Jab1 is a target of EGFR signaling in ERalpha-negative breast cancer.
BACKGROUND
c-Jun activation domain-binding protein-1 (Jab1) is a multifunctional signaling protein that previously has been shown to be a master regulator of a poor prognostic gene signature in invasive breast cancer and to mediate the action of S100A7. Since epidermal growth factor receptor (EGFR), like S100A7, is often expressed in estrogen receptor-alpha-negative (ERalpha-) breast cancer, we set out to investigate the role of Jab1 in mediating EGFR signaling, another facet of the ERalpha- phenotype.


METHODS
MDA-MB-231 and MDA-MB-468 ERalpha-/EGFR+ cell lines were assessed for localization of Jab1 and levels of downstream genes by immunofluorescence and nuclear protein extract assay following treatment with epidermal growth factor (EGF) and extracellular signal-regulated kinase (ERK) pathway inhibitor. A cohort of 424 human breast tumors was also assessed by immunohistochemistry.


RESULTS
EGF treatment of cell lines resulted in increased Jab1 nuclear expression. This effect was inhibited by the ERK pathway inhibitor, PD98059. EGF treatment was also associated with colocalization of pERK (phosphorylated ERK) and Jab1 as well as regulation of the Jab1 downstream target gene, p27. When Jab1 activity was knocked down, p27 levels were restored to pre-EGF treatment level. Analysis of EGFR and Jab1 expression in a cohort of invasive breast tumors by tissue microarray and immunohistochemistry confirmed a relationship between EGFR and increased nuclear Jab1 within the ERalpha- subset (n = 154, P = 0.019). The same association was also confirmed for S100A7 and Jab1 (P = 0.036), and high Jab1 nuclear expression was most frequent in tumors that were positive for both EGFR and S100A7 (P = 0.004).


CONCLUSIONS
Jab1 is a target of EGFR signaling in ERalpha- cell lines and breast tumors and therefore may be a common central factor and potential therapeutic target for important cell signaling pathways in ERalpha- breast cancer.
Deeley Research Center, BC Cancer Agency, Vancouver Island Center, Victoria, BC, Canada.
Jiaxu
J
Wang
Rebecca O
RO
Barnes
Nathan R
NR
West
Melanie
M
Olson
Jenny E
JE
Chu
Peter H
PH
Watson
D001943:Breast Neoplasms / Q000378:metabolism*; D000075686:COP9 Signalosome Complex; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D015331:Cohort Studies; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D047628:Estrogen Receptor alpha / Q000096:biosynthesis*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D010447:Peptide Hydrolases / Q000096:biosynthesis* / Q000378:metabolism; D015398:Signal Transduction
D004791:Enzyme Inhibitors; D047628:Estrogen Receptor alpha; D005419:Flavonoids; D047908:Intracellular Signaling Peptides and Proteins; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; D010447:Peptide Hydrolases; C501488:COPS5 protein, human; D000075686:COP9 Signalosome Complex; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one