The HPV8 E6 protein targets the Hippo and Wnt signaling pathways as part of its arsenal to restrain keratinocyte differentiation

IMPORTANCE

Human papillomaviruses (HPVs) infect basal epithelial cells and cause a dramatic expansion of basal-like, proliferative cells. This reflects the ability of papillomaviruses to delay keratinocyte differentiation, thereby maintaining aspects of the basal cell identity of persistently infected cells. This may enable papillomaviruses to establish and maintain long-term infections in squamous epithelial tissues. Previous work has revealed that the ability of β-HPV8 E6 protein to inhibit Notch and transforming growth factor β signaling importantly contributes to this activity. Here, we present evidence that HPV8 E6 also subverts Hippo and Wnt signaling and that these activities also aid in restraining keratinocyte differentiation.

Mechanistic Contributions of lncRNAs to Cellular Signaling Pathways Crucial to the Lifecycle of Human Papillomaviruses

Papillomaviruses are ubiquitous epitheliotropic viruses with double-stranded circular DNA genomes of approximately 8000 base pairs. The viral life cycle is somewhat unusual in that these viruses can establish persistent infections in the mitotically active basal epithelial cells that they initially infect. High-level viral genome replication ("genome amplification"), the expression of capsid proteins, and the formation of infectious progeny are restricted to terminally differentiated cells where genomes are synthesized at replication factories at sites of double-strand DNA breaks. To establish persistent infections, papillomaviruses need to retain the basal cell identity of the initially infected cells and restrain and delay their epithelial differentiation program. To enable high-level viral genome replication, papillomaviruses also need to hold the inherently growth-arrested terminally differentiated cells in a replication-competent state. To provide ample sites for viral genome synthesis, they target the DNA damage and repair machinery. Studies focusing on delineating cellular factors that are targeted by papillomaviruses may aid the development of antivirals. Whilst most of the current research efforts focus on protein targets, the majority of the human transcriptome consists of noncoding RNAs. This review focuses on one specific class of noncoding RNAs, long noncoding RNAs (lncRNAs), and summarizes work on lncRNAs that may regulate the cellular processes that are subverted by papillomavirus to enable persistent infections and progeny synthesis.

Noncanonical Wnt/Ror2 Signaling Regulates Basal Cell Fidelity and Branching Morphogenesis in the Mammary Gland

The mammary gland epithelium relies on a delicate balance between basal and luminal cell lineages to maintain tissue homeostasis and enable proper development. While the role of canonical Wnt signaling in mammary biology is well-established, the contribution of noncanonical Wnt signaling to lineage identity has remained unclear. Noncanonical Wnt pathways are primarily associated with morphogenesis, cytoskeletal regulation, and cell migration, but whether they are required for maintaining epithelial cell fate remains largely unexplored. Here, we demonstrate that the noncanonical Wnt receptor Ror2 is expressed in both basal and luminal lineages, yet selectively maintained in basal cells throughout development, suggesting a lineage-specific function. Using a p63CreERT2/+ lineage-specific mouse model, we show that Ror2 deletion in basal epithelial cells enhances secondary and tertiary branching while driving a basal-to-luminal fate transition, marked by downregulation of basal markers (K14, K5) and upregulation of luminal markers (K8, K18, ERα). Mechanistically, Ror2 loss disrupts RhoA-ROCK1-YAP1 signaling, leading to cytoskeletal reorganization, chromatin remodeling, and increased accessibility at luminal regulatory loci. Notably, ROCK1 inhibition phenocopies Ror2 loss, reinforcing the critical role of the RhoA-ROCK1 axis in basal cell maintenance. These findings provide direct genetic and mechanistic evidence that noncanonical Wnt signaling is essential for maintaining basal lineage fidelity, offering new insights into the mechanisms regulating epithelial plasticity. Given the fundamental importance of lineage stability in epithelial homeostasis, our results suggest that disruptions in Wnt/Ror2 signaling may contribute to aberrant fate transitions relevant to breast cancer progression.