Aberrant Expression of Proptprn2 in Cancer Cells Confers Resistance to Apoptosis Alexey V
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Published OnlineFirst April 15, 2015; DOI: 10.1158/0008-5472.CAN-14-2718 Cancer Molecular and Cellular Pathobiology Research Aberrant Expression of proPTPRN2 in Cancer Cells Confers Resistance to Apoptosis Alexey V. Sorokin1, Binoj C. Nair1,Yongkun Wei2, Kathryn E. Aziz1, Valentina Evdokimova3, Mien-Chie Hung2,4, and Junjie Chen1 Abstract The protein tyrosine phosphatase receptor PTPRN2 is whereas enforced expression of proPTPRN2 in nontransformed expressed predominantly in endocrine and neuronal cells, human mammary epithelial cells exerted a converse effect. where it functions in exocytosis. We found that its immature Mechanistic investigations suggested that ProPTPRN2 elicited isoform proPTPRN2 is overexpressed in various cancers, includ- these effects through direct interaction with TRAF2, a hub ing breast cancer. High proPTPRN2 expression was associated scaffold protein for multiple kinase cascades, including ones strongly with lymph node–positive breast cancer and poor that activate NF-kB. Overall, our results suggest PTPRN2 as a clinical outcome. Loss of proPTPRN2 in breast cancer cells novel candidate biomarker and therapeutic target in breast promoted apoptosis and blocked tumor formation in mice, cancer. Cancer Res; 75(9); 1–13. Ó2015 AACR. Introduction in nervous system and pancreatic endocrine cells, where it exists as a mature isoform and participates in exocytosis of insulin-con- Reversible protein tyrosine phosphorylation is an integral part taining secretory granules (5). While lacking protein phosphatase of cellular signaling that controls many if not all aspects of cell activity due to two critical amino acid substitutions in its PTP biology and development. Net protein tyrosine phosphorylation domain (6), PTPRN2 possesses weak phosphatidylinositol phos- is governed by the dynamic equilibrium between two counter- phatase (PIP) activity (7). By analyzing tissue microarrays (TMA), acting enzyme families, namely protein tyrosine kinases and we found that the expression of the immature isoform, protein tyrosine phosphatases (PTP). Because tyrosine kinases proPTPRN2, was strongly associated with lymph node–positive were mostly described as oncogenes, PTPs were initially postu- breast cancer and poor clinical outcome. Furthermore, we estab- lated to function as tumor suppressors. However, among 37 PTPs lished that it is the immature proPTPRN2 but not the mature implicated in human cancer (1, 2), approximately equal propor- isoform that is capable of disrupting normal mammary morpho- tions have been ascribed with oncogenic and tumor suppressor genesis and promoting tumor growth in mouse xenografts and activities (3). In addition to protein substrates, some PTPs were breast cancer cell lines. Mechanistically, proPTPRN2 appears to shown to dephosphorylate mRNAs, inositol phospholipids, or to mediate this effect through the interaction with the TNF receptor be catalytically inactive while remaining functional (4). The (TNFR)–associated factor 2 (TRAF2), by suppressing apoptosis in precise impact of these and other individual PTPs on tumorigen- a TRAF2-dependent manner. Given that proPTPRN2 is expressed esis remain unclear. exclusively in cancer cells, our data provide a novel diagnostic tool To find novel cancer-associated PTPs, we interrogated publicly and a unique targeting opportunity for treatment of aggressive available databases and identified a tyrosine phosphatase–like lymph node–positive breast cancer. protein PTPRN2 as being significantly overexpressed in a subset of tumors, including colon, prostate, pancreas, and breast cancers. PTPRN2, also known as phogrin, IA-2b, ICAAR, and NE-6, Materials and Methods belongs to the PTP receptor type N family. It is normally expressed Antibodies Cleaved caspase-3, JNK1, phospho JNK1 (Thr183/Tyr185), IKKa, phospho IKKa/b (Ser176/180), IKKe, phospho IKKe 1Department of Experimental Radiation Oncology, The University of (Ser172), IkB, NFkB, PKC phospho substrate, Akt, phospho Akt 2 Texas MD Anderson Cancer Center, Houston, Texas. Department of (Ser473), PKCa,PKCz, phospho PKC pan (bII Ser660), TNFR1, Molecular and Cellular Oncology,The University of Texas MDAnderson Cancer Center, Houston, Texas. 3Department of Genomics, Ontario TNFR2, Fas, DR3, DR5, TRAF2, TRADD, FADD, and mouse Institute for Cancer Research, Toronto, Ontario, Canada. 4Center for anti-rabbit IgG (conformation specific) antibodies were obtained Molecular Medicine and Graduate Institute of Cancer Biology, China from Cell Signaling Technology. PTPRN2 (HPA026656, Medical University, Taichung, Taiwan. SAB4502542, and HPA006900), FLAG(M2), HA, b-actin, PARP1 Note: Supplementary data for this article are available at Cancer Research monoclonal (C-2-10), and a-tubulin monoclonal antibodies were Online (http://cancerres.aacrjournals.org/). obtained from Sigma. Ki-67 antibody was obtained from Corresponding Author: Junjie Chen, The University of Texas MD Anderson Abcam. c-Myc antibody was obtained from Santa Cruz Biotechnol- Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030. Phone: 713-792-4863; ogy. m-Calpain antibody was obtained from EMD Millipore. Sin- Fax: 713-794-5369; E-mail: [email protected] taxin 6, calnexin, and E-cadherin antibodies were obtained fromBD doi: 10.1158/0008-5472.CAN-14-2718 Biosciences. Phospho TRAF2 (Ser11) antibody was kindly provided Ó2015 American Association for Cancer Research. by Dr. Hasem Habelhah at the University of Iowa (Iowa City, IA). www.aacrjournals.org OF1 Downloaded from cancerres.aacrjournals.org on September 27, 2021. © 2015 American Association for Cancer Research. Published OnlineFirst April 15, 2015; DOI: 10.1158/0008-5472.CAN-14-2718 Sorokin et al. Plasmids doxycycline) and layered onto 2 mL of 0.5% agar beds in 6-well All constructs were generated by PCR and subcloned into plates. Cells were fed with 1 mL of medium every 3 days for 30 pDONR201 vector using Gateway Technology (Invitrogen). The days, and colonies were then examined by phase-contrast micros- entry clones with corresponding cDNAs were transferred into copy and photographed. Colonies larger than 30 mm in diameter Gateway-compatible destination vectors with an N-terminal were considered positive. Myc epitope or a C-terminal SFB tag, or into a doxycycline- inducible vector with a C-terminal SFB tag. All constructs were Western blot analysis and immunofluorescence microscopy fi veri ed by sequencing. GFP-FLuc-Lentiviral vector was described Western blot analysis was performed as described previously previously (8). (13, 14). For immunofluorescence microscopy, cells cultured on coverslips were washed with phosphate-buffered saline, fixed Tandem affinity purification of SFB-tagged protein complexes with 3% paraformaldehyde for 20 minutes, and permeabilized HEK293T cells were transfected with plasmids encoding SFB- with 0.5% (v/v) Triton X-100 solution for 5 minutes. Coverslips tagged proteins. Cell lines stably expressing the tagged protein were washed with PBS and immunostained with primary anti- were selected by culturing in medium containing puromycin (2 bodies in 5% goat serum for 60 minutes. Cells were then washed mg/mL) and confirmed by immunofluorescence staining and and incubated with rhodamine- or FITC-conjugated secondary Western blot analysis. Tandem affinity purification was per- antibodies for 60 minutes, and nuclei were stained with 1 mg/mL formed as described previously (9). The eluted proteins were 40,6-diamidino-2-phenylindole (DAPI). Slides were mounted identified by mass spectrometry analysis, which was performed and visualized using a Nikon ECLIPSE E800 fluorescence micro- by the Taplin Biological Mass Spectrometry Facility (Harvard scope with a Nikon Plan Fluor 10Â objective lens at room Medical School, Boston, MA). temperature. Cells were photographed using a SPOT camera (Diagnostic Instruments) and analyzed using Photoshop soft- Cell culture and transfection ware (Adobe). HEK293T, HeLa, MCF7, MCF10A, SKBR3, MDA-MB-231, MDA-MB-468, MDA-MB-435, MDA-MD-436, MDA-MB-453, Tumor xenograft studies and bioluminescence imaging T47D, BT474, AU565, A498, ACHN, 769-P, 486-O, VCap, PC3, All animal experiments were performed in accordance with a BPH1, DU145, RKO, HCT116, HCT15, 639V, 647V, HT1197, protocol approved by the Institutional Animal Care and Use HT1376, RT4, and T24 cells were purchased from ATCC and Committee of The University of Texas MD Anderson Cancer fi cultured under conditions speci ed by the manufacturer. Center (Houston, TX). For xenograft tumor assays, 5 Â 106 tumor MCF10A cells were maintained as described previously (10). cells were resuspended in 100 mL of Matrigel diluted with PBS at Cells were tested for mycoplasma contamination. Cell transfec- 1:1 ratio and injected subcutaneously into flanks of anesthetized tion was performed using Lipofectamine 2000 or polyethylenei- 6- to 8-week-old female BALB/c mice. Orthotopic tumors were mine, according to the manufacturer's protocols. developed by injecting 1 Â 106 cells in 100 mL of PBS into mammary fat pads. Mice were sacrificed when they met the Flow cytometry, cell growth, and viability assays institutional criteria for tumor size and overall health condition. To determine growth rates, equal numbers of cells were plated The tumors were removed and measured. For bioluminescence onto 6 cm dishes. Beginning the next day, cells were trypsinized imaging, 150 mg/kg body weight D-luciferin (Firefly, potassium and counted daily. To determine cell viability, cells were trypsi- salt, PerkinElmer) was injected intraperitoneally 15 minutes nized