HIF1α-Induced by Lysophosphatidic Acid Is Stabilized via Interaction with MIF and CSN5.
Macrophage migration inhibitory factor (MIF) is a cytokine that has broad effects on immune system and inflammatory response. A growing body of evidence implicates the role of MIF in tumor growth and metastasis. Lysophosphatidic acid (LPA), a bioactive lipid mediator, regulates colon cancer cell proliferation, invasion, and survival through LPA2 receptor. Loss of LPA2 results in decreased expression of MIF in a rodent model of colon cancer, but the mechanism of MIF regulation by LPA is yet to be determined. In this study, we show that LPA transcriptionally regulates MIF expression in colon cancer cells. MIF knockdown decreased LPA-mediated proliferation of HCT116 human adenocarcinoma cells without altering the basal proliferation rates. Conversely, extracellular recombinant MIF stimulated cell proliferation, suggesting that the effect of MIF may in part be mediated through activation of surface receptor. We have shown recently that LPA increases hypoxia-inducible factor 1α (HIF1α) expression. We found that MIF regulation by LPA was ablated by knockdown of HIF1α, indicating that MIF is a transcriptional target of HIF1α. Conversely, knockdown of MIF ablated an increase in HIF1α expression in LPA-treated cells, suggesting a reciprocal relationship between HIF1α and MIF. LPA stimulated co-immunoprecipitation of HIF1α and MIF, indicating that their association is necessary for stabilization of HIF1α. It has been shown previously that CSN9 signalosome subunit 5 (CSN5) interacts with HIF1α to stabilize HIF1α under aerobic conditions. We found that LPA did not alter expression of CSN5, but stimulated its interaction with HIF1α and MIF. Depletion of CSN5 mitigated the association between HIF1α and MIF, indicating that CSN5 acts as a physical link. We suggest that HIF1α, MIF, and CSN5 form a ternary complex whose formation is necessary to prevent degradation of HIF1α under aerobic conditions.
Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, Georgia, United States of America.
Yi Ran
YR
No
Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, Georgia, United States of America.
Sei-Jung
SJ
Lee
Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, Georgia, United States of America.
Ajay
A
Kumar
Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, Georgia, United States of America; Winship Cancer Institute, Emory University, Atlanta, Georgia, United States of America.
C Chris
CC
Yun
D000075686:COP9 Signalosome Complex; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D019746:Intramolecular Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D008246:Lysophospholipids / Q000494:pharmacology*; D008263:Macrophage Migration-Inhibitory Factors / Q000235:genetics / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047908:Intracellular Signaling Peptides and Proteins; D008246:Lysophospholipids; D008263:Macrophage Migration-Inhibitory Factors; D010447:Peptide Hydrolases; C501488:COPS5 protein, human; D000075686:COP9 Signalosome Complex; D019746:Intramolecular Oxidoreductases; C515598:MIF protein, human; C032881:lysophosphatidic acid