Bag-1 stimulates Bad phosphorylation through activation of Akt and Raf kinases to mediate cell survival in breast cancer

Abstract

BackgroundBag-1 (Bcl-2-associated athanogene) is a multifunctional anti-apoptotic protein frequently overexpressed in cancer. Bag-1 interacts with a variety of cellular targets including Hsp70/Hsc70 chaperones, Bcl-2, nuclear hormone receptors, Akt and Raf kinases. In this study, we investigated in detail the effects of Bag-1 on major cell survival pathways associated with breast cancer.MethodsUsing immunoblot analysis, we examined Bag-1 expression profiles in tumor and normal tissues of breast cancer patients with different receptor status. We investigated the effects of Bag-1 on cell proliferation, apoptosis, Akt and Raf kinase pathways, and Bad phosphorylation by implementing ectopic expression or knockdown of Bag-1 in MCF-7, BT-474, MDA-MB-231 and MCF-10A breast cell lines. We also tested these in tumor and normal tissues from breast cancer patients. We investigated the interactions between Bag-1, Akt and Raf kinases in cell lines and tumor tissues by co-immunoprecipitation, and their subcellular localization by immunocytochemistry and immunohistochemistry.ResultsWe observed that Bag-1 is overexpressed in breast tumors in all molecular subtypes, i.e., regardless of their ER, PR and Her2 expression profile. Ectopic expression of Bag-1 in breast cancer cell lines results in the activation of B-Raf, C-Raf and Akt kinases, which are also upregulated in breast tumors. Bag-1 forms complexes with B-Raf, C-Raf and Akt in breast cancer cells, enhancing their phosphorylation and activation, and ultimately leading to phosphorylation of the pro-apoptotic Bad protein at Ser112 and Ser136. This causes Bad’s re-localization to the nucleus, and inhibits apoptosis in favor of cell survival.ConclusionsOverall, Bad inhibition by Bag-1 through activation of Raf and Akt kinases is an effective survival and growth strategy exploited by breast cancer cells. Therefore, targeting the molecular interactions between Bag-1 and these kinases might prove an effective anticancer therapy.

Prognostic Value of an Autophagy-Related Five-Gene Signature for Lower-Grade Glioma Patients

“…BAG1 is an oncogene that can enhance the anti-apoptotic effect of BLC-2 ( 26 ) and is aberrantly expressed in multiple cancer types. It has been suggested that BAG1 can be used as a potential drug target ( 27 ). BID is a member of the BCL-2 family and promotes apoptosis ( 28 ).…”

Bcl-2 Associated Athanogene 2 (BAG2) is Associated With Progression and Prognosis of Hepatocellular Carcinoma: A Bioinformatics-Based Analysis

“…For instance, cetuximab targeting epidermal growth factor receptor (EGFR), bevacizumab against vascular endothelial growth factor receptor (VEGFR), and dabrafenib inhibiting BRAF V600E mutation has become cornerstone of anti-tumor treatments and considerably improve the prognosis of advanced cancer patients [24][25][26]. The BAG family, which is evolutionarily conserved, might serve as a new potential therapeutic target in cancer treatment since studies show that members of this family are related to chemo-resistance, invasion and apoptosis of tumors [27][28][29][30][31]. For instance, Tugba Kizilboga et al reported that BAG1 favored survival of breast cancer cells by phosphorylating the proapoptotic Bad protein through activation of the Akt and Raf kinase pathways [30].…”

“…The BAG family, which is evolutionarily conserved, might serve as a new potential therapeutic target in cancer treatment since studies show that members of this family are related to chemo-resistance, invasion and apoptosis of tumors [27][28][29][30][31]. For instance, Tugba Kizilboga et al reported that BAG1 favored survival of breast cancer cells by phosphorylating the proapoptotic Bad protein through activation of the Akt and Raf kinase pathways [30]. Anja Bruchmann et al found that BAG5 was over-expressed in prostate cancer and played a role in preventing stress-induced cell death [31].…”

Co-Chaperone Bag-1 Plays a Role in the Autophagy-Dependent Cell Survival through Beclin 1 Interaction

“…Bag-1 overexpression upregulates one of the main apoptosis regulator Bcl-2 in Jurkat cells [19,21], while its downregulation decreases Bcl-2 levels in cervical cells [22]. The formation of Bag-1/Bcl-2 complex activates the Ras/Raf/MEK/ERK pathway, which controls the transcription of cell survival genes [23,24]. Hence, Bag-1 functions as an anti-apoptotic protein involved in both activation of cell survival and inhibition of cell death through a variety of mechanisms [12,19,22,25].…”

“…Bcl-2 is a major anti-apoptotic protein and is elevated in about 75% of primary breast tumors from human patients [26]. It functions through the formation of homodimers and heterodimers, especially with Bag-1, Bax, Bad, Bak, Beclin 1 and Raf-1 [22,24,25]. The association of Bcl-2 with the autophagy regulator Beclin 1 modulates the switch between apoptosis and autophagy pathways [27,28].…”