Original ArticlesPA28γ acts as a dual regulator of IL-6 and CCL2 and contributes to tumor angiogenesis in oral squamous cell carcinoma
Introduction
Oral squamous cell carcinoma (OSCC) is one of the most common human head and neck cancers. Currently, the morbidity and mortality rates of OSCC remains high in most countries. PA28γ (also known as REGγ, Ki or PSME3), a member of the 11S proteasome activator family, binds and activates 20S proteasomes [1,2]. Activated PA28γ degrades several important regulatory proteins, such as SRC-3 [3], PTTG1 [4], hepatitis C virus core protein [5] and p21/16/19 [2,6,7]. In addition, PA28γ inhibits the activity of the tumor suppressor p53 by promoting its cellular distribution and mouse double minute 2 homolog (MDM2)-mediated degradation [8,9]; meanwhile, p53 suppresses PA28γ expression, and mutant p53 (p53-R248Q and p53-R175H) upregulates PA28γ expression [10,11]. PA28γ affects multiple apoptotic hallmarks, including p53 phosphorylation and caspase activation [12,13]. Moreover, PA28γ is required for DNA repair and chromosomal stability [14,15].
PA28γ is reported to be overexpressed in OSCC [16,17], thyroid [18], colorectal [19], breast [20] and lung and liver cancers [21]. In addition, PA28γ is associated with metastasis and poor prognosis in patients with breast cancer [20]. Our previous study showed that PA28γ is a good predictor for the risk of death in OSCC and that PA28γ promotes the proliferation, migration and invasion of OSCC cells in vitro and in vivo [16]. In addition, we found that the tumor microvascular density in PA28γ-silenced nude mice with a subcutaneous transplantation of tumor cells was less than that in the control group, suggesting that PA28γ might be associated with OSCC tumor angiogenesis. However, the molecular mechanisms underlying this phenomenon have not been investigated.
In this study, we verified that PA28γ promoted tumor angiogenesis, and PA28γ silencing significantly suppressed tumor angiogenesis using a co-culture model and a subcutaneous xenotransplantation tumor model. Further experiments showed that PA28γ stimulated tumor angiogenesis via a dual regulation of IL-6 and CCL2 expression. This study not only helped us to understand the basic biological processes of OSCC tumorigenicity and metastasis but also provided some new ideas and lay the foundation for the development of new tumor immunotherapy strategies, which target PA28γ based on the “double” regulation of IL-6 and CCL2.
Section snippets
Cell culture
HSC-3 cells were purchased from the Cell Bank of Japanese Collection of Research Bioresource (JCRB, Shinjuku, Japan). HN31 cells were provided by Dr. J. Silvio Gutkind (Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health). The 293T lines were purchased from the American Type Culture Collection (Manassas, VA, USA). The HUVECs were provided by Dr. Xikun Zhou (State Key Laboratory of Biotherapy, Collaborative Innovation Center
PA28γ promotes OSCC cells to recruit endothelial cells and induce angiogenesis in vitro
To investigate the biological function of PA28γ during angiogenesis in OSCC, we established stable PA28γ-expressing HSC-3 and HN31 cell lines using lentivirus (Fig. 1A and Fig. S1). Then, we investigated endothelial cell migration and invasion after co-culturing with conditioned media derived from the indicated PA28γ differentially expressed OSCC cells. We observed that silencing PA28γ inhibited, whereas overexpressing PA28γ strongly provoked, the abilities of both the HSC-3 and HN31 cells to
Discussion
Tumor growth is a complicated biological process, and blood vessels are necessary for supplying nutrients and oxygen to the tumor [25]. Tumor angiogenesis is critical for tumor growth, maintenance, and metastasis [26,27]. Many studies demonstrate that angiogenesis inhibitors have a significant therapeutic value [28,29]. Recently, PA28γ was reported as a novel angiogenic factor that plays an important role in the VEGF-induced expression of VCAM-1 and E-Selectin by antagonizing PKA signaling [30
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Nos. 81672675, 81621062 and 81472533), the 111 Project of MOE China (Grant No. B14038), and the Open Foundation of State Key Laboratory of Oral Diseases, Sichuan University (SKLOD201802, SKLOD201701, and SKLOD201714).
Conflicts of interest
The authors declare no potential conflicts of interest.
References (37)
- et al.
Purification of an 11 S regulator of the multicatalytic protease
J. Biol. Chem.
(1992) - et al.
Ubiquitin- and ATP-independent proteolytic turnover of p21 by the REGgamma-proteasome pathway
Mol. Cell
(2007) - et al.
The SRC-3/AIB1 coactivator is degraded in a ubiquitin- and ATP-independent manner by the REGgamma proteasome
Cell
(2006) - et al.
Ubiquitin-independent degradation of cell-cycle inhibitors by the REGgamma proteasome
Mol. Cell
(2007) - et al.
Mutant p53 (p53-R248Q) functions as an oncogene in promoting endometrial cancer by up-regulating REGgamma
Canc. Lett.
(2015) - et al.
Identification of PSME3 as a novel serum tumor marker for colorectal cancer by combining two-dimensional polyacrylamide gel electrophoresis with a strictly mass spectrometry-based approach for data analysis
Mol. Cell. Proteomics
(2006) - et al.
Double antiangiogenic protein, DAAP, targeting VEGF-A and angiopoietins in tumor angiogenesis, metastasis, and vascular leakage
Canc. Cell
(2010) - et al.
Bevacizumab plus oxaliplatin-based chemotherapy as adjuvant treatment for colon cancer (AVANT): a phase 3 randomised controlled trial
Lancet Oncol.
(2012) - et al.
Antiangiogenic therapy in oncology: current status and future directions
Lancet
(2016) - et al.
PKA turnover by the REGgamma-proteasome modulates FoxO1 cellular activity and VEGF-induced angiogenesis
J. Mol. Cell. Cardiol.
(2014)
Associations between proteasomal activator PA28gamma and outcome of oral squamous cell carcinoma: evidence from cohort studies and functional analyses
EBioMedicine
Interleukin-6: an angiogenic target in solid tumours
Crit. Rev. Oncol. Hematol.
Inhibition of TGF-beta/SMAD3/NF-kappaB signaling by microRNA-491 is involved in arsenic trioxide-induced anti-angiogenesis in hepatocellular carcinoma cells
Toxicol. Lett.
Endothelial CCR2 signaling induced by colon carcinoma cells enables extravasation via the JAK2-Stat5 and p38MAPK pathway
Canc. Cell
Aberrant accumulation of PTTG1 induced by a mutated thyroid hormone beta receptor inhibits mitotic progression
J. Clin. Invest.
Proteasome activator PA28gamma-dependent nuclear retention and degradation of hepatitis C virus core protein
J. Virol.
ARF regulates the stability of p16 protein via REGgamma-dependent proteasome degradation
Mol. Canc. Res. MCR
Proteasome activator PA28 gamma regulates p53 by enhancing its MDM2-mediated degradation
EMBO J.
Cited by (0)
- 1
Contributed equally.