The macrophage inhibitory cytokine integrates AKT/PKB and MAP kinase signaling pathways in breast cancer cells.
Macrophage inhibitory cytokine 1 (MIC-1), a divergent member of the transforming growth factor beta superfamily, plays a role in the progression of a number of cancers, including breast, gastric, prostate and colorectal carcinomas. Serum MIC-1 levels are elevated in patients with metastatic prostate, breast and colorectal carcinomas. In vitro studies have revealed a cell type-specific role for MIC-1 in senescence and apoptosis. MIC-1 activates the survival kinase AKT/PKB in neuronal cells. Depending on the cell type, it activates or represses the MAP kinases ERK1/2. Mechanisms responsible for an increased MIC-1 expression in cancers and the consequences of MIC-1 overexpression, however, are not known. In this study, we show that AKT/PKB directly regulates the expression of MIC-1 in breast cancer cells. Sequences within -88 to +30 of the MIC-1 promoter are required for the AKT-mediated induction of MIC-1. This region of the promoter contains two SP-1 binding sites (SP-1B and SP-1C), which bind to the SP-1 and SP-3 proteins. Mutation of SP-1C but not SP-1B reduced the AKT-mediated activation of MIC-1. MIC-1 increased the basal ERK1 phosphorylation and prolonged the estrogen-stimulated ERK1 phosphorylation in MCF-7 breast cancer cells without altering the phosphorylation status of AKT/PKB. Immunohistochemistry with MIC-1 antibody revealed an MIC-1 expression within the cancer cells of primary breast cancer and in the MCF-7 xenografts. Furthermore, a limited analysis of RNA from primary breast cancers revealed an overexpression of MIC-1 in tumors, compared with normal tissues. These results suggest that AKT/PKB through MIC-1 could regulate the ERK1 activity and the MIC-1 expression levels may serve as a surrogate marker for the AKT activation in tumors.
Wollmann
Wyatt
W
Department of Surgery, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Goodman
Mike L
ML
Bhat-Nakshatri
Poornima
P
Kishimoto
Hiromitsu
H
Goulet
Robert J
RJ
Mehrotra
Sanjana
S
Morimiya
Akira
A
Badve
Sunil
S
Nakshatri
Harikrishna
H
D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism*; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D024202:Electrophoretic Mobility Shift Assay; D005260:Female; D055436:Growth Differentiation Factor 15; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000502:physiology
D016207:Cytokines; C526140:GDF15 protein, human; D055436:Growth Differentiation Factor 15; D011518:Proto-Oncogene Proteins; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases