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Advances in Brief |
B p65 Mediates Tumor Necrosis Factor
-induced Nuclear Translocation of Telomerase Reverse Transcriptase Protein1
Jerome Lipper Multiple Myeloma Center, Department of Medical Oncology, Dana-Farber Cancer Institute, and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115 [M. A., T. Hi., T. Ha., Y-T. T., C. S. M., N. M., D. C., P. R., N. C. M., K. C. A.], and Veterans Administration Boston Healthcare System, West Roxbury, Massachusetts 02132 [N. C. M.]
| ABSTRACT |
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B p65 in MM.1S cells. Importantly, tumor necrosis factor
(TNF
) modulates telomerase activity by inducing translocation from the cytoplasm to the nucleus of hTERT protein bound to NF-
B p65. Conversely, a specific I
B kinase (IKK) inhibitor PS-1145, and a specific NF-
B nuclear translocation inhibitor SN-50, both block TNF
-induced hTERT nuclear translocation. These studies suggest that NF-
B p65 plays a pivotal role in regulating telomerase by modulating its nuclear translocation. | Introduction |
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B (4)
. Moreover, phosphorylation (5, 6, 7)
and the nuclear translocation (6)
of hTERT are additional mechanisms regulating telomerase activity. Specifically, up-regulation of telomerase activity in human T lymphocytes is associated with the phosphorylation of hTERT protein and its nuclear translocation (6)
. Recently, it has been reported that hTERT protein located in the nucleolus is modulated to nucleoplasm by oncoproteins, as well as by cell cycle and by DNA damage (8, 9, 10)
. To date, however, the mechanism regulating cytoplasmic to nuclear translocation of hTERT protein is undefined.
Our previous studies have shown that TNF
activates NF-
B (11)
, and that telomerase is a downstream target of NF-
B (7)
. Given the requirement for nuclear translocation of activated NF-
B to modulate gene transcription (12)
and its known role in nuclear translocation of tumor suppressor proteins p53 (13)
and menin (14)
, we in this study determined whether NF-
B p65 mediated nuclear translocation of hTERT in human MM cells. We demonstrate that hTERT protein interacts directly with NF-
B p65 in MM.1S cells, and that TNF
modulates telomerase activity by inducing nuclear translocation of hTERT protein bound to NF-
B p65. Conversely, a specific IKK inhibitor PS-1145 (15)
and a specific NF-
B nuclear translocation inhibitor SN-50 (16)
, both block TNF
-induced hTERT nuclear translocation. These studies suggest that NF-
B p65 plays a pivotal role in regulating telomerase activity by modulating its nuclear translocation.
| Materials and Methods |
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(R&D Systems, Minneapolis, MN) was reconstituted with sterile PBS and stored at -20°. Activated recombinant Akt was purchased from Upstate Biotechnology (Lake Placid, NY). IKK inhibitor PS-1145 was obtained from Millennium Pharmaceuticals (Cambridge, MA), and NF-
B nuclear translocation inhibitor SN-50 was obtained from BIOMOL (Plymouth Meeting, PA).
Cell Line and Cell Culture.
Human MM cell line MM.1S was kindly provided by Dr. Steven Rosen (Northwestern University, Chicago, IL). MM.1S cells were cultured in RPMI 1640 (Mediatech, Herndon, VA) with 10% fetal bovine serum (Harlan, Indianapolis, IN) containing 2 mM L-glutamine, 100 units/ml penicillin, and 100 µg/ml streptomycin (Life Technologies, Inc., Grand Island, NY). Before experimental treatments, MM.1S cells were grown in serum-free media for 24 h.
Telomerase Assay.
The telomerase assay was performed using a TRAPEZE Telomerase Detection kit (Oncor, Gaithersburg, MD). Extracts of whole cells, as well as cytoplasmic and nuclear fractions, were prepared using Nuclear Extract kit (Active Motif, Carlsbad, CA). After incubation with the extracts (50 ng) for 20 min at 30°, PCR amplification was performed with 30 cycles at 94° for 30 s, at 58° for 30 s, and at 72° for 60 s. The PCR products were analyzed by electrophoresis on 12% polyacrylamide nondenaturing gels and stained with SYBR Green I (Molecular Probes, Eugene, OR). Telomerase activity was assessed by determining the ratio of the entire telomerase ladder to that of the internal control, using NIH image analysis software.
Immunoblotting.
Cells were harvested, washed with ice-cold PBS, and lysed with buffer containing 50 mM Tris-HCl (pH 7.4), 150 mM NaCl, 1% NP40, 2 mM sodium orthovanadate, and protease inhibitor cocktail (Roche Diagnostics Corp., Indianapolis, IN). An equal amount (100 µg) of the samples was separated on SDS-polyacrylamide gel and then transferred onto nitrocellulose filters (Bio-Rad, Hercules, CA). The membranes were immunoblotted with Abs against hTERT (Calbiochem, La Jolla, CA), NF-
B p65 (Santa Cruz Biotechnology, Santa Cruz, CA), nucleolin (Santa Cruz Biotechnology), and
-tubulin (Sigma Chemical, St. Louis, MO). The immunoblots were detected by ECL chemiluminescence (Pharmacia, Uppsala, Sweden).
Immunoprecipitation.
Cells lysates were incubated with anti-hTERT Ab (Calbiochem) or anti-NF-
B p65 Ab (Santa Cruz Biotechnology) overnight, and then immunoprecipitated for 4 h with protein A-Sepharose (CL-4B; Pharmacia). Immune complexes were washed, electrophoresed, and analyzed by immunoblotting with Abs against hTERT or NF-
B p65.
We also analyzed the binding of NF-
B p65 to phosphorylated versus unphosphorylated hTERT proteins. Immunoprecipitates of hTERT in cell lysates were incubated with or without activated recombinant Akt (Upstate Biotechnology) in protein kinase reaction buffer [20 mM HEPES (pH 7.4), 10 mM MgCl2, 1 mM DTT, 1 mM ATP, and 1.3 mM CaCl2] at 30° for 30 min. The reactions were stopped by heating to 95° for 10 min. Phosphorylated and unphosphorylated hTERT proteins were incubated with NF-
B p65 immunoprecipitates obtained by incubating with NF-
B TransCruz Oligonucleotide Agarose Conjugates (Santa Cruz Biotechnology) for 4 h, washed, electrophoresed, and analyzed by immunoblotting with Abs against hTERT, phospho-NF-
B p65 (Cell Signaling, Beverly, MA), and NF-
B p65.
We next analyzed the binding of hTERT to phosphorylated versus unphosphorylated NF-
B p65. MM.1S cells were cultured with TNF
(10 ng/ml) in the presence or absence of PS-1145 (10 µM) for 1 h. MM.1S cell lysates were then immunoprecipitated with Sepharose conjugated to anti-hTERT Ab for 4 h. Immune complexes were washed, electrophoresed, and analyzed by immunoblotting with Abs against hTERT, phospho-NF-
B p65, and NF-
B p65.
Cytoplasmic and Nuclear Fractionation.
The preparation of cytoplasmic and nuclear extracts was performed using the Nuclear Extract kit (Active Motif) according to manufacturers instructions. Supernatants were harvested as cytoplasmic fractions. Pellets were resuspended in 50 µl of Complete Lysis Buffer and centrifuged at 14,000 x g for 10 min at 4°; supernatants were saved as the nuclear fractions.
| Results and Discussion |
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B regulates telomerase activity in MM cells (7)
. The requirement for nuclear localization of hTERT protein to elongate telomere sequences, coupled with the role of nuclear translocation of NF-
B to either modulate gene transcription (12)
, or to transport tumor suppressor proteins (13
, 14)
, provided the rationale for our investigation to define whether NF-
B mediates translocation of hTERT protein from the cytoplasm to the nucleus in MM cells. We found that constitutive association of hTERT protein with NF-
B p65 protein is transiently up-regulated by TNF
in MM.1S cells (Fig. 1A and C)
B p65 (Fig. 1D)
|
-induced NF-
B p65 and hTERT protein expression in cytoplasmic and nuclear fractions. As shown in Fig. 2A
triggers a decrease of NF-
B p65 protein in cytoplasm (0 h, 78.3%; 0.5 h, 47.8%; 1 h, 41.1%), with a corresponding increase in the nucleus (0 h, 21.7%; 0.5 h, 52.2%; 1 h, 58.9%). A specific IKK inhibitor PS-1145 blocked TNF
-induced NF-
B p65 translocation (cytoplasm: 0 h, 78.3%; 0.5 h, 56.1%; 1 h, 69.0%; nucleus: 0 h, 21.7%; 0.5 h, 43.9%; 1 h, 31.0%), as did a specific NF-
B nuclear translocation inhibitor SN-50 (cytoplasm: 0 h, 78.3%; 0.5 h, 64.9%; 1 h, 67.7%; nucleus: 0 h, 21.7%; 0.5 h, 35.1%; 1 h, 32.3%). Importantly, TNF
also induced translocation of hTERT protein from the cytoplasm (0 h, 96.2%; 0.5 h, 71.2%; 1 h, 63.3%) to the nucleus (0 h, 3.8%; 0.5 h, 28.8%; 1 h, 36.7%), which was also inhibited by PS-1145 (cytoplasm: 0 h, 97.8%; 0.5 h, 98.3%; 1 h, 98.6%; nucleus: 0 h, 2.2%; 0.5 h, 1.7%; 1 h, 1.4%) and by SN-50 (cytoplasm: 0 h, 97.8%; 0.5 h, 98.2%; 1 h, 97.5%; nucleus: 0 h, 2.2%; 0.5 h, 1.8%; 1 h, 2.5%; Fig. 2B
-treatment; moreover, PS-1145 and SN-50 inhibited TNF
-induced nuclear translocation of hTERT protein.
|
induces nuclear translocation of hTERT protein-NF-
B p65 complexes. TNF
induced the nuclear translocation of hTERT protein-NF-
B p65 complexes; PS-1145 inhibited the translocation (Fig. 3, A and B)
-treatment; moreover, PS-1145 inhibited TNF
-induced nuclear translocation of hTERT protein (Fig. 3C)
B p65 showed that TNF
induced nuclear translocation of NF-
B p65 and that PS-1145 inhibited this process (Fig. 3D)
-induced nuclear translocation of hTERT-NF-
B p65 complexes (Fig. 3, E and F)
|
B p65, which was obtained using agarose beads conjugated to NF-
B binding sequences. hTERT protein, phosphorylated in vitro by recombinant Akt kinase, binds phosphorylated NF-
B p65 (Fig. 3G)
B p65, hTERT protein was separated from whole MM.1S cell lysate using Sepharose conjugates to anti-hTERT Ab. TNF
induced phosphorylation of NF-
B p65, which bound hTERT protein; conversely, PS-1145 blocked TNF
-induced binding of hTERT protein to phosphorylated NF-
B p65 (Fig. 3H)
B p65 mediates the nuclear translocation of phosphorylated hTERT protein.
We next evaluated telomerase activity in TNF
-treated MM.1S cells. We detected no significant change in telomerase activity in whole cell fractions of treated cells versus control cells: control MM.1S cells (1.00 ± 0.00), PS-1145-treated MM.1S cells (0.92 ± 0.05), SN-50-treated MM.1S cells (0.95 ± 0.07), TNF
-treated MM.1S cells (1.10 ± 0.05), TNF
and PS-1145-treated MM.1S cells (1.00 ± 0.10), and TNF
and SN-50-treated MM.1S cells (1.00 ± 0.10; Fig. 4
). Telomerase activity in untreated control cells was higher in cytoplasmic than in nuclear fractions, and both PS-1145 and SN-50 inhibited telomerase activity in nuclear fraction: 66.3 ± 3.7%, 78.9 ± 1.5%, and 89.8 ± 1.0% in cytoplasm versus 33.6 ± 3.7%, 21.1 ± 1.5%, and 10.2 ± 1.0% in the nucleus of control, PS-1145-treated, and SN-50-treated MM.1S cells, respectively (Fig. 4)
. Importantly, TNF
induced telomerase activity in the nuclear fraction (79.5 ± 2.5%), which was blocked by both PS-1145 (41.1 ± 3.0%) and SN-50 (31.5 ± 4.2%; Fig. 4
). These results suggest that nuclear translocation of hTERT protein and telomerase activity is regulated by phosphorylated NF-
B p65.
|
B activation confers resistance to apoptosis and conventional chemotherapy (15
, 17
, 18)
. We recently demonstrated that TNF
in the BM microenvironment induces NF-
B-dependent alterations in adhesion molecule expression on both MM cells and BM stromal cells, with resulting increased cell adhesion, enhanced tumor cell growth, and cell-adhesion-mediated drug resistance (11)
. Excitingly, drugs that abrogate NF-
B activation in both MM cells and BM microenvironment, including immunomodulatory derivatives of thalidomide (IMiDs) and the proteasome inhibitor PS-341, can overcome drug resistance in preclinical and early clinical studies, and, therefore, have great potential to improve patient outcome (15
, 16
, 19)
. Activation of telomerase plays an important role in the evolution from monoclonal gammopathy of undetermined significance to MM (20)
, and MM patients with high levels of telomerase activity have poor prognosis (21)
. The present study confirms that NF-
B plays a pivotal role in regulating telomerase via nuclear translocation of hTERT protein, further supporting the potential utility of novel therapeutics targeting NF-
B in MM.
| FOOTNOTES |
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1 Supported by NIH Grants RO-1 50947 and PO-1 78378, the Multiple Myeloma Research Foundation (to T. Hi., T. Ha., D. C.), Veterans Affairs Merit Review and Leukemia and Lymphoma Society Scholar in translational research award (to N. C. M.), the Cure Myeloma Fund, the Myeloma Research Fund, and the Doris Duke Distinguished Clinical Research Scientist Award (to K. C. A.). ![]()
2 To whom requests for reprints should be addressed, at Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115. Phone: (617) 632-2144; Fax: (617) 632-2140; E-mail: kenneth_anderson{at}dfci.harvard.edu ![]()
3 The abbreviations used are: hTERT, human telomerase reverse transcriptase; MM, multiple myeloma; NF-
B, nuclear factor
B; TNF
, tumor necrosis factor
; Ab, antibody; BM, bone marrow; IKK, I
B kinase. ![]()
Received 9/16/02. Accepted 11/ 8/02.
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