Beta Human Papillomavirus 8E6 Attenuates LATS Phosphorylation after Failed Cytokinesis

Abstract

Beta genus human papillomaviruses (β-HPVs) cause cutaneous squamous cell carcinomas (cSCCs) in a subset of immunocompromised patients. However, β-HPVs are not necessary for tumor maintenance in the general population. Instead, they may destabilize the genome in the early stages of cancer development. Supporting this idea, β-HPV’s 8E6 protein attenuates p53 accumulation after failed cytokinesis. This paper offers mechanistic insight into how β-HPV E6 causes this change in cell signaling. An in silico screen and characterization of HCT 116 cells lacking p300 suggested that the histone acetyltransferase is a negative regulator of Hippo pathway (HP) gene expression. HP activation restricts growth in response to stimuli, including failed cytokinesis. Loss of p300 resulted in increased HP gene expression, including proproliferative genes associated with HP inactivation. β-HPV 8E6 expression recapitulates some of these phenotypes. We used a chemical inhibitor of cytokinesis (dihydrocytochalasin B [H2CB]) to induce failed cytokinesis. This system allowed us to show that β-HPV 8E6 reduced activation of large tumor suppressor kinase (LATS), an HP kinase. LATS is required for p53 accumulation following failed cytokinesis. These phenotypes were dependent on β-HPV 8E6 destabilizing p300 and did not completely attenuate the HP. It did not alter H2CB-induced nuclear exclusion of the transcription factor YAP. β-HPV 8E6 also did not decrease HP activation in cells grown to a high density. Although our group and others have previously described inhibition of DNA repair, to the best of our knowledge, this marks the first time that a β-HPV E6 protein has been shown to hinder HP signaling. IMPORTANCE β-HPVs contribute to cSCC development in immunocompromised populations. However, it is unclear if these common cutaneous viruses are tumorigenic in the general population. Thus, a more thorough investigation of β-HPV biology is warranted. If β-HPV infections do promote cSCCs, they are hypothesized to destabilize the cellular genome. In vitro data support this idea by demonstrating the ability of the β-HPV E6 protein to disrupt DNA repair signaling events following UV exposure. We show that β-HPV E6 more broadly impairs cellular signaling, indicating that the viral protein dysregulates the HP. The HP protects genome fidelity by regulating cell growth and apoptosis in response to a myriad of deleterious stimuli, including failed cytokinesis. After failed cytokinesis, β-HPV 8E6 attenuates phosphorylation of the HP kinase (LATS). This decreases some, but not all, HP signaling events. Notably, β-HPV 8E6 does not limit senescence associated with failed cytokinesis.

MicroRNA-18a targeting of the STK4/MST1 tumour suppressor is necessary for transformation in HPV positive cervical cancer

“…induce YAP-dependent gene transcription, and this may be through attenuating the activity of the Hippo kinase LATS [22]. Clearly, manipulation of Hippo signalling appears vital for HPV pathogenesis; however, the molecular mechanisms remain unclear.…”

Beta-Genus Human Papillomavirus 8 E6 Destabilizes the Host Genome by Promoting p300 Degradation

“…However, the role of p300 destabilization in escape from UV-induced cell cycle arrest was not tested in these studies. p300 destabilization allows HPV8 E6 to promote proliferation in the face of other genome destabilizing events and reduces differentiation both in vivo and in vitro [ 81 , 82 , 83 , 84 , 85 ]. One mechanism by which reduced p300 availability promotes proliferation is the dysregulation of the Hippo pathway.…”

“…One mechanism by which reduced p300 availability promotes proliferation is the dysregulation of the Hippo pathway. By destabilizing p300, HPV8 E6 increases the expression and protein levels of pro-proliferative Hippo pathway factors: CTGF, AXL, and SERPINE1 [ 82 ]. Altered Hippo pathway signaling has genome destabilizing consequences, as it allows cells to continue proliferating after failed cytokinesis, leading to viable cells with polyploid genomes [ 84 ].…”

“…This causes LATS2 to bind p53 and inhibit MDM-mediated degradation [ 101 , 102 ]. HPV8 E6 reduces LATS2 activation and prevents p53 buildup induced by cytokinesis failure [ 82 ]. However, HPV8 E6 does not affect the activation of the Hippo pathway in response to high cell density.…”

“…Genetic knockouts have the potential to eliminate these concerns and have been used to test the role of p300 in multiple HPV8 E6-mediated phenotypes [ 69 , 82 ]. Most commonly, colorectal cancer cell lines (HCT116) with and without the p300 gene knocked out are compared [ 119 ].…”