Toll-like Receptor 4 Mediates Innate Immunity to Kaposi Sarcoma Herpesvirus

The involvement of Toll-like receptor 4 (TLR4) in immunity against human herpesviruses has not been previously demonstrated. We show that infection of endothelial cells with Kaposi sarcoma herpesvirus (KSHV), a human oncogenic virus, leads to rapid suppression of TLR4 expression. This is a mechanism of immune escape as TLR4 mediates innate immunity against KSHV. In vitro, cells lacking TLR4 are more susceptible to KSHV infection, whereas activation of TLR4 protects cells from infection. In vivo, HIV-1-infected individuals carrying a mutant TLR4 allele appear more likely to have multicentric Castleman's disease, a lymphoproliferation associated with enhanced KSHV replication. ERK activation by KSHV structural proteins and the KSHV-encoded vGPCR plays a key role in the TLR4 downregulation, whereas the KSHV vIRF1 also contributes to this effect. Our findings reveal a role for TLR4 in innate immunity against herpesviruses and suggest the potential use of TLR4 agonists for the treatment of KSHV-related neoplasms

Opposing Regulation of PROX1 by Interleukin-3 Receptor and NOTCH Directs Differential Host Cell Fate Reprogramming by Kaposi Sarcoma Herpes Virus

Lymphatic endothelial cells (LECs) are differentiated from blood vascular endothelial cells (BECs) during embryogenesis and this physiological cell fate specification is controlled by PROX1, the master regulator for lymphatic development. When Kaposi sarcoma herpes virus (KSHV) infects host cells, it activates the otherwise silenced embryonic endothelial differentiation program and reprograms their cell fates. Interestingly, previous studies demonstrated that KSHV drives BECs to acquire a partial lymphatic phenotype by upregulating PROX1 (forward reprogramming), but stimulates LECs to regain some BEC-signature genes by downregulating PROX1 (reverse reprogramming). Despite the significance of this KSHV-induced bidirectional cell fate reprogramming in KS pathogenesis, its underlying molecular mechanism remains undefined. Here, we report that IL3 receptor alpha (IL3Rα) and NOTCH play integral roles in the host cell type-specific regulation of PROX1 by KSHV. In BECs, KSHV upregulates IL3Rα and phosphorylates STAT5, which binds and activates the PROX1 promoter. In LECs, however, PROX1 was rather downregulated by KSHV-induced NOTCH signal via HEY1, which binds and represses the PROX1 promoter. Moreover, PROX1 was found to be required to maintain HEY1 expression in LECs, establishing a reciprocal regulation between PROX1 and HEY1. Upon co-activation of IL3Rα and NOTCH, PROX1 was upregulated in BECs, but downregulated in LECs. Together, our study provides the molecular mechanism underlying the cell type-specific endothelial fate reprogramming by KSHV

Higher Nevus Count Exhibits a Distinct DNA Methylation Signature in Healthy Human Skin: Implications for Melanoma

High naevus count is the strongest risk factor for melanoma and although gene variants have been discovered for both traits, epigenetic variation is unexplored. We investigated 322 healthy human skin DNA methylomes associated with total body naevi count, incorporating genetic and transcriptomic variation. DNA methylation changes were identified at genes involved in melanocyte biology, such as RAF1 (p = 1.2 x 10(-6)) and CTC1 (region: p = 6.3 x 10(-4)), and other genes including ARRDC1 (p = 3.1 x 10(-7)). A subset exhibited coordinated methylation and transcription changes within the same biopsy. The total analysis was also enriched for melanoma-associated DNA methylation variation (p = 6.33 x 10(-6)). Additionally, we show that skin DNA methylation is associated in cis with known GWAS SNPs for naevus count, at PLA2G6 (p = 1.7 x 10(-49)) and NID1 (p = 6.4 x 10(-14)), as well as melanoma risk, including in or near MC1R, MX2 and TERT/CLPTM1L (p < 1 x 10(-10)). Our analysis using a uniquely large dataset comprising healthy skin DNA methylomes identified known and additional regulatory loci and pathways in naevi and melanoma biology. This integrative study improves our understanding of predisposition to naevi and their potential contribution to melanoma pathogenesis

KSHV Manipulates Notch Signaling by DLL4 and JAG1 to Alter Cell Cycle Genes in Lymphatic Endothelia

Increased expression of Notch signaling pathway components is observed in Kaposi sarcoma (KS), but the mechanism underlying the manipulation of the canonical Notch pathway by the causative agent of KS, Kaposi sarcoma herpesvirus (KSHV), has not been fully elucidated. Here, we describe the mechanism through which KSHV directly modulates the expression of the Notch ligands JAG1 and DLL4 in lymphatic endothelial cells. Expression of KSHV-encoded vFLIP induces JAG1 through an NF kappa B-dependent mechanism, while vGPCR upregulates DLL4 through a mechanism dependent on ERK. Both vFLIP and vGPCR instigate functional Notch signalling through NOTCH4. Gene expression profiling showed that JAG1- or DLL4-stimulated signaling results in the suppression of genes associated with the cell cycle in adjacent lymphatic endothelial cells, indicating a role for Notch signaling in inducing cellular quiescence in these cells. Upregulation of JAG1 and DLL4 by KSHV could therefore alter the expression of cell cycle components in neighbouring uninfected cells during latent and lytic phases of viral infection, influencing cellular quiescence and plasticity. In addition, differences in signaling potency between these ligands suggest a possible complementary role for JAG1 and DLL4 in the context of KS

C-RAF Mutations in human cancer

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The microRNA-30 family targets DLL4 to modulate endothelial cell behavior during angiogenesis.

Delta-like 4 (DLL4), a membrane-bound ligand belonging to the Notch signaling family, plays a fundamental role in vascular development and angiogenesis. We identified a conserved microRNA family, miR-30, which targets DLL4. Overexpression of miR-30b in endothelial cells led to increased vessel number and length in an in vitro model of sprouting angiogenesis. Microinjection of miR-30 mimics into zebrafish embryos resulted in suppression of dll4 and subsequent excessive sprouting of intersegmental vessels and reduction in dorsal aorta diameter. Use of a target protector against the miR-30 site within the dll4 3'UTR up-regulated dll4 and synergized with Vegfa signaling knockdown to inhibit angiogenesis. Furthermore, restoration of miR-30b or miR-30c expression during Kaposi sarcoma herpesvirus (KSHV) infection attenuated viral induction of DLL4. Together these results demonstrate that the highly conserved molecular targeting of DLL4 by the miR-30 family regulates angiogenesis