Samuel K Campos
Associate Professor, BIO5 Institute
Associate Professor, Cancer Biology - GIDP
Associate Professor, Immunobiology
Associate Professor, Molecular and Cellular Biology
Primary Department
Department Affiliations
(520) 626-4842
Work Summary
We aim to understand the mechanisms of HPV infection, the cellular responses to HPV infection, and how the interplay between host and virus influences the outcome
Research Interest
Samuel Campos, PhD, studies early events of Human Papillomavirus (HPV) infection. HPVs are small, non-enveloped DNA viruses that cause a variety of lesions ranging from benign waters to cervical cancers. Although over 100 types of HPVs have been identified, HPV16 is the most prevalent, and is alone responsible for more than 50% of cervical cancers in women worldwide. Dr. Campos and his lab study the mechanisms of HPV virus transmission at a cellular level, in hopes to discover new approaches for the prevention and treatment of HPV.HPV16 virions consist of an ~8kb circular dsDNA genome packaged into a ~60 nm protein capsid. The genome is condensed with cellular histones and exists in a chromatin-like state. The capsid is comprised of 72 pentamers of the major capsid protein L1 and up to 72 molecules of the minor capsid protein L2, localized along the inner capsid surface, within the central cavities beneath the L1 pentamers. Mature HPV16 virions exist in an oxidized state, with adjacent L1 pentamers crosslinked together by disulfide bonds to stabilize the capsid. In order to establish an infection, HPV16 virions must bind and penetrate host cells, ultimately delivering their genomes to the host cell nucleus to initiate early gene expression, cell cycle progression, and genome replication. Non-enveloped viruses are faced with the challenge of getting their genetic material across a cellular membrane and often overcome this by disrupting the endosomal or lysosomal membranes and translocating to the cellular cytoplasm during the course of intracellular virion trafficking. Keywords: virology, microbiology, virus-host interaction, HPV

Publications

Marsh, M. P., Campos, S. K., Baker, M. L., Chen, C. Y., Chiu, W., & Barry, M. A. (2006). Cryoelectron microscopy of protein IX-modified adenoviruses suggests a new position for the C terminus of protein IX. Journal of virology, 80(23), 11881-6.

Recombinant human adenovirus is a useful gene delivery vector for clinical gene therapy. Minor capsid protein IX of adenovirus has been of recent interest since multiple studies have shown that modifications can be made to its C terminus to alter viral tropism or add molecular tags and/or reporter proteins. We examined the structure of an engineered adenovirus displaying the enhanced green fluorescent protein (EGFP) fused to the C terminus of protein IX. Cryoelectron microscopy and reconstruction localized the C-terminal EGFP fusion between the H2 hexon and the H4 hexon, positioned between adjacent facets, directly above the density previously assigned as protein IIIa. The original assignment of IIIa was based largely on indirect evidence, and the data presented herein support the reassignment of the IIIa density as protein IX.

Campos, S. K. (2017). Subcellular Trafficking of the Papillomavirus Genome during Initial Infection: The Remarkable Abilities of Minor Capsid Protein L2. Viruses, 9(12).

Since 2012, our understanding of human papillomavirus (HPV) subcellular trafficking has undergone a drastic paradigm shift. Work from multiple laboratories has revealed that HPV has evolved a unique means to deliver its viral genome (vDNA) to the cell nucleus, relying on myriad host cell proteins and processes. The major breakthrough finding from these recent endeavors has been the realization of L2-dependent utilization of cellular sorting factors for the retrograde transport of vDNA away from degradative endo/lysosomal compartments to the Golgi, prior to mitosis-dependent nuclear accumulation of L2/vDNA. An overview of current models of HPV entry, subcellular trafficking, and the role of L2 during initial infection is provided below, highlighting unresolved questions and gaps in knowledge.

Campos, S. K., & Ozbun, M. A. (2009). Two highly conserved cysteine residues in HPV16 L2 form an intramolecular disulfide bond and are critical for infectivity in human keratinocytes. PloS one, 4(2), e4463.

Minor capsid protein L2 performs an indispensable but uncharacterized role in human papillomavirus infections. A neutralizing B cell epitope has recently been mapped to the N-terminus of HPV16 L2, residues 17-36, and exposure of this region of L2 has been implicated in translocation of incoming virions from the endo/lysosomal compartment to the cellular cytoplasm. Here we examine the redox state of Cys22 and Cys28 two highly conserved cysteines located within this epitope. We also investigate the infectivity of virions containing L2 single and double cysteine point mutants.

Bronnimann, M. P., Calton, C. M., Chiquette, S. F., Li, S., Lu, M., Chapman, J. A., Bratton, K. N., Schlegel, A. M., & Campos, S. K. (2016). Furin Cleavage of L2 During Papillomavirus Infection: Minimal Dependence on Cyclophilins. Journal of virology.

Despite an abundance of evidence supporting an important role for the cleavage of minor capsid protein L2 by cellular furin, direct cleavage of capsid-associated L2 during Human Papillomavirus Type 16 (HPV16) infection remains poorly characterized. The conserved cleavage site, close to the L2 N-terminus, confounds observation and quantification of the small cleavage product by SDS-PAGE. To overcome this difficulty, we increased the size shift by fusing a compact protein domain, the Propionibacterium shermanii transcarboxylase domain (PSTCD), to the N-terminus of L2. The infectious PSTCD-L2 virus displayed an appreciable L2 size shift during infection of HaCaT keratinocytes. Cleavage under standard cell culture conditions rarely exceeded 35% of total L2. Cleavage levels were enhanced by the addition of exogenous furin and the absolute levels of infection correlated to the level of L2 cleavage. Cleavage occurs on both the HaCaT cell surface and ECM. Contrary to current models, experiments on the involvement of cyclophilins revealed little if any role for these cellular enzymes in the modulation of furin cleavage. HPV16 L2 contains two consensus cleavage sites, Arg5 (2RHKR5) and Arg12 (9RTKR12). Mutant PSTCD-L2 viruses demonstrated that although furin can cleave either site, cleavage must occur at Arg12 as cleavage at Arg5 alone is insufficient for successful infection. Mutation of the conserved cysteine residues reveal that the Cys22-Cys28 disulfide bridge is not required for cleavage. The PSTCD-L2 virus or similar N-terminal fusions will be valuable tools to study additional cellular and viral determinants of furin cleavage.

Campos, S. K., Parrott, M. B., & Barry, M. A. (2004). Avidin-based targeting and purification of a protein IX-modified, metabolically biotinylated adenoviral vector. Molecular therapy : the journal of the American Society of Gene Therapy, 9(6), 942-54.

While genetic modification of adenoviral vectors can produce vectors with modified tropism, incorporation of targeting peptides/proteins into the structural context of the virion can also result in destruction of ligand targeting or virion integrity. To combat this problem, we have developed a versatile targeting system using metabolically biotinylated adenoviral vectors bearing biotinylated fiber proteins. These vectors have been demonstrated to be useful as a platform for avidin-based ligand screening and vector targeting by conjugating biotinylated ligands to the virus using high-affinity tetrameric avidin (K(d) = 10(-15) M). The biotinylated vector could also be purified by biotin-reversible binding on monomeric avidin (K(d) = 10(-7) M). In this report, a second metabolically biotinylated adenovirus vector, Ad-IX-BAP, has been engineered by fusing a biotin acceptor peptide (BAP) to the C-terminus of the adenovirus pIX protein. This biotinylated vector displays twice as many biotins and was markedly superior for single-step affinity purification on monomeric avidin resin. However, unlike the fiber-biotinylated vector, Ad-IX-BAP failed to retarget to cells with biotinylated antibodies including anti-CD71 against the transferrin receptor. In contrast, Ad-IX-BAP was retargeted if transferrin, the cognate ligand for CD71, was used as a ligand rather than the anti-CD71. This work demonstrates the utility of metabolic biotinylation as a molecular screening tool to assess the utility of different viral capsid proteins for ligand display and the biology and compatibility of different ligands and receptors for vector targeting applications. These results also demonstrate the utility of the pIX-biotinylated vector as a platform for gentle single-step affinity purification of adenoviral vectors.