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 Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 1  |  Issue : 6  |  Page : 183-187

Galanin is a novel epigenetic silenced functional tumor suppressor in renal cell carcinoma


1 Department of Urology, Chinese PLA General Hospital, Beijing, China
2 Cipher Ground, North Brunswick, NJ, USA

Date of Submission15-Nov-2015
Date of Acceptance15-Dec-2015
Date of Web Publication30-Dec-2015

Correspondence Address:
Yingduan Cheng
Cipher Ground, 675 Rt. 1 South, North Brunswick, NJ 08902
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2395-3977.172861

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  Abstract 

Aim: To assess the expression level and function of Galanin in renal cell carcinoma (RCC).
Methods: The expression level of Galanin in a series of RCC cell lines (769P, 786-O, A498, Caki-1, and ACHN) was studied. 786-O cells were exposed to pharmacological demethylation to assess the involvement of promoter methylation downregulation of Galanin level. Galanin normal expressed ACHN cell line was knockdown with siRNA and was further used to study its role in cell proliferation and invasion. The downstream targets were screened by real time-polymerase chain reaction.
Results: Galanin was downregulated in two (786-O and A498) out of five RCC cell lines. Pharmacological demethylation restored the Galanin expression to normal levels in 786-O cells suggesting of its downregulation through promoter methylation. Knockdown of Galanin resulted in increased proliferation and invasion ability of ACHN cells while increasing the expression of oncogenes MYC, CCND1, and FRA1.
Conclusion: The above results suggest that Galanin behaves as a tumor suppressor gene in RCC and may be of clinical importance as a potential biomarker and therapeutic target in renal cancer patients.

Keywords: Galanin, renal cell carcinoma, tumor suppressor gene


How to cite this article:
Sun S, Xu A, Yang G, Cheng Y. Galanin is a novel epigenetic silenced functional tumor suppressor in renal cell carcinoma. Cancer Transl Med 2015;1:183-7

How to cite this URL:
Sun S, Xu A, Yang G, Cheng Y. Galanin is a novel epigenetic silenced functional tumor suppressor in renal cell carcinoma. Cancer Transl Med [serial online] 2015 [cited 2019 Mar 20];1:183-7. Available from: http://www.cancertm.com/text.asp?2015/1/6/183/172861

Shengkun Sun and Axiang Xu have contributed equally to this article and were co-first authors



  Introduction Top


Renal cell carcinoma (RCC) is one of the most malignant tumors affecting humans. In 2013, alone more than 350,000 people were diagnosed of this disease worldwide; with more than 140,000 deaths per year.[1] With a male-to-female ratio of 1.5:1, the incidence rate of RCC is higher in men than in women. Looking at the age distribution, it shows that about 75% of patients are over 60 years old, reaching a plateau around 70–75 years while the disease is rare under 50 years of age.[2] The risk factors for this disease include smoking tobacco, hypertension, and obesity.[1] With the development and continuous progress in therapeutic strategies, the 5-year survival rates, from diagnosis, increased from 50% in 1975–1977 to 73% in 2003–2009.[3]

The development of RCC from a normal cell is a complex and multi-step process with the involvement of multiple oncogenes, tumor suppressor genes (TSGs), and signaling transduction pathways.[4],[5] Disruption of normal genetic and epigenetic patterns will result in uncontrolled balance between cell proliferation and cell death, leading to tumorigenesis in vivo.[4] Currently, it is well-accepted that epigenetic alterations precede genetic changes during tumorigenesis.[4] Promoter methylated TSGs could function as diagnostic biomarker and therapeutic targets in cancer.[5],[6],[7],[8],[9],[10] More and more promoter methylated TSGs have been reported to be involved in the tumorigenesis of RCC.[11],[12],[13],[14] Such genes not only provide the novel insights for the tumorigenesis of this malignant disease but also serve as potential therapeutic targets for RCC.

Galanin is a 30 amino acid peptide widely expressed in the central and peripheral nervous system,[15],[16] and signals through Galanin receptor 1 (GALR1), GALR2, and GALR3.[17] It is involved in many physiological functions such as metabolism, feeding, and body weight control.[18] There are few reports that suggest Galanin functions as a tumor suppressor by inhibiting the proliferation and inducing apoptosis in colon carcinoma cell line.[19],[20] The tumor suppressive function of Galanin and its receptors was also reported in head and neck squamous cell carcinoma (HNSCC), where Galanin and its receptors were silenced by DNA methylation which correlated to the poor prognosis of patients.[21],[22] Interestingly, the oncogenic role of Galanin was also reported in lung and pituitary cancer conditions.[17],[23] In this study, we evaluated the correlation of Galanin with RCC condition.


  Methods Top


Cell culture and transfection

A series of RCC cell lines (769P, 786-O, A498, Caki-1, and ACHN) and an immortalized human embryonic kidney cell line - HEK293T were cultured in Dulbecco's Modified Eagle Medium supplemented with 10% fetal bovine serum and 1% penicillin/streptomycin in a humidified chamber maintained at 37°C and 5% CO2. Control siRNA and siGalanin were purchased from Santa Cruz Biotechnology (Dallas, TX, USA). The ACHN cells were transfected with siRNA/siGalanin using RNAiMAX (Invitrogen, Eugene, OR, USA), following the manufacturer's protocol.

Pharmacological demethylation

The protocol of 5-Aza-2'-deoxycytidine (Aza) treatment was performed as previously described.[5],[24] In brief, 786-O cells (1 × 105/mL) were allowed to grow overnight. The cell culture medium was then replaced with fresh medium containing 50 μmol/L Aza for every 24 h, for three consecutive days. Cells were then harvested for RNA extraction.

RNA extraction and semi-quantitative reverse transcription polymerase chain reaction

RNA extraction was performed using trizol reagent as per manufacturer's protocol (Invitrogen, Eugene, OR, USA). The cDNA was synthesized using Random hexamers and SuperScript-III (Invitrogen, Eugene, OR, USA). Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was performed for 32 cycles with hot-start Go-Taq, according to manufacturer's protocol (Promega, Madison, WI, USA).

Growth curve and invasion assay

ACHN cells at an appropriate density in six-well plates were transfected with control siRNA or siGalanin through RNAiMax. The cell numbers were counted at 0 h, 24 h, and 48 h after transfection. For invasion assay, 1 × 105 cells in serum-free medium were seeded to the upper chamber of each insert (BD Biosciences, San Jose, CA, USA) while the lower chamber was supplemented with medium containing 1% serum. After 48 h, the migrated cells on the lower surface of the membrane were fixed in methanol for 5 min and then stained with 0.1% crystal violet. After staining, cell numbers per microscopic image field were counted to compare the invasion ability. Each experiment was conducted in triplicate in three independent experiments.

Real time-polymerase chain reaction

All primers used are listed in [Table 1]. Quantitative real-time PCR was carried out with the iQ5 Multicolor real-time PCR Detection System (Bio-Rad, Hercules, CA, USA) using real-time PCR Master Mix (SYBR Green). Each experiment was conducted in triplicate in three independent experiments.
Table 1: Sequences of primers used in this study

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Statistical analysis

Data are presented as mean ± standard deviation. Statistical assessments were carried out using Student's t test. P < 0.05 was considered statistically significant.


  Results Top


Expression profile of Galanin in renal cell carcinoma cells

We first detected the expression profile of Galanin in a series of RCC cells and an immortalized human renal epithelial cell line HEK293T [Figure 1]a. By semi-quantitative RT-PCR, we found normal Galanin expression in 769P, Caki-1, ACHN, and HEK293T, but silenced in 786-O and A498 cell lines. This tumor specific silenced pattern suggested that Galanin is a potential candidate TSG for RCC.
Figure 1. (a) Expression profile of Galanin in a series of renal cell carcinoma cells. GAPDH was used as an internal control. (b) Pharmacological demethylation restored the expression of Galanin in 786-O cells

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Pharmacological demethylation restored Galanin expression in renal cell carcinoma cell

To check if promoter methylation played a role in the downregulation of Galanin, we treated Galanin silenced cells (786-O) with DNA methyltransferase inhibitor Aza. We found that Galanin expression was restored after 3 days of Aza treatment in 786-O cells suggesting the involvement of DNA methylation in the downregulation of Galanin [Figure 1]b.

Knockdown of Galanin increased renal cell carcinoma invasion and proliferation

The tumor-specific silencing of Galanin in RCC indicated that Galanin might function as a tumor suppressor in RCC. Here, we choose ACHN cell line which exhibited normal Galanin expression for functional study. We found that downregulation of Galanin greatly elevated the invasion ability of ACHN cells, which suggested that Galanin is a negative regulator of cell invasion in RCC [Figure 2]a and [Figure 2]b.
Figure 2. (a and b) Knockdown of Galanin increased the cell invasion ability in ACHN cell. (c) Inhibition of Galanin increased cell proliferation rate in ACHN cells (**P < 0.01)

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Galanin knockdown ACHN cells were further examined for their proliferation abilities. We counted the cell number at 0 h, 24 h, and 48 h after transfection. The results showed that the proliferation rate was significantly higher in siRNA treated group compared to control cells [Figure 2]c, indicating that Galanin could inhibit cellular proliferation in ACHN cells.

Galanin function as a tumor suppressor gene by regulating MYC, CCND1, and FRA1 expression

To test how Galanin affects this increased cell invasion and proliferation, we tested the mRNA levels of the following critical factors: MYC, CCND1, FRA1, PIK3CA, MDM2, JUN, and p57, which are associated with invasion, proliferation, or apoptosis. We found that knockdown of Galanin significantly increased mRNA levels of MYC [Figure 3]a, CCND1 [Figure 3]b, and FRA1 [Figure 3]c, with little effect on PIK3CA [Figure 3]e], MDM2 [Figure 3]f, JUN [Figure 3]g, and p57 [Figure 3]h; downregulation of Galanin [Figure 3]d was also confirmed by real-time PCR. This suggested that Galanin could regulate cell invasion and proliferation by modulating mRNA levels of MYC, CCND1, and FRA1.
Figure 3. Real time polymerase chain reaction results of the screening of several critical factors in ACHN cells (**P < 0.01)

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  Discussion Top


Most RCCs are diagnosed in the advanced metastatic stage, resulting in a dramatic decrease in patient survival. The investigation of the underlying mechanism involved in its progression is critical for developing a better therapy for RCC patients. In this study, we found that Galanin is one of the silenced functional TSGs in RCC. Galanin is a 30 amino acid neuropeptide [15],[16] which activates the GALR1, GALR2, and GALR3 and stimulates numerous signal transduction and integration pathways.[21],[25],[26] There are several kinds of neuropeptides in humans, some of which have tumor suppressor functions with tumor specific hypermethylated pattern. For example, tachykinin-1 gene, which encodes the neuropeptides substance P, neurokinin A, and neuropeptide K and γ, was reported to be hypermethylated in esophageal squamous cell carcinoma and colon cancer and was associated with poor prognosis in such patients.[27],[28],[29]Somatostatin was also found frequently methylated in human esophageal adenocarcinoma and colon cancer.[27],[29] The tumor-specific methylation pattern and tumor suppressive function of Galanin and its receptors were also reported in head and neck cancer.[21],[22] These suggested that neuropeptide genes could function as tumor suppressors and serve as potential biomarkers in multiple cancers.

In this study, we found Galanin was methylated in two of the assessed RCC cell lines but not in immortalized human embryonic kidney HEK293T cells. Downregulation of Galanin increased the invasion potential and proliferation rate of ACHN cells. All these results suggested that Galanin is a novel functional TSG in RCC. We further investigated how Galanin mediated the invasion and proliferation in RCC. We tested several critical factors which were involved in tumorigenesis. We found that knockdown of Galanin could significantly upregulate mRNA levels of MYC, CCND1, and FRA1. MYC is an oncogene that contributes to the genesis of multiple cancers. This oncoprotein could promote proliferation, cell survival, genetic instability, invasion, and angiogenesis of cancer cells including RCC.[30],[31],[32] CCND1 is a critical cell cycle regulator which binds with cyclin-dependent kinases, and subsequently phosphorylates tumor suppressor protein Rb.[33] Despite its well-known role in cell cycle regulation, the effect of CCND1 on cell migration was also reported.[32],[34],[35] FRA1 (also named as FOSL1) is a member of FOS family. This family can dimerize with proteins of the JUN family, thereby forming the transcription factor complex AP-1. FRA-1 can promote cell proliferation, invasiveness, and motility.[36],[37] Our data suggested that Galanin could regulate cell proliferation and invasion by targeting MYC, CCND1, and FRA1. Underlying molecular mechanisms of how Galanin regulates the expression of MYC, CCND1, and FRA1 in RCC cells needs further assessments.

In conclusion, we have identified Galanin as a potential TSG in RCC, which is silenced by DNA methylation. Galanin inhibits cell proliferation and invasion by targeting MYC, CCND1, and FRA1 oncogenes and could serve as a novel therapeutic target for treating RCC.

Financial support and sponsorship

This study was supported by a grant from the National Natural Science Foundation of China (No. 30600613).

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Capitanio U, Montorsi F. Renal cancer. Lancet 2015. pii: S0140-673 (15) 600046-X.  Back to cited text no. 1
    
2.
Qayyum T, Oades G, Horgan P, Aitchison M, Edwards J. The epidemiology and risk factors for renal cancer. Curr Urol 2013; 6 (4): 169–74.  Back to cited text no. 2
    
3.
Siegel R, Ma J, Zou Z, Jemal A. Cancer statistics, 2014. CA Cancer J Clin 2014; 64 (1): 9–29.  Back to cited text no. 3
    
4.
Coleman WB, Tsongalis GJ. Molecular mechanisms of human carcinogenesis. EXS 2006; (96): 321–49.  Back to cited text no. 4
    
5.
Cheng Y, Geng H, Cheng SH, Liang P, Bai Y, Li J, Srivastava G, Ng MH, Fukagawa T, Wu X, Chan AT, Tao Q. KRAB zinc finger protein ZNF382 is a proapoptotic tumor suppressor that represses multiple oncogenes and is commonly silenced in multiple carcinomas. Cancer Res 2010; 70 (16): 6516–26.  Back to cited text no. 5
    
6.
Shu XS, Li L, Ji M, Cheng Y, Ying J, Fan Y, Zhong L, Liu X, Tsao SW, Chan AT, Tao Q. FEZF2, a novel 3p14 tumor suppressor gene, represses oncogene EZH2 and MDM2 expression and is frequently methylated in nasopharyngeal carcinoma. Carcinogenesis 2013; 34 (9): 1984–93.  Back to cited text no. 6
    
7.
Wang S, Cheng Y, Du W, Lu L, Zhou L, Wang H, Kang W, Li X, Tao Q, Sung JJ, Yu J. Zinc-finger protein 545 is a novel tumour suppressor that acts by inhibiting ribosomal RNA transcription in gastric cancer. Gut 2013; 62 (6): 833–41.  Back to cited text no. 7
    
8.
Yu J, Liang QY, Wang J, Cheng Y, Wang S, Poon TC, Go MY, Tao Q, Chang Z, Sung JJ. Zinc-finger protein 331, a novel putative tumor suppressor, suppresses growth and invasiveness of gastric cancer. Oncogene 2013; 32 (3): 307–17.  Back to cited text no. 8
    
9.
Fu L, Dong SS, Xie YW, Tai LS, Chen L, Kong KL, Man K, Xie D, Li Y, Cheng Y, Tao Q, Guan XY. Down-regulation of tyrosine aminotransferase at a frequently deleted region 16q22 contributes to the pathogenesis of hepatocellular carcinoma. Hepatology 2010; 51 (5): 1624–34.  Back to cited text no. 9
    
10.
Chen D, Dai C, Jiang Y. Histone H2A and H2B deubiquitinase in developmental disease and cancer. Cancer Transl Med 2015; 1 (5): 170.  Back to cited text no. 10
    
11.
Zhang Q, Zhang L, Li L, Wang Z, Ying J, Fan Y, Xu B, Wang L, Liu Q, Chen G, Tao Q, Jin J. Interferon regulatory factor 8 functions as a tumor suppressor in renal cell carcinoma and its promoter methylation is associated with patient poor prognosis. Cancer Lett 2014; 354 (2): 227–34.  Back to cited text no. 11
    
12.
Xu X, Wu J, Li S, Hu Z, Xu X, Zhu Y, Liang Z, Wang X, Lin Y, Mao Y, Chen H, Luo J, Liu B, Zheng X, Xie L. Downregulation of microRNA-182-5p contributes to renal cell carcinoma proliferation via activating the AKT/FOXO3a signaling pathway. Mol Cancer 2014; 13: 109.  Back to cited text no. 12
    
13.
Lin J, Deng Z, Tanikawa C, Shuin T, Miki T, Matsuda K, Nakamura Y. Downregulation of the tumor suppressor HSPB7, involved in the p53 pathway, in renal cell carcinoma by hypermethylation. Int J Oncol 2014; 44 (5): 1490–8.  Back to cited text no. 13
    
14.
Peters I, Gebauer K, Dubrowinskaja N, Atschekzei F, Kramer MW, Hennenlotter J, Tezval H, Abbas M, Scherer R, Merseburger AS, Stenzl A, Kuczyk MA, Serth J. GATA5 CpG island hypermethylation is an independent predictor for poor clinical outcome in renal cell carcinoma. Oncol Rep 2014; 31 (4): 1523–30.  Back to cited text no. 14
    
15.
Tatemoto K, Rökaeus A, Jörnvall H, McDonald TJ, Mutt V. Galanin – A novel biologically active peptide from porcine intestine. FEBS Lett 1983; 164 (1): 124–8.  Back to cited text no. 15
    
16.
Kordower JH, Le HK, Mufson EJ. Galanin immunoreactivity in the primate central nervous system. J Comp Neurol 1992; 319 (4): 479–500.  Back to cited text no. 16
    
17.
Berger A, Santic R, Hauser-Kronberger C, Schilling FH, Kogner P, Ratschek M, Gamper A, Jones N, Sperl W, Kofler B. Galanin and galanin receptors in human cancers. Neuropeptides 2005; 39 (3): 353–9.  Back to cited text no. 17
    
18.
Gundlach AL. Galanin/galp and galanin receptors: role in central control of feeding, body weight/obesity and reproduction? Eur J Pharmacol 2002; 440 (2-3): 255–68.  Back to cited text no. 18
    
19.
El-Salhy M, Starefeldt A. Direct effects of octreotide, galanin and serotonin on human colon cancer cells. Oncol Rep 2003; 10 (6): 1723–8.  Back to cited text no. 19
    
20.
El-Salhy M, Sitohy B. Triple therapy with octreotide, galanin and serotonin induces necrosis and increases apoptosis of a rat colon carcinoma. Regul Pept 2002; 108 (2-3): 55–62.  Back to cited text no. 20
    
21.
Misawa K, Kanazawa T, Misawa Y, Uehara T, Imai A, Takahashi G, Takebayashi S, Cole A, Carey TE, Mineta H. Galanin has tumor suppressor activity and is frequently inactivated by aberrant promoter methylation in head and neck cancer. Transl Oncol 2013; 6 (3): 338–46.  Back to cited text no. 21
    
22.
Misawa Y, Misawa K, Kanazawa T, Uehara T, Endo S, Mochizuki D, Yamatodani T, Carey TE, Mineta H. Tumor suppressor activity and inactivation of galanin receptor type 2 by aberrant promoter methylation in head and neck cancer. Cancer 2014; 120 (2): 205–13.  Back to cited text no. 22
    
23.
Perumal P, Vrontakis ME. Transgenic mice over-expressing galanin exhibit pituitary adenomas and increased secretion of galanin, prolactin and growth hormone. J Endocrinol 2003; 179 (2): 145–54.  Back to cited text no. 23
    
24.
Cheng Y, Liang P, Geng H, Wang Z, Li L, Cheng SH, Ying J, Su X, Ng KM, Ng MH, Mok TS, Chan AT, Tao Q. A novel 19q13 nucleolar zinc finger protein suppresses tumor cell growth through inhibiting ribosome biogenesis and inducing apoptosis but is frequently silenced in multiple carcinomas. Mol Cancer Res 2012; 10 (7): 925–36.  Back to cited text no. 24
    
25.
Bartfai T, Langel U, Bedecs K, Andell S, Land T, Gregersen S, Ahrén B, Girotti P, Consolo S, Corwin R, Crawley J, Xu XJ, Wiesenfeld-Hallin Z, Hökfelt T. Galanin-receptor ligand M40 peptide distinguishes between putative galanin-receptor subtypes. Proc Natl Acad Sci U S A 1993; 90 (23): 11287–91.  Back to cited text no. 25
    
26.
Gutkind JS. Cell growth control by G protein-coupled receptors: from signal transduction to signal integration. Oncogene 1998; 17 (11): 1331–42.  Back to cited text no. 26
    
27.
Jin Z, Olaru A, Yang J, Sato F, Cheng Y, Kan T, Mori Y, Mantzur C, Paun B, Hamilton JP, Ito T, Wang S, David S, Agarwal R, Beer DG, Abraham JM, Meltzer SJ. Hypermethylation of tachykinin-1 is a potential biomarker in human esophageal cancer. Clin Cancer Res 2007; 13 (21): 6293–300.  Back to cited text no. 27
    
28.
Misawa K, Kanazawa T, Misawa Y, Imai A, Uehara T, Mochizuki D, Endo S, Takahashi G, Mineta H. Frequent promoter hypermethylation of tachykinin-1 and tachykinin receptor type 1 is a potential biomarker for head and neck cancer. J Cancer Res Clin Oncol 2013; 139 (5): 879–89.  Back to cited text no. 28
    
29.
Mori Y, Cai K, Cheng Y, Wang S, Paun B, Hamilton JP, Jin Z, Sato F, Berki AT, Kan T, Ito T, Mantzur C, Abraham JM, Meltzer SJ. A genome-wide search identifies epigenetic silencing of somatostatin, tachykinin-1, and 5 other genes in colon cancer. Gastroenterology 2006; 131 (3): 797–808.  Back to cited text no. 29
    
30.
Wolfer A, Ramaswamy S. MYC and metastasis. Cancer Res 2011; 71 (6): 2034–7.  Back to cited text no. 30
    
31.
Dang CV. MYC on the path to cancer. Cell 2012; 149 (1): 22–35.  Back to cited text no. 31
    
32.
Li Z, Wang C, Prendergast GC, Pestell RG. Cyclin D1 functions in cell migration. Cell Cycle 2006; 5 (21): 2440–2.  Back to cited text no. 32
    
33.
Malumbres M, Barbacid M. Cell cycle, CDKs and cancer: a changing paradigm. Nat Rev Cancer 2009; 9 (3): 153–66.  Back to cited text no. 33
    
34.
Han K, Chen X, Bian N, Ma B, Yang T, Cai C, Fan Q, Zhou Y, Zhao TB. MicroRNA profiling identifies MiR-195 suppresses osteosarcoma cell metastasis by targeting CCND1. Oncotarget 2015; 6 (11): 8875–89.  Back to cited text no. 34
    
35.
Chu Q, Han N, Yuan X, Nie X, Wu H, Chen Y, Guo M, Yu S, Wu K. DACH1 inhibits cyclin D1 expression, cellular proliferation and tumor growth of renal cancer cells. J Hematol Oncol 2014; 7: 73.  Back to cited text no. 35
    
36.
Belguise K, Kersual N, Galtier F, Chalbos D. FRA-1 expression level regulates proliferation and invasiveness of breast cancer cells. Oncogene 2005; 24 (8): 1434–44.  Back to cited text no. 36
    
37.
Galvagni F, Orlandini M, Oliviero S. Role of the AP-1 transcription factor FOSL1 in endothelial cells adhesion and migration. Cell Adh Migr 2013; 7 (5): 408–11.  Back to cited text no. 37
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

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