MEK/ERK signaling is a critical regulator of high-risk human papillomavirus oncogene expression revealing therapeutic targets for HPV-induced tumors.

Intracellular pathogens have evolved to utilize normal cellular processes to complete their replicative cycles. Pathogens that interface with proliferative cell signaling pathways risk infections that can lead to cancers, but the factors that influence malignant outcomes are incompletely understood. Human papillomaviruses (HPVs) predominantly cause benign hyperplasia in stratifying epithelial tissues. However, a subset of carcinogenic or "high-risk" HPV (hr-HPV) genotypes are etiologically linked to nearly 5% of all human cancers. Progression of hr-HPV-induced lesions to malignancies is characterized by increased expression of the E6 and E7 oncogenes and the oncogenic functions of these viral proteins have been widely studied. Yet, the mechanisms that regulate hr-HPV oncogene transcription and suppress their expression in benign lesions remain poorly understood. Here, we demonstrate that EGFR/MEK/ERK signaling, influenced by epithelial contact inhibition and tissue differentiation cues, regulates hr-HPV oncogene expression. Using monolayer cells, epithelial organotypic tissue models, and neoplastic tissue biopsy materials, we show that cell-extrinsic activation of ERK overrides cellular control to promote HPV oncogene expression and the neoplastic phenotype. Our data suggest that HPVs are adapted to use the EGFR/MEK/ERK signaling pathway to regulate their productive replicative cycles. Mechanistic studies show that EGFR/MEK/ERK signaling influences AP-1 transcription factor activity and AP-1 factor knockdown reduces oncogene transcription. Furthermore, pharmacological inhibitors of EGFR, MEK, and ERK signaling quash HPV oncogene expression and the neoplastic phenotype, revealing a potential clinical strategy to suppress uncontrolled cell proliferation, reduce oncogene expression and treat HPV neoplasia.

The antiviral effects of a MEK1/2 inhibitor promote tumor regression in a preclinical model of human papillomavirus infection-induced tumorigenesis.

Human papillomaviruses (HPVs) are a significant public health concern due to their widespread transmission, morbidity, and oncogenic potential. Despite efficacious vaccines, millions of unvaccinated individuals and those with existing infections will develop HPV-related diseases for the next two decades and beyond. The continuing burden of HPV-related diseases is exacerbated by the lack of effective therapies or cures for infections, highlighting the need to identify and develop antivirals. The experimental murine papillomavirus type 1 (MmuPV1) model provides opportunities to study papillomavirus pathogenesis in cutaneous epithelium, the oral cavity, and the anogenital tract. However, to date the MmuPV1 infection model has not been used to demonstrate the effectiveness of potential antivirals. We previously reported that inhibitors of cellular MEK/ERK signaling suppress oncogenic HPV early gene expression in three-dimensional tissue cultures. Herein, we adapted the MmuPV1 infection model to determine whether MEK inhibitors have anti-papillomavirus properties in vivo. We demonstrate that oral delivery of a MEK1/2 inhibitor promotes papilloma regression in immunodeficient mice that otherwise would have developed persistent infections. Quantitative histological analyses reveal that inhibition of MEK/ERK signaling reduces E6/E7 mRNA, MmuPV1 DNA, and L1 protein expression within MmuPV1-induced lesions. These data suggest that MEK1/2 signaling is essential for both early and late MmuPV1 replication events supporting our previous findings with oncogenic HPVs. We also provide evidence that MEK inhibitors protect mice from developing secondary tumors. Thus, our data suggest that MEK inhibitors have potent antiviral and anti-tumor properties in a preclinical mouse model and merit further investigation as papillomavirus antiviral therapies.

Inhibition of Cellular MEK/ERK Signaling Suppresses Murine Papillomavirus Type 1 Replicative Activities and Promotes Tumor Regression.

Human papillomaviruses (HPVs) are a significant public health concern due to their widespread transmission, morbidity, and oncogenic potential. Despite efficacious vaccines, millions of unvaccinated individuals and those with existing infections will develop HPV-related diseases for the next two decades. The continuing burden of HPV-related diseases is exacerbated by the lack of effective therapies or cures for most infections, highlighting the need to identify and develop antivirals. The experimental murine papillomavirus type 1 (MmuPV1) model provides opportunities to study papillomavirus pathogenesis in cutaneous epithelium, the oral cavity, and the anogenital tract. However, to date the MmuPV1 infection model has not been used to demonstrate the effectiveness of potential antivirals. We previously reported that inhibitors of cellular MEK/ERK signaling suppress oncogenic HPV early gene expression in vitro . Herein, we adapted the MmuPV1 infection model to determine whether MEK inhibitors have anti-papillomavirus properties in vivo . We demonstrate that oral delivery of a MEK1/2 inhibitor promotes papilloma regression in immunodeficient mice that otherwise would have developed persistent infections. Quantitative histological analyses revealed that inhibition of MEK/ERK signaling reduces E6/E7 mRNAs, MmuPV1 DNA, and L1 protein expression within MmuPV1-induced lesions. These data suggest that MEK1/2 signaling is essential for both early and late MmuPV1 replication events supporting our previous findings with oncogenic HPVs. We also provide evidence that MEK inhibitors protect mice from developing secondary tumors. Thus, our data suggest that MEK inhibitors have potent anti-viral and anti-tumor properties in a preclinical mouse model and merit further investigation as papillomavirus antiviral therapies. Significance Statement: Persistent human papillomavirus (HPV) infections cause significant morbidity and oncogenic HPV infections can progress to anogenital and oropharyngeal cancers. Despite the availability of effective prophylactic HPV vaccines, millions of unvaccinated individuals, and those currently infected will develop HPV-related diseases over the next two decades and beyond. Thus, it remains critical to identify effective antivirals against papillomaviruses. Using a mouse papillomavirus model of HPV infection, this study reveals that cellular MEK1/2 signaling supports viral tumorigenesis. The MEK1/2 inhibitor, trametinib, demonstrates potent antiviral activities and promotes tumor regression. This work provides insight into the conserved regulation of papillomavirus gene expression by MEK1/2 signaling and reveals this cellular pathway as a promising therapeutic target for the treatment of papillomavirus diseases.

Complete Genome Sequence of Citrobacter freundii Myophage Miller.

Citrobacter freundii is a Gram-negative, opportunistic pathogen that can be fatal to newborns or immunocompromised patients. Bacteriophages against this bacterium can be useful for therapeutic purposes. Here, we describe the complete genome and the key features of the pseudo T-even C. freundii bacteriophage Miller.

Complete Genome Sequence of Citrobacter freundii Myophage Moogle.

Citrobacter freundii is an opportunistic pathogen that has been linked to nosocomial infections, such as brain abscesses and pneumonia. Further study on phages infecting C. freundii may provide therapeutics for these infections. Here, we announce the complete genome sequence of the FelixO1-like myophage Moogle and describe its features.

Complete Genome Sequence of Citrobacter freundii Myophage Moon.

Citrobacter freundii and other Gram-negative opportunistic pathogens necessitate concern from the public health sector. Bacteriophages that kill such pathogens may be useful in the control and containment of these infections. Here, we describe the genome of a newly isolated T4-like myophage of C. freundii, Moon, and present its features.

Complete Genome of Salmonella enterica Serovar Typhimurium T5-Like Siphophage Stitch.

Salmonellosis, caused by Salmonella, is a leading cause of food poisoning worldwide. With the continuing rise of bacterial antibiotic resistance, efforts are focused on seeking new approaches for treatment of bacterial infections, namely, bacteriophage therapy. Here, we report the complete genome of S. Typhimurium siphophage Stitch.

Complete Genome of Citrobacter freundii Siphophage Stevie.

Citrobacter freundii is an opportunistic pathogen responsible for many urinary tract infections acquired in hospitals and is thus a concern for public health. C. freundii phage Stevie might prove beneficial as a treatment against these infections. The complete genome of Stevie and its key features are described here.

Complete Genome of Salmonella enterica Serovar Enteritidis Myophage Marshall.

Salmonella enterica serovar Enteritidis is a food-borne pathogen that causes salmonellosis in the United States. Bacteriophages are emerging as viable biocontrol agents against this pathogen. Here, we present the complete annotated genome sequence of Salmonella Enteritidis T4-like myophage Marshall, which has potential as a phage therapy agent.