Smurf2 alters BPV1 trafficking and decreases infection

Intermediate heparan sulfate binding during HPV-16 infection in HaCaTs

Human papillomavirus (HPV) is the most prevalent sexually transmitted disease in the United States and can cause cancer with persistent infection. The most common cancer caused by HPV is cervical carcinoma with an average of 12,000 cases reported every year in the United States. Worldwide, over 500,000 cases of cervical cancer are reported yearly with over 250,000 deaths attributed to the disease. Although much is known about the serious health risks associated with HPV infection, there is still much to be discovered about how HPV binds and enters target cells. Understanding is required on how HPV infections will lead to strategies and therapies for reducing the number of infections and HPV-related diseases, including cancers. The HPV viral particle is composed of 2 viral proteins, L1 and L2. Data suggest that binding of the viral capsid to cells is dependent on the L1 protein. We hypothesize that this initial binding to a heparan sulfate is composed of 2 independent events: the first results in a structural change that exposes a hidden portion of the L1 protein leading to a second binding event on the heparan sulfate. Our experiments tested if this "hidden" portion of L1 is necessary for infection and explored the nature of this binding. We generated a peptide with the sequence of the "hidden" portion of L1. Infection of HaCaT cells in the presence of this peptide is highly reduced. Our results suggest that the binding of the L1 C-terminal domain is dependent on amino acid sequence and is necessary for infection.

Significance of expression of Smad ubiquitination regulatory factors in liver fibrosis

AIM: To observe the expression of Smad ubiquitination regulatory factor (Smurf)1, Smurf2, Smad3 and Smad7 proteins in liver fibrosis and to evaluate their interactions.

METHODS: Immunohistochemistry was applied to detect the expression of Smurf1, Smurf2, Smad3 and Smad7 in 9 normal liver tissue samples and 38 chronic HBV infection tissue samples.

RESULTS: Smurf1, Smurf2, Smad3 and Smad7 showed widespread expression in the liver parenchymal cells and nonparenchymal cells. Compared with normal liver tissue, the positive rates of Smad3 and Smurf2 expression increased significantly (66.7% vs 100%, 66.7% vs 92.1%, P < 0.01 for both) and the positive rate of Smad7 expression decreased significantly in liver fibrosis (77.8% vs 39.5%, P < 0.01), although the positive rate of Smurf1 expression had no significant change (77.8% vs 63.2%, P > 0.05). There were significant positive correlations between Smad3 and Smurf2 expression and the degree of fibrosis (P < 0.01 for both). Smad7 expression was negatively correlated with the degree of fibrosis (P < 0.01). There was no significant correlation between Smurf1 expression and liver fibrosis (P > 0.05). Smurf2 expression was positively correlated with Smad3 expression (P < 0.01) and negatively with Smad7 expression (P < 0.01). There was no significant relationship between Smurf1 and Smurf2, Smad3, Smad7 expression (P > 0.05 for all). There was a negative correlation between expression of Smad3 and that of Smad7 (P < 0.01).

CONCLUSION: The increase of Smad3 signal and decrease of Smad7 signal may lead to the development of liver fibrosis, and Smurf2 may play a bidirectionally regulatory role in the progression of liver fibrosis.

Smurf2 negatively modulates RIG-I-dependent antiviral response by targeting VISA/MAVS for ubiquitination and degradation

VISA (also known as MAVS, Cardif, IPS-1) is the essential adaptor protein for virus-induced activation of IFN regulatory factors 3 and 7 and production of type I IFNs. Understanding the regulatory mechanisms for VISA will provide detailed insights into the positive or negative regulation of innate immune responses. In this study, we identified Smad ubiquitin regulatory factor (Smurf) 2, one of the Smad ubiquitin regulator factor proteins, as an important negative regulator of virus-triggered type I IFN signaling, which targets at the VISA level. Overexpression of Smurf2 inhibits virus-induced IFN-β and IFN-stimulated response element activation. The E3 ligase defective mutant Smurf2/C716A loses the ability to suppress virus-induced type I IFN signaling, suggesting that the negative regulation is dependent on the ubiquitin E3 ligase activity of Smurf2. Further studies demonstrated that Smurf2 interacted with VISA and targeted VISA for K48-linked ubiquitination, which promoted the degradation of VISA. Consistently, knockout or knockdown of Smurf2 expression therefore promoted antiviral signaling, which was correlated with the increase in protein stability of VISA. Our findings suggest that Smurf2 is an important nonredundant negative regulator of virus-triggered type I IFN signaling by targeting VISA for K48-linked ubiquitination and degradation.

Evidence for polygenic adaptation to pathogens in the human genome

Most approaches aiming at finding genes involved in adaptive events have focused on the detection of outlier loci, which resulted in the discovery of individually "significant" genes with strong effects. However, a collection of small effect mutations could have a large effect on a given biological pathway that includes many genes, and such a polygenic mode of adaptation has not been systematically investigated in humans. We propose here to evidence polygenic selection by detecting signals of adaptation at the pathway or gene set level instead of analyzing single independent genes. Using a gene-set enrichment test to identify genome-wide signals of adaptation among human populations, we find that most pathways globally enriched for signals of positive selection are either directly or indirectly involved in immune response. We also find evidence for long-distance genotypic linkage disequilibrium, suggesting functional epistatic interactions between members of the same pathway. Our results show that past interactions with pathogens have elicited widespread and coordinated genomic responses, and suggest that adaptation to pathogens can be considered as a primary example of polygenic selection.