Overexpression of inosine 5'-monophosphate dehydrogenase type II mediates chemoresistance to human osteosarcoma cells.
BACKGROUND
Chemoresistance is the principal reason for poor survival and disease recurrence in osteosarcoma patients. Inosine 5'-monophosphate dehydrogenase type II (IMPDH2) encodes the rate-limiting enzyme in the de novo guanine nucleotide biosynthesis and has been linked to cell growth, differentiation, and malignant transformation. In a previous study we identified IMPDH2 as an independent prognostic factor and observed frequent IMPDH2 overexpression in osteosarcoma patients with poor response to chemotherapy. The aim of this study was to provide evidence for direct involvement of IMPDH2 in the development of chemoresistance.


RESULTS
Stable cell lines overexpressing IMPDH2 and IMPDH2 knock-down cells were generated using the osteosarcoma cell line Saos-2 as parental cell line. Chemosensitivity, proliferation, and the expression of apoptosis-related proteins were analyzed by flow cytometry, WST-1-assay, and western blot analysis. Overexpression of IMPDH2 in Saos-2 cells induced strong chemoresistance against cisplatin and methotrexate. The observed chemoresistance was mediated at least in part by increased expression of the anti-apoptotic proteins Bcl-2, Mcl-1, and XIAP, reduced activation of caspase-9, and, consequently, reduced cleavage of the caspase substrate PARP. Pharmacological inhibition of IMPDH induced a moderate reduction of cell viability and a strong decrease of cell proliferation, but no increase in chemosensitivity. However, chemoresistant IMPDH2-overexpressing cells could be resensitized by RNA interference-mediated downregulation of IMPDH2.


CONCLUSIONS
IMPDH2 is directly involved in the development of chemoresistance in osteosarcoma cells, suggesting that targeting of IMPDH2 by RNAi or more effective pharmacological inhibitors in combination with chemotherapy might be a promising means of overcoming chemoresistance in osteosarcomas with high IMPDH2 expression.
Fellenberg
Jörg
J
Department of Experimental Orthopedics, Orthopedic University Hospital Heidelberg, Heidelberg, Germany. joerg.fellenberg@med.uni-heidelberg.de
Kunz
Pierre
P
Sähr
Heiner
H
Depeweg
Daniela
D
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D007168:IMP Dehydrogenase / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D020128:Inhibitory Concentration 50; D008727:Methotrexate / Q000494:pharmacology; D009173:Mycophenolic Acid / Q000494:pharmacology; D012516:Osteosarcoma / Q000235:genetics / Q000473:pathology*
D051017:Apoptosis Regulatory Proteins; D007168:IMP Dehydrogenase; C501687:IMPDH2 protein, human; D009173:Mycophenolic Acid; D002945:Cisplatin; D008727:Methotrexate
Int J Cancer. 2003 Jul 10;105(5):636-43
12740912
FEBS J. 2005 Feb;272(3):696-710
15670151
Int J Cancer. 2004 Mar 1;108(6):812-7
14712481
Proc Natl Acad Sci U S A. 1988 Sep;85(17):6533-7
2901100
J Clin Oncol. 1997 Jan;15(1):76-84
8996127
Life Sci. 2004 May 28;75(2):179-90
15120570
Br J Cancer. 1988 Jul;58(1):61-3
2901850
Cancer Res. 1991 Aug 1;51(15):3886-90
1677309
Adv Enzyme Regul. 1996;36:75-84
8869741
Ann N Y Acad Sci. 1993 Nov 30;696:88-93
7906497
Nature. 1975 Jul 24;256(5515):331-3
167289
Curr Opin Drug Discov Devel. 2007 Jul;10(4):403-12
17659481
Cancer Res. 1989 Jul 1;49(13):3696-701
2567208
Am J Clin Pathol. 1977 May;67(5):427-35
266360
Curr Opin Drug Discov Devel. 2006 Sep;9(5):595-605
17002220
Mol Cancer Ther. 2006 Feb;5(2):457-66
16505121
J Clin Oncol. 1991 Apr;9(4):600-5
2066757
Mod Pathol. 2007 Oct;20(10):1085-94
17660802
Curr Med Chem. 1999 Jul;6(7):561-74
10390601
Anticancer Res. 2000 Jul-Aug;20(4):2329-38
10953293
J Clin Oncol. 2005 Jan 20;23(3):559-68
15659502
Farmaco. 1996 Jul;51(7):457-69
8765668
J Clin Oncol. 1992 Jan;10(1):5-15
1370176
Cancer Res. 1992 Jan 15;52(2):258-61
1345808
J Biol Chem. 2008 May 2;283(18):12387-92
18305114
Cancer Res. 1989 Feb 15;49(4):996-1000
2643467
Oncogene. 2005 Sep 1;24(38):5888-96
15940263
Genes Dev. 1996 Apr 15;10(8):934-47
8608941
Med Sci Monit. 2005 Jan;11(1):BR6-12
15614187
Blood. 1987 Feb;69(2):634-9
2879579
Leukemia. 1994 Aug;8(8):1257-63
7520100
Anticancer Res. 1996 Nov-Dec;16(6A):3349-51
9042310