INTERPLAY BETWEEN KSHV VIRAL EXPRESSION AND PDGF RECEPTOR-ALPHA EXPRESSION AND PDGFRA AS A THERAPEUTIC TARGET IN KSHV-ONCOGENESIS

JULIÁN NAIPAUER; LUCAS CAVALLIN; QI MA; SACHIN GUPTA; ENRIQUE MESRI

Miami

Workshop; 18th International Workshop on KSHV and Related Agents; 2015

Background: Kaposi's sarcoma (KS), an AIDS-defining cancer caused by the KS herpesvirus (KSHV), is a vascular sarcoma characterized by intense angiogenesis and spindle cell proliferation. Key pending questions on KS are its cellular ontology and the molecular mechanisms of viral oncogenesis. Defining which are the critical host pathways subverted by viral infection to induce oncogenesis is essential to understand viral pathogenesis and to identify potential therapeutic targets. Receptor tyrosine kinase proteomic arrays of KSHV-induced mouse tumors, together with pharmacologic and genetic studies identified activated PDGF receptor-alpha (PDGFRα) as the predominant oncogenic signaling in KS. We sought to determine the molecular basis of the PDGFRA / KSHV interplay and its occurrence in KS lesions.Methods and Results: PDGFRα expression is upregulated in mECK36 cells upon starvation and this upregulation seems to be transcriptionally dependent. When mECK36 cells lose the KSHV episome in vitro prior to their growth in vivo, they completely lose tumorigenicity, and also lose their capacity of PDGFRα expression upregulation upon starvation. Using a tetracycline-inducible RTA (TET-RTA) mECK36 cell line for lytic induction with tetracycline, we show down-regulation of PDGFRα expression and an increase in PDGFRα mRNA stability upon lytic induction. Our data points to the existence of an interplay between KSHV viral expression and PDGF receptor-alpha expression and activation which is essential for KS tumor growth, pointing to this oncogenic mechanism as a potential KS target. IHC analysis of a collection of KS biopsies and controls contained in a tissue microarray developed by the AIDS Cancer Specimen Repository (ACSR) showed in the vast majority of the 70 skin KS biopsies tested that areas that stained strongly for phosphorylated PDGFRA also stained for nuclear KSHV-LANA. We also analyzed a TMA containing the biopsies from the Phase II AIDS-KS trial for Gleevec/Imatinib, a multi-kinase inhibitor that target the PDGFRs, (Phase II trial of imatinib in AIDS-associated Kaposi´s sarcoma: AIDS Malignancy Consortium Protocol 042) showing a robust PDGFRα phosphorylation which colocalized with PDGFA, PDGFB and KSHV-LANA. Moreover, six of the nine biopsies that presented high phospho-PDGFRA and LANA staining also show strong staining for at least one of the PDGFRA ligands. ConclusionsOur results show an interplay between KSHV and PDGFRA activation that is critical for KS tumor development in mice. The occurrence of this mechanism of PDGFRA activation in KS show that phosphorylated PDGFRA can be the target of Imatinib/ Gleevec in KS treatment and for other rational KS therapies.