Exosomal HIF1α supports invasive potential of nasopharyngeal carcinoma-associated LMP1-positive exosomes

Abstract

It has emerged recently that exosomes are potential carriers of pro-tumorigenic factors that participate in oncogenesis. However whether oncogenic transcription factors are transduced by exosomes is unknown. Hypoxia-inducible factor-1alpha (HIF-1α) transcriptionally regulates numerous key aspects of tumor development and progression by promoting a more aggressive tumor phenotype, characterized by increased proliferation and invasiveness coupled with neoangiogenesis. It has been shown that the principal oncoprotein of Epstein-Barr Virus (EBV), Latent Membrane Protein 1 (LMP1), drives oncogenic processes and tumor progression of the highly invasive EBV malignancy, nasopharyngeal carcinoma (NPC). We now demonstrate that endogenous HIF-1α is detectable in exosomes, and that LMP1 significantly increases levels of HIF-1α in exosomes. HIF-1 recovered from exosomes retains DNA-binding activity and is transcriptionally active in recipient cells after exosome uptake. We show also that treatment of EBV-negative cells with LMP1-exosomes increases migration and invasiveness of NP cell lines in functional assays, which correlates with the phenotype associated with Epithelial Mesenchymal Transition (EMT). In addition we provide evidence that HIF1α itself participates in exosome-mediated pro-metastatic effects in recipient cells, since exosome-mediated delivery of active and inactive forms of HIF-1α results in reciprocal changes in expression of E- and N-cadherins associated with EMT. Further, immunohistochemical analysis of NPC tumor tissues revealed direct correlation between protein levels of LMP1 and of the endosome/exosome marker tetraspanin, CD63, which suggests an increase in exosome formation in this EBV-positive malignancy. We hypothesize that exosome-mediated transfer of functional pro-metastatic factors by LMP1-positive NPC cells to surrounding tumor cells promotes cancer progression.

Exosomes as the Promising Biomarker for Epstein-Barr Virus (EBV)-Associated Cancers

“…In addition, the level of LMP1 is highly correlated with CD63 expression [19]. This suggests that LMP1 may upregulate the exosomal secretion, hence promoting the EBV-associated cancers [19]. As summarized in Table 1, cumulative findings suggest that exosomal LMP1 promotes the growth and progression of EBV-associated cancers.…”

“…This interaction facilitates the former to escape lysosomal degradation [33] which may result in enhanced oncogenicity of exosomal LMP1. In addition, the level of LMP1 is highly correlated with CD63 expression [19]. This suggests that LMP1 may upregulate the exosomal secretion, hence promoting the EBV-associated cancers [19].…”

“…Latency type II, on the other hand, results in the expression of LMP1, LMP2 and EBNA1 as seen in HL and NPC, whereas in latency type III, all latent proteins/antigens are expressed in the course of acquired immune deficiency syndrome (AIDS)-related lymphomas and lymphoblastoid cell lines (LCLs) [17,18]. Of note, the LMPs-carrying exosomes have been previously shown to be secreted by EBV-infected cells particularly the NPC cells [19][20][21].…”

“…This consequently resulted in the immune escape of tumour cells, and hence promoting the cancer growth and progression [24]. Exosomes containing LMP1 and HIFα have also been demonstrated to induce tumour invasion in NPC [19]. Moreover, LMP1 …”

“…[20], EGFR [30], HIF1α [19], ICAM1 [21], FGF2 [25], chemokine (C-C motif) ligand 20 (CCL20) [22], dUTPase [48] and interleukins (ILs)/caspase 1/interferon-inducible protein 16 (IFI16) [49] ( Table 1).…”