The levels of LRG have been shown

The levels of LRG1 have been shown to be elevated in the serum and urinary exosomes of lung cancer patients (Li et al., 2011; Liu et al., 2012) with this protein also being identified in lung tumour tissue. The role of LRG1 is not fully understood, although it is of interest due to its role in angiogenesis; where it acts as a pro-angiogenic factor modulating the role of TGF-β (Wang et al., 2013). Wang and colleagues have also shown that angiogenesis can be reduced by the inhibition of LRG1 and so it is a possible therapeutic target for regulation of angiogenesis. It is known that during radiotherapy angiogenic factor Embelin Supplier is modulated with a correlative increase in angiogenesis (Sofia Vala et al., 2010; Gu et al., 2013). Therefore the finding that LRG1 is elevated in lung cancer patients with poor response to radiotherapy indicates it may have three clinical uses: as a therapeutic target to increase the efficacy of radiotherapy, as a tool to stratify patients who require angiogenesis inhibitors in combination with radiotherapy (Wang et al., 2013) and as shown in this study as a biomarker for poor prognosis.
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Role of Funding Sources This work was supported by the Cancer Research UK Experimental Cancer Medicine Centre code R114689 A07, and Swedish Cancer Society CAN2010/1335 and Leukemia Lymphoma Research code 13005. No funding source was involved in the writing of this manuscript or the decision to submit it for publication.
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Introduction OSCC is one of the most common HNSCC, with an estimated 260,000 new cases and 120,000 deaths worldwide each year (Jemal et al., 2011). Despite recent advances in diagnosis and treatment, the 5-year survival rate of patients with OSCC is no more than 50% (Panzarella et al., 2014). Over the past two decades, numerous prognostic and predictive markers for clinical outcomes in OSCC have been proposed (Ratajczak-Wrona et al., 2013); however, few have been applied in clinical practice due to the non-reproducibility of the initial findings (Choi and Myers, 2008; Principe et al., 2013). To date, the classical clinic pathological parameters of tumor such as primary site, tumor stage, lymph nodal stage and clinical TNM stage remain the most significant factors to affect outcome of patients with OSCC. However, it is impossible to predict patients at a high risk of death mainly based on these parameters. Therefore, it is critical to identify novel and effective prognostic predictors and therapeutic targets for treating this common malignancy. In eukaryotic cells, proteasomes play an essential role in intracellular proteolysis and are involved in the control of most biological processes through regulated degradation of key proteins. PA28 is a member of a unique family of proteasomal activators that has the ability to stimulate the proteolytic activity of the 20S core proteasome independent of ubiquitination and ATP (Li et al., 2007). Unlike PA28α and PA28β, PA28γ (also known as Ki antigen, 11Sγ, or REGγ) localizes in the nucleus and forms a homo-heptamer (Kloetzel and Ossendorp, 2004; Rechsteiner et al., 2000; Rivett and Hearn, 2004). PA28γ, regulated by MEKK3, B-RAF, caspase-3/7 and targeted by miR-7-5p, is a multifunctional protein that is involved in the degradation of important regulatory proteins, such as SRC-3, PTTG1 and cyclin-dependent kinase inhibitors p21/16/19 in an ubiquitin- and ATP-independent manner, and has been implicated in the regulation of cell cycle progression (Li et al., 2007; Araya et al., 2002; Chen et al., 2007; Ying et al., 2006; Shi et al., 2015). Moreover, PA28γ-deficient mice have been shown to exhibit growth retardation (Barton et al., 2004). Several targets of PA28γ have been identified in recent years, suggesting that it plays important roles in angiogenesis, hepatic lipid metabolism, infectious diseases and premature aging (Liu et al., 2014; Dong et al., 2013; Yan et al., 2014; Li et al., 2013). PA28γ is over-expressed in some cancer tissues, suggesting that this protein may also have a potential role in tumorigenesis (Wang et al., 2011; Roessler et al., 2006). Some studies found that PA28γ may facilitate the turnover of the tumor suppressor p53 by promoting murine double minute 2 (MDM2)-mediated p53 ubiquitination (He et al., 2012; Zhang and Zhang, 2008) and PA28γ could take part in the ATM-DBC1-SIRT1 axis induced p53-dependent apoptosis (Magni et al., 2014). Recently researchers found that mutant p53 (p53-R248Q) could up-regulate PA28γ in endometrial cancer (Wang et al., 2015), thus, there is an auto-regulatory feedback loop between p53 and PA28γ (Wan et al., 2014). Nevertheless, the mechanism by which PA28γ exerts its effects on tumor cells remains unclear.