPVs, as are a fraction of oropharyngeal cancers (29, 44). HPV type 16 (HPV-16) is the type most frequently found in anogenital cancers (15, 29), including cervical cancer, the most common cancer of women worldwide (44).Some of the biological activities of the HPV-16 E5 protein (16E5) include the augmentation of epidermal growth factor (EGF) signaling pathways (8), stimulation of anchorage-independent growth (38), alkalinization of endosomal pH (11), and alteration of membrane lipid composition (39). 16E5 also exhibits weak transforming activity in vitro (12), induces epithelial tumors in transgenic mice (13), and plays an important role in koilocytosis (20). There are multiple documented intracellular binding targets for 16E5 such as the 16-kDa subunit of the vacuolar H⁺-ATPase (7, 36), the heavy chain of HLA type I (1), EGF receptor family member ErbB4 (6), calnexin (16), the zinc transporter ZnT-1 (21), the EVER1 and EVER2 transmembrane channel-like proteins that modulate zinc homeostasis (21, 31), the nuclear import receptor family member karyopherin β3 (KNβ3) (19), and BAP31, which was previously reported to contribute to B-cell receptor activation (35).16E5 is a small, hydrophobic protein that localizes to intracellular membranes. When overexpressed in COS cells, it is present in the endoplasmic reticulum (ER) and, to a lesser extent, in the Golgi apparatus (7). At a lower level of expression in human foreskin keratinocytes and human ectocervical cells (HECs), 16E5 is present predominantly in the ER (10, 39). 16E5 contains three hydrophobic regions (14, 16, 22, 30, 41), and it was reported previously that the first hydrophobic region determines various biological properties of the protein (16, 22). It was also shown previously that the 16E5 C terminus plays a role in binding to karyopherin β3 (19) and in the formation of koilocytes (20). While theoretical predictions have been made for the topology of E5 in membranes (16), no experimental data exist. However, a recent study suggested that some highly expressed 16E5 localizes to the plasma membrane, with its C terminus exposed externally (18).The aim of the present study was to establish the orientation of 16E5 in the ER membrane. By using immunofluorescence microscopy coupled with differential membrane permeabilization (24, 34), we demonstrate the membrane orientation of an N- and C-terminally tagged, biologically active 16E5 protein. Our results indicate that the N terminus is intralumenal and that the C terminus is cytoplasmic, consistent with a model of E5 being a three-pass transmembrane protein and with current data on the interaction of its C terminus with cytoplasmic proteins.     

人乳头瘤病毒E2蛋白及其相关疫苗

人乳头瘤病毒（human papilloma virus,HPV）感染在全球范围内颇为常见,其与肛门生殖器疣、生殖器肿瘤的发生关系密切。研究发现,乳头瘤的形成与HPVE2蛋白密不可分,该蛋白质涉及到病毒生命周期的各个阶段,与病毒的有丝分裂、其他早期蛋白的转录及细胞凋亡有关。近年来,各国学者利用E2蛋白的特性研制出E2相关疫苗,分别使用不同的重组病毒来传输E2,或是使用纯化的E2蛋白或E2融合蛋白,运输至体内的HPV转化细胞和／或HPV感染细胞中,以期达到防治HPV感染相关疾病的目的。     

Cyclophilins Facilitate Dissociation of the Human Papillomavirus Type 16 Capsid Protein L1 from the L2/DNA Complex following Virus Entry

Human papillomaviruses (HPV) are composed of the major and minor capsid proteins, L1 and L2, that encapsidate a chromatinized, circular double-stranded DNA genome. At the outset of infection, the interaction of HPV type 16 (HPV16) (pseudo)virions with heparan sulfate proteoglycans triggers a conformational change in L2 that is facilitated by the host cell chaperone cyclophilin B (CyPB). This conformational change results in exposure of the L2 N terminus, which is required for infectious internalization. Following internalization, L2 facilitates egress of the viral genome from acidified endosomes, and the L2/DNA complex accumulates at PML nuclear bodies. We recently described a mutant virus that bypasses the requirement for cell surface CyPB but remains sensitive to cyclosporine for infection, indicating an additional role for CyP following endocytic uptake of virions. We now report that the L1 protein dissociates from the L2/DNA complex following infectious internalization. Inhibition and small interfering RNA (siRNA)-mediated knockdown of CyPs blocked dissociation of L1 from the L2/DNA complex. In vitro, purified CyPs facilitated the dissociation of L1 pentamers from recombinant HPV11 L1/L2 complexes in a pH-dependent manner. Furthermore, CyPs released L1 capsomeres from partially disassembled HPV16 pseudovirions at slightly acidic pH. Taken together, these data suggest that CyPs mediate the dissociation of HPV L1 and L2 capsid proteins following acidification of endocytic vesicles.