Biology subjects

Ramaswami, R.

Publications and source records attributed to Ramaswami, R..

4 recordsLinked to original sources

bioRxiv2024

Mapping herpesvirus-driven impacts on the cellular milieu and transcriptional profile of Kaposi sarcoma in patient-derived mouse models

Kaposi sarcoma (KS) is defined by aberrant angiogenesis driven by Kaposi sarcoma herpesvirus (KSHV)-infected spindle cells with endothelial characteristics. KS research is hindered by rapid loss of KSHV infection upon explant culture of tumor cells. Here, we establish patient-derived KS xenografts (PDXs) upon orthotopic implantation of cutaneous KS biopsies in immunodeficient mice. KS tumors were maintained in 27/28 PDX until experimental endpoint, up to 272 days in the first passage of recipient mice. KSHV latency associated nuclear antigen (LANA)+ endothelial cell density increased by a mean 4.3-fold in 14/15 PDX analyzed by IHC at passage 1 compared to respective input biopsies, regardless of implantation variables and clinical features of patients. The Ki-67 proliferation marker colocalized with LANA more frequently in PDXs. Spatial transcriptome analysis revealed increased expression of viral transcripts from latent and lytic gene classes in the PDX. The expanded KSHV+ regions of the PDX maintained signature gene expression of KS tumors, with enrichment in pathways associated with angiogenesis and endothelium development. Cells with characteristics of tumor-associated fibroblasts derived from PDX were propagated for 15 passages. These fibroblast-like cells were permissive for de novo KSHV infection, and one lineage produced CXCL12, a cancer-promoting chemokine. Spatial analysis revealed that fibroblasts are a likely source of CXCL12 signaling to CXCR4 that was upregulated in KS regions. The reproducible expansion of KSHV-infected endothelial cells in PDX from multiple donors and recapitulation of a KS tumor gene signature supports the application of patient-derived KS mouse models for studies of pathogenesis and novel therapies. One Sentence SummaryTumor virus-driven expansion of endothelial cells with a transcriptional signature of Kaposi sarcoma in a large cohort of patient-derived xenografts provides a platform to discover cell communications within the tumor microenvironment.

microbiology↗

bioRxiv2024

The Elevated Expression of ORF75, a Lytic KSHV Gene, in Kaposi Sarcoma Lesions is Driven by a GC-rich DNA cis Element in its Promoter Region

The spindle cells of Kaposi sarcoma (KS) lesions primarily express Kaposi sarcoma herpesvirus (KSHV) latent genes with minimal expression of lytic genes. However, recent transcriptome analyses of KS lesions have shown high expression of KSHV open reading frame (ORF) 75, which is considered a late lytic gene based on analyses in primary effusion lymphoma (PEL) lines. ORF75 encodes a pseudo-amidotransferase that is part of the viral tegument, acts as a suppressor of innate immunity, and is essential for viral lytic replication. We assessed a representative KS lesion by RNAscope and found that ORF75 RNA was expressed in the majority of latency-associated nuclear antigen (LANA)-expressing cells. Luciferase fusion reporter constructs of the ORF75 promoter were analyzed for factors potentially driving its expression in KS. The ORF75 promoter construct showed high basal transcriptional activity in vitro in endothelial cells, mediated by a proximal consensus specificity protein 1 (Sp1) (GGGGCGGGGC) element along with two distal CCAAT boxes. Sp proteins formed complexes with the proximal consensus Sp1 element to activate ORF75 promoter transcription. We also found evidence that a repressive factor or factors in B cells, but not endothelial or epithelial cells, interacted with more distal elements in the ORF75 promoter region to repress constitutive ORF75 expression in B cells. Alternate forms of Sp1 were found to accumulate during latency and showed substantial enrichment during viral lytic replication in PEL cells and infected endothelial cells, but their functional significance is unclear. We also found that ORF75 can in turn upregulate its own expression and that of other KSHV genes. Thus, while ORF75 acts primarily as a lytic gene in PEL cell lines, Sp proteins induce substantial constitutive ORF75 transcription in infected endothelial cells and this can account for its high expression in KS lesions. Author SummaryIn our study, we explored KSHV ORF75, a tegument protein that is increasingly being appreciated as playing a vital role in KSHV replication and inactivating the innate immune response. ORF75 is characterized as a late lytic protein but has been recently found to be consistently expressed in Kaposis sarcoma (KS) lesions, which generally express only latent KSHV genes. Our findings reveal that ORF75 is constitutively expressed in endothelial and epithelial cells, and to a lesser extent B-cells. We found that constitutive expression of ORF75 is largely mediated by specificity (Sp) proteins binding to a proximal Sp1 site in the ORF75 promoter region. Moreover, we found that the lower expression of ORF75 in KSHV-infected B cells is due to suppressive factors acting at a more distal region of the ORF75 promoter. We further found that ORF75 can enhance expression of its own RNA as well as that of several other KSHV proteins, including replication and transcription activator (RTA) and latency associated nuclear antigen (LANA). This constitutive expression of ORF75, a late lytic gene, can explain how it can play such an important role in the earlier steps in KSHV lytic activation and underscores the importance of this gene.

microbiology↗

bioRxiv2022

Transcriptional analysis identifies overlapping and tissue-distinct profiles between Kaposi sarcoma tumors of the skin and gastrointestinal tract

Kaposi sarcoma (KS), caused by Kaposi sarcoma herpesvirus (KSHV), is a multicentric tumor characterized by abnormal vasculature and proliferation of KSHV-infected spindle cells. KS commonly involves the skin but in severe cases KS can also involve the gastrointestinal tract (GI). Here, we sought to compare the cellular and KSHV gene expression signatures of skin and GI KS lesions. Skin and GI KS were compared to normal matched samples using bulk RNA sequencing.Twenty-two paired samples of KS and normal tissue were obtained (skin (10 pairs) and GI (12 pairs)) from 19 patients with KS of whom 17 had concurrent HIV infection. Seven paired samples were from patients who had received prior KS therapy. Three patients provided both skin and GI samples at the same timepoint. These analyses identified 370 differentially expressed genes unique to cutaneous KS and 58 DEGs unique to GI KS compared to normal skin or GI tissues. Twenty-six differentially expressed genes overlapped between skin and GI KS, which included FLT4, which encodes for a VEGF-C and VEGF-D receptor, and STC1. KSHV infection of primary lymphatic endothelial cells (LECs) resulted in increased angiogenesis, and repression of STC1 or FLT4 inhibited angiogenesis. The analyses of KSHV expression from KS lesions identified certain lytic genes, specifically ORF75, that were consistently expressed, and these expression patterns differed from laboratory infection of LECs with KSHV and KSHV gene expression in PEL cell lines. This study demonstrates that complex patterns of gene expression are found in KS tissue that differ from the canonical latent/lytic programs seen in KSHV cell lines and also demonstrates differences in viral gene and clinically relevant host gene expression in skin and GI KS that may offer insights into the pathogenesis of these forms of KS. One sentence summaryKaposi sarcoma that manifests in the skin and gastrointestinal tracts differ by human and viral gene expression.

microbiology↗

bioRxiv2019

HSC70 regulates cold-induced caspase-1 hyperactivation by an autoinflammation-causing mutant of cytoplasmic immune receptor NLRC4

NLRC4 is an innate immune receptor, which upon detection of certain pathogens or internal distress signal, initiates caspase-1 mediated inflammatory response. A gain-of-function mutation, H443P in NLRC4, causes familial cold autoinflammatory syndrome (FCAS) characterized by cold-induced hyperactivation of caspase-1 and inflammation. Here, we show that heat shock cognate protein 70 (HSC70) complexes with NLRC4 and negatively regulates caspase-1 activation by NLRC4-H443P. Compared to NLRC4, the structurally altered NLRC4-H443P shows enhanced interaction with HSC70. Knockdown of HSC70 or inhibition of its ATPase activity enhances caspase-1 activation by NLRC4-H443P. Exposure to subnormal temperature resulted in reduced interaction of NLRC4-H443P with HSC70, and an increase in its ability to form ASC-specks and activate caspase-1. By demonstrating that HSC70 differentially interacts with NLRC4-H443P mutant in a temperature-dependent manner to regulate caspase-1 activation, we provide a mechanism for cold-induced inflammation seen in FCAS patients with NLRC4-H443P mutation.

cell biology↗