Nelfinavir Inhibition of Kaposi's sarcoma-associated herpesvirus protein expression and capsid assembly

Background

Antiviral therapies that target herpesviruses are clinically important. Nelfinavir is a protease inhibitor that targets the human immunodeficiency virus (HIV) infections aspartyl protease. Previous studies demonstrated that this drug could also inhibit Kaposi's sarcoma-associated herpesvirus (KSHV) production. Our laboratory demonstrated nelfinavir can effectively inhibit herpes simplex virus type 1 (HSV-1) replication. For HSV-1 we were able to determine that virus capsids were assembled and exited the nucleus but did not mature in the cytoplasm indicating the drug inhibited secondary envelopment of virions.

Methods

For KSHV, we recently derived a tractable cell culture system that allowed us to analyze the virus replication cycle in detail. We used this system to further define the stage at which nelfinavir inhibits KSHV replication.

Results

We discovered that nelfinavir inhibits KSHV extracellular virus production. This was seen when the drug was incubated with the cells for 3 days and when we pulsed the cells with the drug for 1-5 minutes. When KSHV infected cells exposed to the drug were examined using ultrastructural methods there was an absence of mature capsids in the nucleus indicating a defect in capsid assembly. Because nelfinavir influences the integrated stress response (ISR), we examined the expression of viral proteins in the presence of the drug. We observed that the expression of many were significantly changed in the presence of drug. The accumulation of the capsid triplex protein ORF26 was markedly reduced. This is an essential protein required for herpesvirus capsid assembly.

Conclusions

Our studies confirm that nelfinavir inhibits KSHV virion production by disrupting virus assembly and maturation. Of interest is that inhibition requires only a short exposure to drug. The source of infectious virus in saliva has not been defined in detail but may well be lymphocytes or other cells in the oral mucosa. Thus, it might be that a "swish and spit" exposure rather than systemic administration would prevent virion production.

Kaposi's sarcoma-associated herpesvirus ubiquitin ligases downregulate cell surface expression of l-selectin

Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic etiological factor for Kaposi's sarcoma and primary effusion lymphoma in immunocompromised patients. KSHV utilizes two immune evasion E3 ubiquitin ligases, namely K3 and K5, to downregulate the expression of antigen-presenting molecules and ligands of natural killer (NK) cells in the host cells through an ubiquitin-dependent endocytic mechanism. This allows the infected cells to evade surveillance and elimination by cytotoxic lymphocytes and NK cells. The number of host cell molecular substrates reported for these ubiquitin ligases is limited. The identification of novel substrates for these ligases will aid in elucidating the mechanism underlying immune evasion of KSHV. This study demonstrated that K5 downregulated the cell surface expression of l-selectin, a C-type lectin-like adhesion receptor expressed in the lymphocytes. Tryptophan residue located at the centre of the E2-binding site in the K5 RINGv domain was essential to downregulate l-selectin expression. Additionally, the lysine residues located at the cytoplasmic tail of l-selectin were required for the K5-mediated downregulation of l-selectin. K5 promoted the degradation of l-selectin through polyubiquitination. These results suggest that K5 downregulates l-selectin expression on the cell surface by promoting polyubiquitination and ubiquitin-dependent endocytosis, which indicated that l-selectin is a novel substrate for K5. Additionally, K3 downregulated l-selectin expression. The findings of this study will aid in the elucidation of a novel immune evasion mechanism in KSHV.

Recurrence and Occurrence of Kaposi's Sarcoma in Patients Living With Human Immunodeficiency Virus (HIV) and on Antiretroviral Therapy, Despite Suppressed HIV Viremia

In 21 cutaneous and/or visceral Kaposi's sarcoma cases, occurring in patients living with human immunodeficiency virus (HIV) who were on antiretroviral therapy with suppressed HIV viremia and high CD4 T cell counts, the efficacy of conventional chemotherapies was limited due to cumulative toxicities, comedications, and a lack of immune improvement.

Seroprevalence of antibodies against Kaposi's sarcoma-associated herpesvirus among HIV-negative people in China

BACKGROUND

Little information on the prevalence of Kaposi's sarcoma associated herpesvirus (KSHV) among HIV-negative individuals is available from Asia.

METHODS

In the present study, we report findings from a new survey of KSHV in 983 HIV-negative male migrants from Shanghai and their combination with previous similar surveys of 600 female migrants, 600 female sex-workers (FSW), 1336 sexually transmitted infection (STI) clinic male patients, 439 intravenous drug-users (IVDU), and 226 men having sex with men (MSM) from China. KSHV-specific antibodies against latent and lytic antigens were assessed using Sf9 and BC3 monoclonal immunofluorescence assay. Age-adjusted prevalence ratios (PR) and 95% confidence interval (95% CI) for KSHV-positivity were estimated using Poisson regression.

RESULTS

In total, 4184 HIV-negative participants were included. KSHV prevalence ranged from 9.8% (95% CI: 7.9%-11.7%) in male migrants to 32.3% (95% CI: 24.1%-34.1%) in MSM. IVDU show intermediate level (17.5%, 95%CI: 14.1%-21.4%). KSHV was associated with syphilis (PR = 2.03, 95% CI: 1.38-2.98) in MSM but not in other groups. An association with human herpes virus 2 was also found among MSM (PR = 1. 83, 95%: 1.22-2.75) but not in migrant workers or FSW.

CONCLUSIONS

KSHV prevalence in HIV-negative heterosexuals, FSW, and STI male patients from China is approximately 10%, but 2- and 3-fold higher in IVDU and MSM, respectively. Associations of KSHV with STIs among MSM only suggest that sexual transmission of the virus is important in MSM but not in heterosexuals.

Herpesviruses and intermediate filaments: close encounters with the third type

Intermediate filaments (IF) are essential to maintain cellular and nuclear integrity and shape, to manage organelle distribution and motility, to control the trafficking and pH of intracellular vesicles, to prevent stress-induced cell death, and to support the correct distribution of specific proteins. Because of this, IF are likely to be targeted by a variety of pathogens, and may act in favor or against infection progress. As many IF functions remain to be identified, however, little is currently known about these interactions. Herpesviruses can infect a wide variety of cell types, and are thus bound to encounter the different types of IF expressed in each tissue. The analysis of these interrelationships can yield precious insights into how IF proteins work, and into how viruses have evolved to exploit these functions. These interactions, either known or potential, will be the focus of this review.