International Journal of Radiation Oncology*Biology*Physics
Biology ContributionRadiosensitization by Inhibiting STAT1 in Renal Cell Carcinoma
Introduction
Renal cell carcinoma (RCC) has been historically regarded as a radioresistant malignancy. Conventional radiotherapy (1.8–2.0 Gy/d) was thought to have little use in the management of primary kidney cancer in terms of cure. In patients with metastatic disease, conventional radiotherapy is effective in palliation of symptoms, but it results in a subjective or objective response in only 50% of patients. Thus, it is imperative to understand the molecular mechanism underlying this radioresistance. Basic mechanisms of signal transduction and DNA repair after irradiation have been studied in simple genetic model systems and in cells derived from radiosensitive patients with genetic disorders such as ataxia telangiectasia 1, 2. Although these investigations have elucidated important basic principles and pathways of the response of eukaryotic cells to radiation damage, a significant effect on clinical management requires more preclinical application or translational studies. Continuing exploration of radioresistance targets in tumors and their manipulation to improve radiotherapy is thus needed.
Renal cell carcinoma is a histologically heterogeneous disease. Several subtypes of RCC have been described, including clear cell, papillary, chromophobe, collecting duct, and unclassified, which did not fit with any other diagnosis. Clear cell RCC is the most common subtype (75–80%), followed by papillary RCC (10–15%) and chromophobe (4–6%). In addition, rarer types of RCC have been morphologically defined, including renal medullary RCC, Xp11 translocation carcinoma, carcinoma associated with neuroblastoma, mucinous tubular carcinoma, and spindle cell carcinoma. Each subtype appears to have a distinct molecular signature reflecting their differences, not only in morphology, but also in biology and clinical behavior (3).
Recently, signal transducer and activator of transcription 1 (STAT1), a transcription factor downstream of the interferon-signaling pathway, has been implicated in the presence of radioresistance, first demonstrated in a head-and-neck cancer cell line (4). To date, its involvement in RCC in general and its specific relationship with radioresistance in RCC have never been explored. Using our extensive microarray gene expression data (5), we examined the level of STAT1 expression in the two most common subtypes of RCC (i.e., clear cell and papillary). Immunohistochemistry of STAT1 and phosphorylated STAT1 were performed on RCC tissue arrays to validate the microarray data. We then studied the expression level of STAT1 and the cellular effects and response to radiation on two representative cell lines of each subtype after STAT1 inhibition, both by RNAi and fludarabine, a nucleoside analog used as a chemotherapeutic agent that can reduce the level of STAT1 protein. Finally, we examined the expression of signal transducer and activator of transcription 3 (STAT3) in both human RCC and the cell lines to establish whether the known relationship between STAT1 and STAT3 exists in human RCC and whether the radioresistant effect is related to either STAT1 or STAT3 or a combination.
Section snippets
Examination of STAT1 expression in RCC vs. normal kidney using microarray gene expression database
We compared the expression of STAT1 and STAT3 in clear cell and papillary RCC and normal kidney tissue samples using our extensive gene expression profiling database of renal tumors (5). For this study, 164 clear cell and 47 papillary RCC samples and 15 normal kidney samples were included.
Immunohistochemistry
Paraffin tissue blocks from 34 clear cell RCC samples (30 conventional and 4 with sarcomatoid features) and 12 normal adjacent kidney tissue samples were studied, and tissue microarray analysis was performed.
STAT1 differentially overexpressed in human RCC by microarray analysis
The STAT1 expression data in human clear cell and papillary RCC and in corresponding normal renal tissues is shown in Fig. 1A. The mean and standard errors for STAT1 gene expression were calculated. A two-tailed Student's t test was calculated, and the difference was determined to be statistically significant at the 95% confidence interval (p = 1.5 × 10−8 for clear cell and p = 3.6 × 10−4 for papillary). This is the first study to report the overexpression of STAT1 in human RCC. No elevation
Discussion
Renal cell carcinoma is traditionally considered to be radioresistant. The failure in treating tumors by radiotherapy has been ascribed to intrinsic tumor cell radioresistance and tumor microenvironmental factors, such as hypoxia, which favors tumor cell survival after irradiation 8, 9. An understanding of the molecular mechanisms underlying tumorigenesis and the cancer cell response to external factors, including irradiation, is necessary to develop more rational and effective treatment. A
Acknowledgments
We thank the Cooperative Human Tissue Network of the National Cancer Institute for providing the renal tumor cases. We also thank David Nadziejka for proofreading and Sabrina Noyes for manuscript preparation and submission.
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2018, Bulletin du CancerCurcumin enhances the radiosensitivity of renal cancer cells by suppressing NF-κB signaling pathway
2017, Biomedicine and PharmacotherapyCitation Excerpt :In order to improve the therapeutic efficiency and reduce the damage to adjacent normal tissues in cancer treatment, the radiotherapy are always combined with agents to increase cytotoxicity or radiosensitivity. Since the therapeutic effect of radiation for patients with RCC is rarely satisfactory, it is imperative to discover novel and potential radiosensitizer to increase the efficacy of palliative radiotherapy [17]. Curcumin has been reported to be involved in the radiosensitivity enhancement in several cancer cells such as colorectal cancer, prostate cancer, and hepatocellular carcinoma [18,19].
Biological determinants of radioresistance and their remediation in pancreatic cancer
2017, Biochimica et Biophysica Acta - Reviews on CancerCitation Excerpt :While in some instances STAT1 can increase apoptosis through the activation of pro-apoptotic genes and suppression of anti-apoptotic proteins produced by the NF-κB pathway, its constitutive overexpression has also been shown to promote cell survival likely via the modulation of pathways activated by ATM, including Chk2 and NBS1 [148–150]. This overexpression of STAT1, which is often seen in cancers, is likely linked to their observed radioresistance as knockdown of STAT1 has been shown to increase radiosensitivity in the cells of squamous cell carcinoma [148] and in renal cell carcinoma [145]. Researchers have suggested that this radiosensitization is a result of the modulation of IL-6 and IL-8 as the expression of these cytokines greatly diminishes following the downregulation of STAT1 [144].
Radiotherapy in the age of cancer immunology: Current concepts and future developments
2017, Critical Reviews in Oncology/HematologyCitation Excerpt :Despite the simplistic view of STAT1 as an immunogenic signalisation pathway in antagonistic relationship with immunosuppressive STAT3, its role in the modulation of antitumor immune response is quite ambiguous: STAT1 activation in tumor-associated macrophages lead to T-lymphocytes apoptosis and restrain specific immune activation (Kusmartsev and Gabrilovich, 2005). Moreover, STAT1 expression is regarded as an intrinsic factor of radioresistance in renal cancer cells that can be inhibited both by zoledronic acid (Kijima et al., 2013) and fludarabine (Hui et al., 2009). STAT3, that is constitutively activated in 70% of solid tumors (Pensa et al., 2008) abort immune response mainly by inhibiting the maturation of antigen presenting cells (APCs), accounting for impaired DC-mediated induction of T cell responses (Yu et al., 2007), recruitment of MDSCs and Tumor-associated Macrophages (TAM2) with acquisition of a M2 phenotype (see dedicated paragraph below).
Reciprocal regulation of hypoxia-inducible factor 2α and GLI1 expression associated with the radioresistance of renal cell carcinoma
2014, International Journal of Radiation Oncology Biology Physics
Supported by a research grant from the Methodist Hospital Research Institute, and also the Gerber Foundation, Hauenstein Foundation, Michigan Economic Development Corporation, and Michigan Technology Tri-Corridor to B. T. Teh. Supported by National Natural Science Foundation of China for Young Scholar (30800280) to Z. Hui.
Presented in part at the 48th Annual Meeting of the American Society for Therapeutic Radiology and Oncology, November 5–9, 2006, Philadelphia, PA.
Conflict of interest: none, except B. S. Teh received a Methodist Hospital Research Institute research grant.