STAT3 activation contributes directly to Epstein‐Barr virus–mediated invasiveness of nasopharyngeal cancer cells in vitro

Abstract

Nasopharyngeal cancer (NPC) is an Epstein-Barr virus (EBV)-associated head and neck cancer prevalent in Asia. Although with reasons not fully understood, the intrinsic invasiveness of NPC is believed to be EBV-linked. Recently, EBV was found to induce STAT3 activation. Constitutive STAT3 activation correlated with advanced clinical staging in NPC. We hypothesized that STAT3 activation by EBV directly contributes to the intrinsic invasiveness of NPC cells. Phospho-STAT3-Tyr705 was detected in high percentage of NPC tumors (7/10 cases). Using a paired NPC cell line model, HONE-1 and the EBV-infected counterpart, HONE-1-EBV, we found that HONE-1-EBV expressed a higher level of phospho-STAT3-Tyr705 and was 11-fold more invasive than HONE-1. In HONE-1-EBV, STAT3 siRNA targeting inhibited both spontaneous and serum-induced invasion, as well as cell growth. Conversely, activation of STAT3 (by expressing an activated STAT3 mutant, namely STAT3C) in the parental HONE-1, mimicking EBV-induced STAT3 activation, significantly enhanced its invasiveness and proliferation, which was accompanied by increased expression of markers of mesenchymal status, proliferation and anti-apoptosis. Our results demonstrated that EBVinduced STAT3 activation is responsible for NPC cell proliferation and invasion. This was further confirmed by a small molecule inhibitor of JAK/STAT3, JSI-124. JSI-124 inhibited STAT3 activation in HONE-1-EBV, with subsequent growth inhibition, induction of PARP cleavage, abrogation of anchorage-independent growth and invasion. We found that EBV-independent activation of STAT3 by a growth factor, EGF, also contributed to NPC invasion. In conclusion, EBV-induced STAT3 activation directly contributes to the intrinsic invasiveness of NPC cells and STAT3 targeting may be beneficial in treating aggressive NPC. ' 2009 UICC Key words: STAT3; nasopharyngeal cancer (NPC); EBV; invasion Nasopharyngeal cancer (NPC) is a distinct type of head and neck cancer highly prevalent in Southeast Asia with a strong etiological association with the Epstein-Barr virus (EBV), a wellknown group I carcinogen. 1,2 One hundred percent of NPC cases in endemic regions are EBV positive. 3,4 NPC is also characterized by heavy lymphocyte infiltration (with rich supply of cytokines in the tumor microenvironment), high invasive and metastatic tendency. Recurrent NPC patients have high rate of distant metastasis up to 37%. [5][6][7] The underlying mechanism for its high metastatic characteristics is largely unknown. However, EBV is believed to play a major role.Signal Transducer and Activator of Transcription 3 (STAT3) is constitutively activated or overexpressed in a vast number of human cancers, including breast, lung, prostate, brain, leukemia, multiple myeloma, head and neck squamous cell carcinoma and NPC. [8][9][10][11] This pivotal transcription factor is known to be a key regulator for multiple cellular processes, including cell growth, apoptosis, metastasis, epithelial-mesenchymal transition and differentiation. STAT3 has been proposed to...

Celecoxib induces apoptosis and cell-cycle arrest in nasopharyngeal carcinoma cell lines via inhibition of STAT3 phosphorylation

“…Indeed, it is detected in more than 75% of NPC cases. Growing evidence indicates that STAT3 activation contributes to the progression and invasiveness of NPC [16][17][18] . Therefore, the activation of STAT3 provides a promising and valid target for NPC therapeutic modalities.…”

“…Accumulating evidence has demonstrated that STAT3 is a promising molecule target for anticancer treatment and cancer prevention [14,15] . More recently, STAT3 has also been found to be activated in www.chinaphar.com Liu DB et al Acta Pharmacologica Sinica npg more than 75% of NPC cases, and this molecule plays a significant role in driving NPC progression and metastasis [16][17][18] . A recent study identified celecoxib as a novel inhibitor of STAT3 [6] .…”

Epstein-Barr Virus LMP1 Activates EGFR, STAT3, and ERK through Effects on PKCδ

“…EGFR expression and STAT3 activation are elevated in NPC, and STAT3 activation is important for the invasiveness of EBV-associated NPC, which can be blocked by STAT3 inhibitor treatment (25,26). The effects of LMP1 on EGFR, STAT3 activation, and regulation of STAT3 target genes may be important factors in the development of NPC.…”

Characterization of the Nucleocytoplasmic Transport Mechanisms of Epstein-Barr Virus BFLF2

“…HONE1-EBV cells (gift from Prof. S.W. Tsao, University of Hong Kong) are EBV positive nasopharyngeal carcinoma cell lines [21], which were cultured in RPMI-1640 (Gibco-BRL) medium supplemented with 10% FBS. Mouse monoclonal antibody (mAb) anti-Flag was purchased from Abmart (Shanghai, China) and rabbit polyclonal antibody (pAb) anti-YFP was purchased from RayBiotech.…”

“…In order to explore the physiological mechanisms of EBV natural hosting cells, the EBV-latent cells (HONE1-EBV cells), which were generated by infecting human gastric adenocarcinoma cells (AGS) and HONE1 cells with recombinant EBV genomes expressing GFP [21,54], were chosen to continue the experiments. HONE1-EBV cells were transfected with expressing plasmid pFLAG-CMV-TAP, pCMV9-3×Flag-importin β1, pFlag-kα6, pFLAG-CMV-transportin-1 or pFLAG-CMV-2, and cells were induced to undergo lytic cycle activation by transfecting with pBZLF1-HA plasmid.…”