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Molecular Oncology, Markers, Clinical Correlates |
1 Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania; 2 Department of Surgery, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania; and 3 Istituto Dermopatico dellImmacolata, Rome, Italy
| ABSTRACT |
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Experimental Design: We examined 20 paired normal and non-small cell lung cancer samples for the presence of Parkin alterations in the coding sequence and changes in gene expression. We also restored gene expression in the Parkin-deficient lung carcinoma cell line H460 by use of a recombinant lentivirus containing the wild-type Parkin cDNA.
Results: Loss of heterozygosity analysis identified a common region of loss in the Parkin/FRA6E locus with the highest frequency for the intragenic marker D6S1599 (45%), and semi-quantitative reverse transcription-PCR revealed reduced expression in 3 of 9 (33%) lung tumors. Although we did not observe any in vitro changes in cell proliferation or cell cycle, ectopic Parkin expression had the ability to reduce in vivo tumorigenicity in nude mice.
Conclusion: These data suggest that Parkin is a tumor suppressor gene whose inactivation may play an important role in non-small cell lung cancer tumorigenesis.
| INTRODUCTION |
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Recently, Parkin, a gene implicated in autosomal recessive juvenile Parkinsonism (10) , was found to be a target of LOH (4) at chromosome 6q25-q27 in breast and ovarian carcinomas (11 , 12) . Although various deletions and point mutations have been described in patients with early onset of Parkinsonism (13) , mutation analysis failed to identify somatic point mutations in any of the breast or ovarian tumors with LOH at the Parkin/FRA6E locus examined (11) . However, truncating deletions were found in 3 of 20 tumor samples, and homozygous deletions of exon 2 were identified in the lung adenocarcinoma cell lines Calu-3 and H-1573 (11) . In addition, Parkin expression was down-regulated or absent in the majority of the breast and ovarian samples examined, suggesting that Parkin expression is targeted by the LOH observed at 6q25-q27 and may play a role in the development of these tumors.
In this report, we describe the LOH analysis of the Parkin/FRA6E locus at 6q25-q27 and the status of the Parkin coding sequence and its expression in 20 matched normal and non-small cell lung cancer (NSCLC) samples in gene sequence screening. The identification of a common region of deletion in combination with the absence of or down-regulated expression in these tumors indicates that Parkin is targeted by LOH in lung tumorigenesis. In addition, we show the in vivo reduction of tumorigenicity in the lung-tumor-derived cell line H460 lentivirally transduced with recombinant Parkin. Overall, these data suggest that Parkin is a TSG that may play an important role in the development of lung cancer.
| MATERIALS AND METHODS |
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LOH Analysis.
LOH analysis was performed by a PCR approach using fluorescently end-labeled primers derived from the chromosome 6q25-q27 region as described previously (11)
. Primer sequences for each highly polymorphic (>60%) microsatellite markers used (Table 1)
are available at the National Center for Biotechnology Information database.3
PCR and fragment analysis were performed as described previously (11)
. LOH was defined for those samples that had XLOH values <0.7 or an allelic loss of
40%.
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Mutation Analysis.
Mutation analysis was performed as described previously (14)
. PCR products were resolved on Tris-borate-EDTA 2% agarose gels and purified by use of the Qiagen Gel Extraction kit (Qiagen, Valencia, CA) followed by direct sequencing. The following primer pairs were used: ParkFw (5'-CCAGTGACCATGATAGTGTT-3')/ParkRw (5'-TGAAGGTAGACACTGGGTAT-3'); and ParkIIFw (5'-CAGAGACCGTGGAGAAAAGG-3')/ParkIIRw (5'-CTGCTGGTACCGGTTGTACT-3'). In addition, six sets of oligonucleotide primers were designed to amplify Parkin exons from genomic DNA isolated from patients undergoing cancer surgery by standard methods (15)
. PCR conditions and primer sequences are available on request. All sequence analyses and alignments were performed with the SEQUENCER program (Gene Codes, Ann Arbor, MI).
Methylation-Specific PCR.
The methylation status of the Parkin promoter (16)
was analyzed by amplification of a 541-bp PCR product including the first exon (followed by bisulfite sequencing as described; Ref. 17
) in all samples used for RT-PCR. Primer sequences and conditions are available on request.
Lentiviral Vector Production and in Vitro Transduction.
The full-length Parkin cDNA in frame with a carboxyl-terminal hemagglutinin epitope tag was generated by PCR and cloned into the BamHI site of the pNaldini.CMV.IRES.EGFP self-inactivating HIV-based provirus vector. Primers are available on request. Lentiviral vector production by transient transfection was performed as described previously (18, 19, 20)
. Transient transfections of pNaldini.CMV.IRES.EGFP or pNaldini.CMV.PARKINHA.IRES.EGFP and packaging vectors into 293FT cells (Invitrogen) were performed by the calcium phosphate precipitation method using the ProFection Mammalian Transfection System (Promega, Madison, WI) according to the manufacturers instructions. Viruses were pseudotyped with the vesicular stomatitis virus glycoprotein (VSVG) with use of the pVSV-G vector (Clontech, Palo Alto, CA). Viral supernatants were collected after 48 and 72 h, filtered, and snap-frozen in liquid nitrogen. Titers were determined by infecting 293FT cells with serial dilutions of virus supplemented with Polybrene (Sigma, St. Louis, MO) at a final concentration of 8.0 µg/ml. Infectivity was determined by green fluorescent protein (GFP) expression analysis of target cells by flow cytometry (FACSCalibur; Becton Dickinson Immunocytometery Systems) 48 h after infection. Transduction units are expressed as a percentage of GFP-positive cells relative to the total number of cells analyzed. Typically, conditioned medium collected from transfections performed in T-175 flasks (Becton Dickinson) seeded with 5 x 106 293FT cells yielded
110 x 107 transduction units/ml. Subsequently, infections of target cells were performed to achieve 90100% GFP-positive cells.
Cell Cycle and Cell Proliferation Analysis.
For cell cycle analysis, cells were harvested 24 and 48 h post-transduction, washed in PBS, and fixed in ethanol. After RNase treatment (Roche, Indianapolis, IN), cells were stained with 50 µg/ml propidium iodide (Molecular Probes). All samples were analyzed by flow cytometry (FACSCalibur) and the FlowJo Version 3.4 Software Package (Tree Star, Inc., San Carlos, CA). Cell proliferation was measured by the Cell Titer 96 Aqueous One Solution Cell Proliferation Assay (MTS) according to the manufacturers directions (Promega).
Tumorigenicity in Nude Mice.
Cells transduced with and without Parkin cDNA were evaluated for tumorigenicity in nude mice. We gave 6-week-old female athymic mice nude (nu/nu) s.c. injections containing 110 x 106 cells in 0.2 ml of PBS. Cells transduced with each construct were injected into three to four mice each and followed individually. Mice were examined two to three times per week for tumor formation at the sites of injection for 5 weeks. Tumors were measured with linear calipers, and tumor volumes were calculated (v = ab2/2).
| RESULTS AND DISCUSSIONS |
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3 Mb. The percentage of LOH for each of the five markers ranged from 9% (D6S1579) to 45% (D6S1599). The intragenic marker D6S1599 is located in the 5' end of the Parkin gene, between exons 2 and 3, and the minimal region of LOH is delineated by the markers D6S305 and D6S1599 (Fig. 1
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To study the in vitro and in vivo effects of restored Parkin gene expression, we used a self-inactivating lentiviral system of gene transfer to infect the human tumor-derived cell line H460, which lacks endogenous Parkin expression (11)
. Infection efficiencies >90% were observed in H460 cells by recombinant lenti-viruses containing Parkin or EGFP alone. Typically, Parkin and EGFP gene expression levels became stable 48 h postinfection and continued for several weeks (>12 weeks). In each of these infections, there were no cytotoxic effects or changes in growth characteristics and cell cycle in H460 cells (Fig. 3)
. These data suggest that in vitro there are no direct consequences of ectopic Parkin expression on cell growth or cell cycle in these cells.
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34-fold relative to the controls. Thus, Parkin alone has significant tumor-suppressor activity in H460 cells deficient in the Parkin protein (11)
. Homozygous deletions of exon 2 of Parkin, a gene implicated in autosomal recessive juvenile Parkinsonism (10) , were identified in the lung adenocarcinoma cell lines Calu-3 and H-1573 (11) . In addition, Western analysis of several lung cell lines positive for Parkin RNA expression failed to detect any Parkin protein, thus prompting our investigation of the possible role of Parkin in NSCLC. Although various deletions and point mutations have been described in patients with early onset of Parkinsonism (13) , mutation analysis failed to identify somatic point mutations in any of the lung tumors examined for LOH at the Parkin/FRA6E locus (11) . Parkin expression was down-regulated or absent in a significant portion of the lung samples examined, suggesting that Parkin expression is targeted by the LOH observed at 6q25-q27 and may play a role in the development of these tumors. In vivo studies showed that re-expression of Parkin in a lung carcinoma cell line, although having no direct consequences on cell growth or cell cycle, consistently reduced the volumes of tumors in nude mice. Although its function is not entirely understood, Parkin protein was found to be an ubiquitin-protein ligase (E3). It is therefore possible that mechanisms related to the ubiquitin function are involved in the tumorigenic process. Of note, the FHIT gene, a TSG located in FRA3B, was found to be deleted/down-regulated but not mutated in lung cancer (22) , and WWOX, another TSG located in a fragile site (FRA16D), is deleted/truncated in several types of cancers, including NSCLC (23) .
In summary, we have expanded the histological spectrum of tumors in which the candidate TSG Parkin is genetically altered to include NSCLCs. In addition, using a lentiviral system, we demonstrated that in vivo effects of restored Parkin gene expression are compatible with a tumor suppressor function. These data argue that Parkin is a TSG whose inactivation may play an important role in NSCLC tumorigenesis.
| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Note: M. C. Picchio, E. S. Martin, and R. Cesari contributed equally to the study.
Requests for reprints: Carlo Maria Croce, Kimmel Cancer Center, 233 South 10th Street, BLSB 1050, Philadelphia, PA 19107. Phone: (215) 503-4645; Fax: (215) 923-3528; E-mail: croce{at}calvin.jci.tju.edu
3 http://www.ncbi.nlm.nih.gov/. ![]()
Received 8/25/03; revised 11/11/03; accepted 11/18/03.
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