Osteopontin regulates ubiquitin-dependent degradation of Stat1 in murine mammary epithelial tumor cells.
BACKGROUND
Osteopontin (OPN) is a secreted glycoprotein that mediates cell-matrix interactions and cellular signaling by binding with integrin (primarily alpha(v)beta(3)) and CD44 receptors. OPN regulates cell adhesion, chemotaxis, macrophage-directed IL-10 suppression, stress-dependent angiogenesis, apoptosis prevention, and anchorage-independent growth of tumor cells. However, the molecular mechanisms that define the role of OPN in tumor progression and metastasis are incompletely understood.


METHODS
In this study, we use a system of 4T1 and 4T07 murine mammary epithelial tumor cell lines that are divergent in both metastatic phenotype and OPN expression. 4T1 expresses OPN and hematogeneously metastasizes, whereas 4T07 does not express OPN and is highly tumorigenic but fails to metastasize.


RESULTS
Our results demonstrate that OPN regulates Stat1 protein degradation through the ubiquitin-proteasome pathway to alter interferon-gamma-dependent growth inhibition and p21 expression. We identify Stat-interacting LIM protein as the critical Stat ubiquitin E3 ligase in this setting.


CONCLUSIONS
OPN regulates Stat1-dependent functions, such as growth inhibition and p21 expression, in the murine mammary epithelial cells lines 4T1 and 4T07. This relationship between OPN and Stat1 in the context of tumor biology has not been previously examined.
Gao
Chengjiang
C
Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.
Mi
Zhiyong
Z
Guo
Hongtao
H
Kuo
Paul C
PC
D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology; D000818:Animals; D002455:Cell Division; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D007371:Interferon-gamma / Q000494:pharmacology; D060588:LIM Domain Proteins; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D009362:Neoplasm Metastasis; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D053495:Osteopontin / Q000037:antagonists & inhibitors / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; D060588:LIM Domain Proteins; D009363:Neoplasm Proteins; C508508:Pdlim2 protein, mouse; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D050794:STAT1 Transcription Factor; C506896:Spp1 protein, mouse; C494080:Stat1 protein, mouse; D025801:Ubiquitin; D053495:Osteopontin; D007371:Interferon-gamma; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease