Characterization of STAT3 expression, signaling and inhibition in feline oral squamous cell carcinoma.

Megan E Brown,Chris Premanandan,Misty D Bear,Cheryl A London,William C Kisseberth,Thomas J Rosol

doi:10.1186/s12917-015-0505-7

Abstract

BackgroundSignal transducer and activator of transcription 3 (STAT3) plays a critical role in tumor development by regulating signaling pathways involved in cell proliferation, survival, metastasis and angiogenesis. STAT3 is activated in many cancers, including head and neck squamous cell carcinoma (HNSCC) in people. Feline oral squamous cell carcinoma (OSCC) is similar to advanced or recurrent HNSCC as it is poorly responsive to traditional therapies and carries a poor long-term prognosis. The purpose of this study was to characterize expression and activation of STAT3 in feline OSCC cell lines and tumor samples and to investigate the biologic activity of a novel, allosteric STAT3 inhibitor, LLL12, in feline OSCC cell lines.ResultsWe evaluated 3 feline OSCC cell lines and one of these (SCCF2) exhibited high levels of constitutive STAT3 phosphorylation and high sensitivity to LLL12 treatment. Exposure of SCCF2 cells to LLL12 resulted in decreased expression of pSTAT3 and total STAT3, apoptosis as assessed by caspase 3/7 activation, inhibition of colony formation and reduced expression of the STAT3 transcriptional target survivin. In contrast, the STAT3 transcriptional targets VEGF and MCL-1 increased after LLL12 treatment. This was, in part, likely due to LLL12 mediated upregulation of HIF-1α, which is known to drive VEGF and MCL-1 expression. The OSCC cell lines with low basal STAT3 phosphorylation did not exhibit these effects, suggesting that STAT3 inhibition was responsible for the observed results. Lastly, immunohistochemistry for pSTAT3 was performed using a feline OSCC tissue microarray, demonstrating expression in 48 % of samples tested.ConclusionsThese data demonstrate that LLL12 has biologic activity against a feline OSCC cell line expressing pSTAT3 and that STAT3 represents a target for therapeutic intervention in this disease. However, given the up-regulation of several STAT3 transcriptional targets following treatment, further investigation of STAT3 and its related signaling pathways in OSCC is warranted.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-015-0505-7) contains supplementary material, which is available to authorized users.

Highlights

Signal transducer and activator of transcription 3 (STAT3) plays a critical role in tumor development by regulating signaling pathways involved in cell proliferation, survival, metastasis and angiogenesis
Constitutive phosphorylation of STAT3 is variable in feline oral squamous cell carcinoma (OSCC) cell lines and correlates with response to LLL12 To assess whether STAT3 is constitutively activated in feline OSCC cell lines, Western blotting was performed to evaluate for the presence of phosphorylated STAT3 (pSTAT3)
Treatment with LLL12 inhibits pSTAT3 and STAT3 expression in feline OSCC cells that express elevated levels of pSTAT3 To assess the direct effects of LLL12 on pSTAT3, two OSCC cell lines with high (SCCF2) and low (SCCF3) basal STAT3 activation were chosen for further analysis

Summary

Introduction

Signal transducer and activator of transcription 3 (STAT3) plays a critical role in tumor development by regulating signaling pathways involved in cell proliferation, survival, metastasis and angiogenesis. The signal transducer and activator of transcription (STAT) family of proteins consists of seven isoforms that are transcription factors responsible for relaying signals from extracellular growth factors and cytokines, thereby influencing normal cellular physiology and development. Due to their role in cell survival, proliferation and angiogenesis, STAT proteins, in particular STAT3 and STAT5, have been implicated in cancer initiation and progression [1]. Since activating mutations of STAT3 are rare [7], constitutive phosphorylation of STAT3 is generally the result of aberrations in upstream signaling proteins or physiologic regulators [5, 8]

Objectives

Methods

Results

Discussion

Conclusion