Osteopontin selectively regulates p70S6K/mTOR phosphorylation leading to NF-kappaB dependent AP-1-mediated ICAM-1 expression in breast cancer cells.
BACKGROUND
Breast cancer is one of the most frequently diagnosed cancer and accounts for over 400,000 deaths each year worldwide. It causes premature death in women, despite progress in early detection, treatment, and advances in understanding the molecular basis of the disease. Therefore, it is important to understand the in depth mechanism of tumor progression and develop new strategies for the treatment of breast cancer. Thus, this study is aimed at gaining an insight into the molecular mechanism by which osteopontin (OPN), a member of SIBLING (Small Integrin Binding LIgand N-linked Glycoprotein) family of protein regulates tumor progression through activation of various transcription factors and expression of their downstream effector gene(s) in breast cancer.


RESULTS
In this study, we report that purified native OPN induces ICAM-1 expression in breast cancer cells. The data revealed that OPN induces NF-kappaB activation and NF-kappaB dependent ICAM-1 expression. We also observed that OPN-induced NF-kappaB further controls AP-1 transactivation, suggesting that there is cross talk between NF-kappaB and AP-1 which is unidirectional towards AP-1 that in turn regulates ICAM-1 expression in these cells. We also delineated the role of mTOR and p70S6 kinase in OPN-induced ICAM-1 expression. The study suggests that inhibition of mTOR by rapamycin augments whereas overexpression of mTOR/p70S6 kinase inhibits OPN-induced ICAM-1 expression. Moreover, overexpression of mTOR inhibits OPN-induced NF-kappaB and AP-1-DNA binding and transcriptional activity. However, rapamycin further enhanced these OPN-induced effects. We also report that OPN induces p70S6 kinase phosphorylation at Thr-421/Ser-424, but not at Thr-389 or Ser-371 and mTOR phosphorylation at Ser-2448. Overexpression of mTOR has no effect in regulation of OPN-induced phosphorylation of p70S6 kinase at Thr-421/Ser-424. Inhibition of mTOR by rapamycin attenuates Ser-371 phosphorylation but does not have any effect on Thr-389 and Thr-421/Ser-424 phosphorylation of p70S6 kinase. However, OPN-induced phosphorylation of p70S6 kinase at Thr-421/Ser-424 is being controlled by MEK/ERK pathway.


CONCLUSIONS
These results suggest that blocking of OPN-induced ICAM-1 expression through mTOR/p70S6 kinase signaling pathway may be an important therapeutic strategy for the treatment of breast cancer.
Ahmed
Mansoor
M
National Center for Cell Science (NCCS), NCCS Complex, Pune 411 007, India.
Kundu
Gopal C
GC
D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D024202:Electrophoretic Mobility Shift Assay; D004789:Enzyme Activation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000096:biosynthesis* / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D053495:Osteopontin / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D020239:Receptor Cross-Talk; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; D018808:Transcription Factor AP-1; D053495:Osteopontin; D018799:Intercellular Adhesion Molecule-1; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases
FEBS Lett. 1997 Jun 23;410(1):78-82
9247127
Carcinogenesis. 2005 May;26(5):943-50
15774488
Cancer Sci. 2003 Jul;94(7):575-81
12841864
J Biol Chem. 2004 Mar 19;279(12):11051-64
14704150
Curr Mol Med. 2006 Dec;6(8):819-30
17168734
Nat Rev Drug Discov. 2004 Jan;3(1):17-26
14708018
J Biol Chem. 2002 May 31;277(22):20104-12
11914378
J Biol Chem. 2000 Mar 10;275(10):7416-23
10702316
Nat Med. 2003 Jan;9(1):16-8
12514712
Science. 2001 Nov 2;294(5544):1102-5
11691993
Osteoporos Int. 1993;3 Suppl 1:132-5
8461540
Curr Opin Pharmacol. 2003 Aug;3(4):371-7
12901945
J Biol Chem. 2003 Apr 18;278(16):14487-97
12473670
Int J Oncol. 2004 May;24(5):1235-44
15067347
J Biol Chem. 1995 Sep 8;270(36):21396-403
7545671
Crit Rev Oral Biol Med. 2000;11(3):279-303
11021631
Proc Natl Acad Sci U S A. 1992 Aug 1;89(15):7282-6
1496022
Oncogene. 2002 Aug 8;21(34):5213-23
12149643
Biochem J. 1999 Dec 1;344 Pt 2:427-31
10567225
Cancer Res. 2002 Jun 15;62(12):3417-27
12067984
JOP. 2009 Jan 08;10(1):8-14
19129609
J Biol Chem. 2003 Aug 1;278(31):28593-606
12771144
Mol Cell Biol. 2002 Sep;22(18):6321-35
12192032
Genes Dev. 2004 Aug 15;18(16):1926-45
15314020
Carcinogenesis. 2010 Feb;31(2):192-200
19926637
J Immunol. 2005 May 1;174(9):5823-9
15843586
Mol Cell Biol. 1997 Sep;17(9):5648-55
9271440
J Biol Chem. 2004 Sep 10;279(37):38921-35
15247285
Cancer Res. 2004 Dec 15;64(24):8906-10
15604251
Cell. 1994 Jul 15;78(1):35-43
7518356
Expert Opin Investig Drugs. 2005 Mar;14(3):313-28
15833062
Proc Natl Acad Sci U S A. 1995 Jun 6;92(12):5744-8
7777579
J Mol Med (Berl). 1997 Jun;75(6):429-39
9231883
Mol Cell Biol. 2004 Sep;24(17):7806-19
15314185
J Biol Chem. 2001 Nov 30;276(48):44926-35
11564733
Cancer Res. 2008 Jan 1;68(1):152-61
18172307
Proc Natl Acad Sci U S A. 1997 Aug 19;94(17):9308-13
9256478
J Biol Chem. 2005 Jul 22;280(29):27366-74
15917256
Cancer Gene Ther. 2004 Feb;11(2):109-20
14647232
Trends Cell Biol. 2006 Feb;16(2):79-87
16406521