The opioid growth factor-opioid growth factor receptor axis regulates cell proliferation of human hepatocellular cancer

Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide, with a mortality rate approximating its incidence. Understanding the biology of these tumors, as well as treatment modalities, has been challenging. The opioid growth factor (OGF; [Met5]-enkephalin) and the OGF receptor (OGFr) form an endogenous growth-regulating pathway in homeostasis and neoplasia. In this investigation, we examined the relationship of the OGF-OGFr axis in HCC and define its presence, function, and mechanism. Using SK-HEP-1, Hep G2, and Hep 3B human HCC cell lines, we found that OGF and OGFr were present and functional. Exogenous OGF was observed to have a dose-dependent, reversible, and receptor-mediated inhibitory action on cell proliferation. Endogenous OGF was found to be constitutively produced and tonically active on cell replicative activities, with neutralization of this peptide accelerating cell proliferation. Silencing of OGFr using siRNA stimulated cell replication, even when exogenous OGF was added to the cultures, documenting its importance in mediating OGF activity. The mechanism of OGF-OGFr action on cell number was related to inhibition of DNA synthesis and not to apoptotic or necrotic pathways. Both OGF and OGFr were detected in surgical specimens of HCC, and no quantitative differences were recorded in peptide or receptor between pathological and normal specimens. These data are the first to report that the OGF-OGFr system is a native biological regulator of cell proliferation in HCC. The findings may provide important insight in designing treatment strategies for this deadly disease.

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Opioid growth factor-opioid growth factor receptor axis is a physiological determinant of cell proliferation in diverse human cancers

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00414.2009 ◽

2009 ◽

Vol 297 (4) ◽

pp. R1154-R1161 ◽

Cited By ~ 45

Author(s):

Ian S. Zagon ◽

Renee N. Donahue ◽

Patricia J. McLaughlin

Keyword(s):

Cell Proliferation ◽

Growth Factor ◽

Cancer Cells ◽

Human Cancer ◽

Growth Factor Receptor ◽

Cell Number ◽

Treatment Modalities ◽

Human Cancer Cell Lines ◽

Human Cancer Cells ◽

Opioid Growth Factor

The opioid growth factor (OGF) regulates cell proliferation of human cancer cells through the cyclin-dependent kinase inhibitory pathway, with mediation of this action by the OGF receptor (OGFr). The ubiquity of the OGF-OGFr axis in human cancer is unknown. We used 31 human cancer cell lines, representative of more than 90% of neoplasias occurring in humans, and found that OGF and OGFr were detected in the cytoplasm and nucleus by immunohistochemistry. The addition of OGF to cultures depressed cell number up to 41%, whereas naltrexone (NTX) increased cell proliferation by up to 44%, a total of 85% in the modulating capacity for the OGF-OGFr axis. Neutralization of OGF by specific antibodies led to a marked increase in cell number. Knockdown of OGFr by OGFr-siRNA resulted in a significant increase in the number of cells, even in the face of the addition of exogenous OGF. The cultures to which NTX was added and subjected to OGFr-siRNA were similar to those with OGF-siRNA alone. The OGF-OGFr axis, a physiological determinant of cell-proliferative activity, is a ubiquitous feature of human cancer cells. The identification of this native biological system in neoplasia may be important in understanding the pathophysiology of neoplasia, and in designing treatment modalities that utilize the body's own chemistry.

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Overexpression of the opioid growth factor receptor downregulates cell proliferation of human squamous carcinoma cells of the head and neck

International Journal of Molecular Medicine ◽

10.3892/ijmm.19.3.421 ◽

2007 ◽

Cited By ~ 4

Author(s):

Patricia McLaughlin ◽

Michael Verderame ◽

Jody Hankins ◽

Ian Zagon

Keyword(s):

Cell Proliferation ◽

Growth Factor ◽

Head And Neck ◽

Growth Factor Receptor ◽

Squamous Carcinoma ◽

Carcinoma Cells ◽

Opioid Growth Factor ◽

Squamous Carcinoma Cells

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Regulation of Tenon's Capsule Fibroblast Cell Proliferation by the Opioid Growth Factor and the Opioid Growth Factor Receptor Axis

Investigative Opthalmology & Visual Science ◽

10.1167/iovs.09-4949 ◽

2010 ◽

Vol 51 (10) ◽

pp. 5054 ◽

Cited By ~ 3

Author(s):

Matthew S. Klocek ◽

Joseph W. Sassani ◽

Renee N. Donahue ◽

Patricia J. McLaughlin ◽

Ian S. Zagon

Keyword(s):

Cell Proliferation ◽

Growth Factor ◽

Growth Factor Receptor ◽

Fibroblast Cell ◽

Opioid Growth Factor ◽

Tenon’S Capsule ◽

Tenon's Capsule

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Particle-Mediated Gene Transfer of Opioid Growth Factor Receptor cDNA Regulates Cell Proliferation of the Corneal Epithelium

Cornea ◽

10.1097/01.ico.0000153561.89902.57 ◽

2005 ◽

Vol 24 (5) ◽

pp. 614-619 ◽

Cited By ~ 16

Author(s):

Ian S Zagon ◽

Joseph W Sassani ◽

Michael F Verderame ◽

Patricia J McLaughlin

Keyword(s):

Cell Proliferation ◽

Growth Factor ◽

Gene Transfer ◽

Corneal Epithelium ◽

Growth Factor Receptor ◽

Opioid Growth Factor ◽

Receptor Cdna

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Dependence on Nuclear Localization Signals of the Opioid Growth Factor Receptor in the Regulation of Cell Proliferation

Experimental Biology and Medicine ◽

10.3181/0901-rm-16 ◽

2009 ◽

Vol 234 (5) ◽

pp. 532-541 ◽

Cited By ~ 27

Author(s):

Fan Cheng ◽

Patricia J. McLaughlin ◽

Michael F. Verderame ◽

Ian S. Zagon

Keyword(s):

Cell Proliferation ◽

Growth Factor ◽

Nuclear Localization ◽

Fluorescent Protein ◽

Growth Factor Receptor ◽

Full Length ◽

Nuclear Pore ◽

Nucleocytoplasmic Trafficking ◽

Nuclear Localization Signals ◽

Opioid Growth Factor

The opioid growth factor receptor (OGFr) mediates the inhibitory action of OGF on cell replication of normal and neoplastic cells. The spatiotemporal course of OGFr nucleocytoplasmic trafficking was determined with a probe of full-length OGFr fused to enhanced green fluorescent protein (eGFP). Translation of OGFr required 8.5 hours, and transit into the nucleus required 8 hours; OGFr remained in the nucleus for 8 days. OGFr was initially expressed on the outer nuclear envelope, transited to the paranuclear cytoplasm, and into the nucleus. Transport through the nuclear pore was elucidated by mutation of the nuclear localization signal (NLS) sequences in full-length OGFr. Mutation of each NLS reduced nuclear localization by 5%–50%, whereas simultaneous mutation of NLS383–386 and NLS456–460 abolished OGFr-eGFP nuclear localization in 80% of the cells. To determine whether intact NLSs are important for the inhibition of cell proliferation, DNA synthesis was monitored with BrdU. Wild-type OGFr-eGFP–transfected cells had 20% BrdU-positive cells, whereas cells with simultaneous mutation of all three NLS sites had a 70% labeling index. These results indicate that the regulation of cell proliferation by the OGF-OGFr axis is dependent on nucleocytoplasmic translocation and reliant on the integrity of two NLSs in OGFr to interact with transport receptors.

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