Roles of the PDZ‐binding motif of HPV 16 E6 protein in oncogenic transformation of human cervical keratinocytes

Abstract

The high‐risk human papillomavirus E6 proteins have been shown to interact with and lead to degradation of PDZ‐domain‐containing proteins through its carboxy‐terminal motif. This PDZ‐binding motif plays important roles in transformation of cultured cells and carcinogenesis of E6‐transgenic mice. However, its biological effects on the natural host cells have not been elucidated. We have examined its roles in an in vitro carcinogenesis model for cervical cancer, in which E6 and E7 together with activated HRAS (HRASG 12V) can induce tumorigenic transformation of normal human cervical keratinocytes. In this model, E6Δ151 mutant, which is defective in binding to PDZ domains, almost lost tumorigenic ability, whereas E6SAT mutant, which is defective in p53 degradation showed activity close to wild‐type E6. Interestingly, we found decreased expression of PAR3 in E6‐expressing cells independently of E6AP, which has not been previously recognized. Therefore, we knocked down several PDZ‐domain containing proteins including PAR3 in human cervical keratinocytes expressing E7, HRASG 12V and E6Δ151 to examine whether depletion of these proteins can restore the tumorigenic ability. Single knockdown of SCRIB, MAGI1 or PAR3 significantly but partially restored the tumorigenic ability. The combinatorial knockdown of SCRIB and MAGI1 cooperatively restored the tumorigenic ability, and additional depletion of PAR3 further enhanced the tumorigenic ability surpassing that induced by wild‐type E6. These data highlight the importance of the carboxy‐terminal motif of the E6 protein and downregulation of PAR3 in tumorigenic transformation of human cervical keratinocytes.

Upsetting the Balance: When Viruses Manipulate Cell Polarity Control

“…Interaction with hScrib and the TJ protein ZO2, however, was limited to the PBMs of virus types with a strong cancer association (HPV types 16,18,31,33,35,51), suggesting that the greater disruption of the Scrib complex caused by the combined loss of hScrib and hDlg1, particularly in the context of a long-term persistent infection, has a greater risk of disrupting cellular polarity in a manner that favors malignant transformation. Indeed, this has been recently confirmed in cellular transformation assays [52]. Human cervical keratinocytes exogenously expressing activated Ras, plus HPV-16 wild-type E6 and E7, are capable of anchorage-independent growth and are tumorigenic in nude mice.…”

“…Expression in this system of an E6 defective in PDZ-binding prevents this, but the tumorigenic phenotype can be slightly rescued by the individual ablation of DLG1 or DLG4 (also known as PSD-95) and partially rescued by ablation of either hScrib, MAGI-1 or PAR3. However, ablation of hScrib plus DLG1 and DLG4, or hScrib plus MAGI1 and PAR3 in this system actually enhances the tumorigenic phenotype above that of cells expressing the wild-type HPV-16 E6 [52], demonstrating the pivotal importance of hScrib targeting in HPVinduced malignancy.…”

Cancer exosomes induce tumor innervation

“…HPV16 induces OPSCC and is thus considered a high risk HPV; 53 low risk HPVs rarely cause cancer. One important difference between high and low risk HPVs is found in their E6 proteins; only high risk E6 contains a C-terminal PDZ binding motif (PDZBM) which contributes to oncogenic transformation 54 , 55 . In fact, E6’s PDZBM mediates interactions with a number of different proteins that contribute to oncogenic activity 56 – 61 .…”

Competing endogenous RNA network profiling reveals novel host dependency factors required for MERS-CoV propagation

“…For example, protein tyrosine phosphatase receptor kappa (PTPRK) is downregulated by Epstein-Barr virus in Hodgkin lymphoma (HL), leading to suppressed transforming growth factor-beta (TGF-β) signalling [41]. Membrane-associated guanylate kinase with inverted organization-1 (MAGI-1) is a PDZ protein that interacts with viral proteins containing the PDZ-ligand binding motif, such as influenza A virus NS1, human papillomavirus 16 E6, and human alphapapillomavirus E6 proteins [41][42][43]. Notably, the different putative circRNAs generated from the same host gene might demonstrate diversified expressions.…”