RESUMO
Kaposi's sarcoma herpesvirus (KSHV) is an angiogenesis-inducing oncovirus whose ability to usurp the oxygen-sensing machinery is central to its oncogenicity. By upregulating the hypoxia-inducible factors (HIFs), KSHV reprograms infected cells to a hypoxia-like state, triggering angiogenesis. Here we identify a link between KSHV replicative biology and oncogenicity by showing that KSHV's ability to regulate HIF2α levels and localization to the endoplasmic reticulum (ER) in normoxia enables translation of viral lytic mRNAs through the HIF2α-regulated eIF4E2 translation-initiation complex. This mechanism of translation in infected cells is critical for lytic protein synthesis and contributes to KSHV-induced PDGFRA activation and VEGF secretion. Thus, KSHV regulation of the oxygen-sensing machinery allows virally infected cells to initiate translation via the mTOR-dependent eIF4E1 or the HIF2α-dependent, mTOR-independent, eIF4E2. This "translation initiation plasticity" (TRIP) is an oncoviral strategy used to optimize viral protein expression that links molecular strategies of viral replication to angiogenicity and oncogenesis.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Carcinogênese/patologia , Herpesvirus Humano 8/fisiologia , Hipóxia/fisiopatologia , Iniciação Traducional da Cadeia Peptídica , Sarcoma de Kaposi/patologia , Replicação Viral , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Carcinogênese/genética , Carcinogênese/metabolismo , Fator de Iniciação 4E em Eucariotos/genética , Fator de Iniciação 4E em Eucariotos/metabolismo , Humanos , Sarcoma de Kaposi/genética , Sarcoma de Kaposi/metabolismo , Sarcoma de Kaposi/virologia , Ativação ViralRESUMO
Kaposi's sarcoma (KS) is an AIDS-defining cancer caused by the KS-associated herpesvirus (KSHV). Unanswered questions regarding KS are its cellular ontology and the conditions conducive to viral oncogenesis. We identify PDGFRA(+)/SCA-1(+) bone marrow-derived mesenchymal stem cells (Pα(+)S MSCs) as KS spindle-cell progenitors and found that pro-angiogenic environmental conditions typical of KS are critical for KSHV sarcomagenesis. This is because growth in KS-like conditions generates a de-repressed KSHV epigenome allowing oncogenic KSHV gene expression in infected Pα(+)S MSCs. Furthermore, these growth conditions allow KSHV-infected Pα(+)S MSCs to overcome KSHV-driven oncogene-induced senescence and cell cycle arrest via a PDGFRA-signaling mechanism; thus identifying PDGFRA not only as a phenotypic determinant for KS-progenitors but also as a critical enabler for viral oncogenesis.