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 ß-HPV8 E6 protein to inhibit Notch and transforming growth factor ß 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.

The tumor cell-secreted matricellular protein WISP1 drives pro-metastatic collagen linearization.

Collagen linearization is a hallmark of aggressive tumors and a key pathogenic event that promotes cancer cell invasion and metastasis. Cell-generated mechanical tension has been proposed to contribute to collagen linearization in tumors, but it is unknown whether other mechanisms play prominent roles in this process. Here, we show that the secretome of cancer cells is by itself able to induce collagen linearization independently of cell-generated mechanical forces. Among the tumor cell-secreted factors, we find a key role in this process for the matricellular protein WISP1 (CCN4). Specifically, WISP1 directly binds to type I collagen to promote its linearization in vitro (in the absence of cells) and in vivo in tumors. Consequently, WISP1-induced type I collagen linearization facilitates tumor cell invasion and promotes spontaneous breast cancer metastasis, without significantly affecting gene expression. Furthermore, higher WISP1 expression in tumors from cancer patients correlates with faster progression to metastatic disease and poor prognosis. Altogether, these findings reveal a conceptually novel mechanism whereby pro-metastatic collagen linearization critically depends on a cancer cell-secreted factor.