AKT3 regulates ErbB2, ErbB3 and estrogen receptor 伪 expression and contributes to endocrine therapy resistance of ErbB2⁺ breast tumor cells from Balb-neuT mice

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• 作者：Nicole Grabinski^a ; Katharina Mö ; llmann^b ; ¹ ; Karin Milde-Langosch^c ; Volkmar Mü ; ller^c ; Udo Schumacher^d ; Burkhard Brandt^b ; ² ; Klaus Pantel^b ; Manfred Jü ; cker^a ; ^{juecker@uke.uni-hamburg.de" class="auth_mail}
• 关键词：AKT ; ErbB2 ; Estrogen receptor 伪 ; Therapy resistance ; Breast cancer ; Balb-neuT mice
• 刊名：Cellular Signalling
• 出版年：May, 2014
• 年：2014
• 卷：26
• 期：5
• 页码：1021-1029
• 全文大小：785 K

文摘

ErbB2⁺ breast cancer is an aggressive breast cancer subtype generally associated with lower estrogen receptor alpha (ER伪) expression and more aggressive tumor behavior compared to ER伪⁺/ErbB2^{鈭?/sup> 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 ER伪 was strongly up-regulated and phosphorylation of the AKT substrate Foxo3a which regulates ER伪 transcription was decreased in AKT3 knockdown cells. These data suggest that ER伪 expression is down regulated via AKT3/Foxo3a signaling in ErbB2+ breast cancer cells. Furthermore, up-regulation of ER伪 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 ER伪+ breast cancer. Our data indicate that AKT3 regulates the expression of ErbB2, ErbB3 and ER伪 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+/ER伪鈭?/sup> breast cancer and might further increase the responsiveness to an endocrine therapy approach.}