AKT3 regulates ErbB2, ErbB3 and estrogen receptor α expression and contributes to endocrine therapy resistance of ErbB2(+) breast tumor cells from Balb-neuT mice.
ErbB2(+) breast cancer is an aggressive breast cancer subtype generally associated with lower estrogen receptor alpha (ERα) expression and more aggressive tumor behavior compared to ERα(+)/ErbB2(-) breast cancer. The ErbB2(+) phenotype is associated with resistance to endocrine therapy, e.g. the selective estrogen receptor modulator Tamoxifen. However, the mechanisms underlying endocrine resistance are not fully understood. Here, we investigated the impact of AKT signaling and distinct functional roles of AKT isoforms in ErbB2(+) breast cancer from Balb-neuT mice. AKT isoform specific in vitro kinase assays revealed that AKT3 is activated in Balb-neuT breast tumors in comparison to normal murine breast tissue. Knock-down of AKT3, but not of AKT1 or AKT2, led to reduced expression and tyrosine-phosphorylation of ErbB2 and ErbB3 in Balb-neuT-derived mammary tumor cells. In contrast, expression of ERα was strongly up-regulated and phosphorylation of the AKT substrate Foxo3a which regulates ERα transcription was decreased in AKT3 knockdown cells. These data suggest that ERα expression is down regulated via AKT3/Foxo3a signaling in ErbB2(+) breast cancer cells. Furthermore, up-regulation of ERα after depletion of AKT3 resulted in a significant increase in Tamoxifen responsiveness of Balb-neuT-derived mammary tumor cells. In addition, Tamoxifen resistant human breast cancer cell lines showed increased AKT3 expression and activity in comparison to Tamoxifen responsive MCF-7 cells. Finally, by AKT isoform specific in vitro kinase assays of human breast cancer samples, AKT3 activity was detected in ErbB2(+) and triple negative tumors but not in ERα(+) breast cancer. Our data indicate that AKT3 regulates the expression of ErbB2, ErbB3 and ERα and demonstrate that down-regulation of activated AKT3 can sensitize ErbB2(+) breast cancer cells for treatment with Tamoxifen. Therefore, AKT3 targeting might be a new promising strategy for therapy of ErbB2(+)/ERα(-) breast cancer and might further increase the responsiveness to an endocrine therapy approach.
Institute of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Nicole
N
Grabinski
Institute of Tumor Biology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Katharina
K
Möllmann
Department of Gynecology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Karin
K
Milde-Langosch
Department of Gynecology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Volkmar
V
Müller
Institute of Anatomy, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Udo
U
Schumacher
Institute of Tumor Biology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Burkhard
B
Brandt
Institute of Tumor Biology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Klaus
K
Pantel
Institute of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany. Electronic address: juecker@uke.uni-hamburg.de.
Manfred
M
Jücker
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D005260:Female; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D061986:MCF-7 Cells; D051379:Mice; D008822:Mice, Transgenic; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D020893:Receptor, ErbB-3 / Q000378:metabolism*; D013629:Tamoxifen / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects
D000970:Antineoplastic Agents; D047628:Estrogen Receptor alpha; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3; D013629:Tamoxifen; C474033:FoxO3 protein, mouse
AKT; Balb-neuT mice; Breast cancer; ErbB2; Estrogen receptor α; Therapy resistance