Production of L1 protein from different types of HPV in Pichia pastoris using an integrative vector

Human papillomavirus (HPV) infection is the most common sexually transmitted disease in the world and is related to the etiology of cervical cancer. The most common high-risk HPV types are 16 and 18; however, the second most prevalent type in the Midwestern region of Brazil is HPV-33. New vaccine strategies against HPV have shown that virus-like particles (VLP) of the major capsid protein (L1) induce efficient production of antibodies, which confer protection against the same viral type. The methylotrophic yeast Pichia pastoris is an efficient and inexpensive expression system for the production of high levels of heterologous proteins stably using a wild-type gene in combination with an integrative vector. It was recently demonstrated that P. pastoris can produce the HPV-16 L1 protein by using an episomal vector associated with the optimized L1 gene. However, the use of an episomal vector is not appropriate for protein production on an industrial scale. In the present study, the vectors were integrated into the Pichia genome and the results were positive for L1 gene transcription and protein production, both intracellularly and in the extracellular environment. Despite the great potential for expression by the P. pastoris system, our results suggest a low yield of L1 recombinant protein, which, however, does not make this system unworkable. The achievement of stable clones containing the expression cassettes integrated in the genome may permit optimizations that could enable the establishment of a platform for the production of VLP-based vaccines.

Production of immunogenic human papillomavirus-16 major capsid protein derived virus like particles.

Background & objective: Recombinant DNA technology allows expression of the human papillomavirus (HPV) major capsid protein (L1) in heterologous expression systems and the recombinant protein self assembles to virus-like particles (VLP). We took up this study to produce recombinant HPV-16 L1 in yeast, establish the process of recombinant L1 derived VLP preparation and develop an ELISA using VLP as the antigen for serological evaluation of anti HPV-16 L1 antibody status. Methods: Complete HPV-16 L1 was amplified from genomic DNA of an esophageal cancer biopsy, cloned and the protein was expressed in a galactose-inducible Saccharomyces cerevisiae expression system. Self assembled VLP was purified by a two-step density gradient centrifugation process and the VLP preparation used to test its suitability in developing an ELISA. Results: The recombinant protein was predominantly a ~55 KD species with distinct immunoreactivity and formed VLP as confirmed by electron microscopy. An ELISA using the VLP showed its efficacy in appropriate immunoreactivity to serum/plasma IgG. Interpretation & conclusions: Recombinant HPV-16 capsid protein derived VLP was produced and the VLP antigen based ELISA can be used to probe serological association of HPV with different clinical conditions. The VLP technology can be improved further and harnessed for future vaccine development efforts in the country.

Posible papel del factor de transcripción AP1 en la regulación tejido-específica del papilomavirus humano / Possible role of transcription factor AP1 in the tissue-specific regulation of human papillomavirus

Activator protein-1 (AP1) is a dimeric protein, consisting either of homodimers between c-Jun, JunB, and JunD of by heterodimers with members of the Fos-family by physically interacting via a "leucine zipper" region. AP1 is an important transcription factor initially identified as a DNA binding protein that bound to enhancer sequences of the human metallothionein IIA gene. The protein components of AP1 are encoded by a set of genes known as "immediate-early" genes that can be activated by a variety of growth factors and mitogens through several different signaling pathways. Until recently, AP1 was considered a transcription factor expressed in most tissues to regulate cellular and viral genes now, it is becoming evident that AP1 can be involved in tissue-specific regulation of target genes due to the differential combination of the components of this important transcription factor. AP1 plays a crucial role during human papillomavirus (HPV) early gene expression, in particular of the expression of E6 and E7 oncoproteins. The HPV are a group of DNA viruses consisting of more than 80 different genotypes. Some of these HPV, know as high risk HPV, are important etiologic agents of uterine-cervical cancer (CaCu). Of the different types of cancer, CaCu is one of the most frequent among women worldwide, constituting the second death cause due to neoplasia. During cellular transformation, HPV infect basal cells in stratified epithelium; their DNA integrate into the host genome usually through the E2 gene; as these cells differentiate and migrate into the upper layer of the epithelium, viral oncogene are expressed blocking their differentiation. Mutagenesis in AP1 sites belonging to the HPV promoter region (LCR) completely abolished the HPV promoter activity in different cell lines; these results and biochemistry assays on this AP1 transcription factor, that includes protein-protein interactions between AP1 and another factors as E7 from HPV, and YY-1; the post-translattional modification and, the retinoic acid interaction; suggest a role for this AP1 factor in tissue-specific transcription of the human papillomavirus.

Expression and localization of human papillomavirus type 16 E6 and E7 open reading frame proteins in human epidermal keratinocyte

Over 60 different types of human papillomavirus (HPV) have been identified, and they are classified into high and low risk groups based on the risk for malignant progression of HPV associated lesions. HPVs belonging to a high risk group have been shown to express two major transforming proteins, E6 and E7. With respect to the transforming activity of these proteins, many investigators have reported the location of these proteins in the cell, but their results are still controversial. In the present study, HPV type 16 E6 or E7 open reading frame (ORF) proteins were expressed and localized in human epidermal keratinocytes (RHEK-1) using the vaccinia virus as an expression vector. Immunofluorescence detection using monoclonal antibodies against E6 or E7 ORF proteins revealed that E6 or E7 proteins of HPV type 16 were located in the cytoplasm of RHEK-1 cells. These results suggest that E6 and E7 proteins bind to the tumor suppressor counterparts, thereby preventing transport of these proteins into the nucleus. These antioncogene products that fail to be rapidly transported out of the cytosol may be degraded by certain proteases such as the ubiquitin dependent system. In this way, the precise function of antioncogene products in the regulation of cell growth could be destroyed, and abnormal cell growth could occur.