Format

Send to

Choose Destination
Breast Cancer Res. 2016 Feb 26;18(1):26. doi: 10.1186/s13058-016-0686-4.

Mcl-1 confers protection of Her2-positive breast cancer cells to hypoxia: therapeutic implications.

Author information

1
Department of Medical Oncology, National Center for Tumor Diseases (NCT), University of Heidelberg, Im Neuenheimer Feld #460, Heidelberg, 69120, Germany.
2
Department of Pharmacology and Therapy, Faculty of Medicine, Universitas Padjadjaran, Jl. Eijkman 38, Bandung, 02215, Indonesia.
3
Dana-Farber Cancer Institute, 450 Brookline Avenue, Boston, MA, 02215, USA.
4
Eutropics, Inc., 767C Concord Avenue, Cambridge, MA, 02138, USA.
5
German Cancer Research Center (DKFZ), Im Neuenheimer Feld 460, 69120, Heidelberg, Germany.
6
St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN, 38105, USA.
7
Department of Medical Oncology, National Center for Tumor Diseases (NCT), University of Heidelberg, Im Neuenheimer Feld #460, Heidelberg, 69120, Germany. klaus.podar@nct-heidelberg.de.

Abstract

BACKGROUND:

Molecular mechanisms leading to the adaptation of breast cancer (BC) cells to hypoxia are largely unknown. The anti-apoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1) is frequently amplified in BC; and elevated Mcl-1 levels have been correlated with poor prognosis. Here we investigated the pathophysiologic role of Mcl-1 in Her2-positive BC cells under hypoxic conditions.

METHODS:

RNA interference and a novel small molecule inhibitor, EU-5346, were used to examine the role of Mcl-1 in Her2-positive BC cell lines and primary BC cells (sensitive or intrinsically resistant to Her2 inhibitors) under hypoxic conditions (using a hypoxic incubation chamber). Mechanisms-of-action were investigated by RT-PCR, mitochondrial isolation, as well as immunoprecipitation/blotting analysis, and microscopy. The specificity against Mcl-1 of the novel small molecule inhibitor EU5346 was verified in Mcl-1(Δ/null) versus Mcl-1(wt/wt) Murine Embryonic Fibroblasts (MEFs). Proliferation, survival, and spheroid formation were assessed in response to Mcl-1 and Her2 inhibition.

RESULTS:

We demonstrate for a strong correlation between high Mcl-1 protein levels and hypoxia, predominantly in Her2-positive BC cells. Surprisingly, genetic depletion of Mcl-1 decreased Her2 and Hif-1α levels followed by inhibition of BC cell survival. In contrast, Mcl-1 protein levels were not downregulated after genetic depletion of Her2 indicating a regulatory role of Mcl-1 upstream of Her2. Indeed, Mcl-1 and Her2 co-localize within the mitochondrial fraction and form a Mcl-1/Her2- protein complex. Similar to genetically targeting Mcl-1 the novel small molecule Mcl-1 inhibitor EU-5346 induced cell death and decreased spheroid formation in Her2-positive BC cells. Of interest, EU-5346 induced ubiquitination of Mcl-1- bound Her2 demonstrating a previously unknown role for Mcl-1 to stabilize Her2 protein levels. Importantly, targeting Mcl-1 was also active in Her2-positive BC cells resistant to Her2 inhibitors, including a brain-primed Her2-positive cell line.

CONCLUSION:

Our data demonstrate a critical role of Mcl-1 in Her2-positive BC cell survival under hypoxic conditions and provide the preclinical framework for the therapeutic use of novel Mcl-1- targeting agents to improve patient outcome in BC.

PMID:
26921175
PMCID:
PMC4769490
DOI:
10.1186/s13058-016-0686-4
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for BioMed Central Icon for PubMed Central
Loading ...
Support Center