Regulation of HPV E7 Stability by E6-Associated Protein (E6AP)

The membrane-associated ubiquitin ligase MARCHF8 stabilizes the human papillomavirus oncoprotein E7 by degrading CUL1 and UBE2L3 in head and neck cancer

The human papillomavirus (HPV) oncoprotein E7 is a relatively short-lived protein required for HPV-driven cancer development and maintenance. E7 is degraded through ubiquitination mediated by cullin 1 (CUL1) and the ubiquitin-conjugating enzyme E2 L3 (UBE2L3). However, E7 proteins are maintained at high levels in most HPV-positive cancer cells. A previous proteomics study has shown that UBE2L3 and CUL1 protein levels are increased by the knockdown of the E3 ubiquitin ligase membrane-associated ring-CH-type finger 8 (MARCHF8). We have recently demonstrated that HPV16 upregulates MARCHF8 expression in HPV-positive keratinocytes and head and neck cancer (HPV+ HNC) cells. Here, we report that MARCHF8 stabilizes the HPV16 E7 protein by degrading the components of the S-phase kinase-associated protein 1-CUL1-F-box ubiquitin ligase complex in HPV+ HNC cells. We found that MARCHF8 knockdown in HPV+ HNC cells drastically decreases the HPV16 E7 protein level while increasing the CUL1 and UBE2L3 protein levels. We further revealed that the MARCHF8 protein binds to and ubiquitinates CUL1 and UBE2L3 proteins and that MARCHF8 knockdown enhances the ubiquitination of the HPV16 E7 protein. Conversely, the overexpression of CUL1 and UBE2L3 in HPV+ HNC cells decreases HPV16 E7 protein levels and suppresses tumor growth in vivo. Our findings suggest that HPV-induced MARCHF8 prevents the degradation of the HPV16 E7 protein in HPV+ HNC cells by ubiquitinating and degrading CUL1 and UBE2L3 proteins.IMPORTANCESince human papillomavirus (HPV) oncoprotein E7 is essential for virus replication; HPV has to maintain high levels of E7 expression in HPV-infected cells. However, HPV E7 can be efficiently ubiquitinated by a ubiquitin ligase and degraded by proteasomes in the host cell. Mechanistically, the E3 ubiquitin ligase complex cullin 1 (CUL1) and ubiquitin-conjugating enzyme E2 L3 (UBE2L3) components play an essential role in E7 ubiquitination and degradation. Here, we show that the membrane ubiquitin ligase membrane-associated ring-CH-type finger 8 (MARCHF8) induced by HPV16 E6 stabilizes the E7 protein by degrading CUL1 and UBE2L3 and blocking E7 degradation through proteasomes. MARCHF8 knockout restores CUL1 and UBE2L3 expression, decreasing E7 protein levels and inhibiting the proliferation of HPV-positive cancer cells. Additionally, overexpression of CUL1 or UBE2L3 decreases E7 protein levels and suppresses in vivo tumor growth. Our results suggest that HPV16 maintains high E7 protein levels in the host cell by inducing MARCHF8, which may be critical for cell proliferation and tumorigenesis.

The membrane-associated ubiquitin ligase MARCHF8 stabilizes the human papillomavirus oncoprotein E7 by degrading CUL1 and UBE2L3 in head and neck cancer

The human papillomavirus (HPV) oncoprotein E7 is a relatively short-lived protein required for HPV-driven cancer development and maintenance. E7 is degraded through ubiquitination mediated by cullin 1 (CUL1) and the ubiquitin-conjugating enzyme E2 L3 (UBE2L3). However, E7 proteins are maintained at high levels in most HPV-positive cancer cells. A previous proteomics study has shown that UBE2L3 and CUL1 protein levels are increased by the knockdown of the E3 ubiquitin ligase membrane-associated ring-CH-type finger 8 (MARCHF8). We have recently demonstrated that HPV upregulates MARCHF8 expression in HPV-positive keratinocytes and head and neck cancer (HPV+ HNC) cells. Here, we report that MARCHF8 stabilizes the E7 protein by degrading the components of the SKP1-CUL1-F-box (SCF) ubiquitin ligase complex in HPV+ HNC cells. We found that MARCHF8 knockdown in HPV+ HNC cells drastically decreases the E7 protein level while increasing the CUL1 and UBE2L3 protein levels. We further revealed that the MARCHF8 protein binds to and ubiquitinates CUL1 and UBE2L3 proteins and that MARCHF8 knockdown enhances the ubiquitination of the E7 protein. Conversely, the overexpression of CUL1 and UBE2L3 in HPV+ HNC cells decreases E7 protein levels and suppresses tumor growth in vivo. Our findings suggest that HPV-induced MARCHF8 prevents the degradation of the E7 protein in HPV+ HNC cells by ubiquitinating and degrading CUL1 and UBE2L3 proteins.

p16INK4a and pRb expression in laryngeal squamous cell carcinoma with and without infection by EBV or different genotypes of HPV: a retrospective study

BACKGROUND

Laryngeal squamous cell carcinoma (LSCC) represents one of the principal tumors of the head and neck. Human papillomavirus (HPV) and Epstein-Barr virus (EBV) are considered risk factors for the development and the clinical prognosis of LSCC. High levels of p16^INK4a are suggested as a surrogate marker of HPV or EBV infection in some head and neck tumors but in LSCC is still controversial. Furthermore, pRb expression may be considered an additional biomarker but it has not been clearly defined. This work aimed to compare the expression of pRb and p16^INK4a as possible biomarkers in tumor tissues with and without infection by EBV or different genotypes of HPV from patients with LSCC.

METHODS

Tumor samples from 103 patients with LSCC were previously investigated for the presence and genotypes of HPV using the INNO-LiPA line probe assay and for the infection of EBV by qPCR. p16 ^INK4a and pRb expression was assessed by immunohistochemistry.

RESULTS

Of the 103 tumor samples, expression of p16^INK4a was positive in 55 (53.4%) and of this, 32 (56.1%) were positive for HPV whereas 11 (39.3%) were EBV positive but both without a significantly difference (p > 0.05). pRb expression was positive in 78 (75.7%) and a higher frequency of this expression was observed in HPV negative samples (87.0%) (p = 0.021) and in high-risk HPV negative samples (85.2%) (p = 0.010). No difference was observed when comparing pRb expression and EBV infection status (p > 0.05).

CONCLUSION

Our results support the suggestion that p16^INK4a is not a reliable surrogate marker for identifying HPV or EBV infection in LSCC. On the other hand, most of our samples had pRb expression, which was more frequent in tumors without HPV, suggesting that pRb could indicate HPV negativity. However, more studies with a larger number of cases are required, including controls without LSCC and evaluating other molecular markers to determine the real role of p16^INK4a and pRb in LSCC.

Elevated Expression of ADAM10 Induced by HPV E6 Influences the Prognosis of Cervical Cancer

Objective: To explore the abnormal expression of ADAM10, its cause, and its clinical value in the prognosis of cervical lesions. Methods: The abnormal expression of ADAM10 was explored using the Gene Expression Profiling Interactive Analysis database, and the abnormal expression in cervical lesions was verified using immunohistochemistry (IHC). The transfection effect of shRNA was evaluated using real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The expression of ADAM10 in cells was analyzed using western blotting. Results: ADAM10 was highly expressed in multiple cancers. As the disease progressed, the expression of ADAM10 gradually increased (p < 0.05). Patients with higher expression of ADAM10 had poorer survival outcomes than those with lower expression levels (p < 0.05). The expression levels of ADAM10 decreased after expression levels of E6 was inhibited. Conclusion: ADAM10 is highly expressed in cervical cancer; the higher the expression levels, the worse the survival outcome. HPV E6 is the critical driver of the elevated expression of ADAM10 in cervical cancer.

Expression of Progesterone Receptor A as an Independent Negative Prognosticator for Cervical Cancer

The role of progesterone receptor A (PRA) for the survival outcome of cervical cancer patients is ambiguous. In mouse models, it has been shown that PRA plays a rather protective role in cancer development. The aim of this study was to assess its expression by immunohistochemistry in 250 cervical cancer tissue samples and to correlate the results with clinicopathological parameters including patient survival. PRA expression was positively correlated with the International Federation of Gynecology and Obstetrics (FIGO) classification scores. PRA was significantly overexpressed in adenocarcinomas compared to squamous epithelial carcinoma subtypes. Correlation analyses revealed a trend association with the HPV virus protein E6, a negative correlation with p16 and a positive correlation with EP3. PRA expression was also associated with the expression of RIP140, a transcriptional coregulator that we previously identified as a negative prognostic factor for survival in cervical cancer patients. Univariate survival analyses revealed PRA as a negative prognosticator for survival in patients with cervical adenocarcinoma. Multivariate analyses showed that simultaneous expression of RIP140 and PRA was associated with the worst survival, whereas with negative RIP140, PRA expression alone was associated with the best survival. We can therefore assume that the effect of nuclear PRA on overall survival is dependent upon nuclear RIP140 expression.