title: Myeloid cell leukemia-1 is an important apoptotic survival factor in triple-negative breast cancer.
abstract: Breast cancer is the second-most frequently diagnosed malignancy in US women. The triple-negative breast cancer (TNBC) subtype, which lacks expression of the estrogen receptor, progesterone receptor and human epidermal growth factor receptor-2, afflicts 15% of patients and is refractory to current targeted therapies. Like many cancers, TNBC cells often deregulate programmed cell death by upregulating anti-apoptotic proteins of the B-cell CLL/lymphoma 2 (Bcl-2) family. One family member, myeloid cell leukemia-1 (Mcl-1), is commonly amplified in TNBC and correlates with a poor clinical prognosis. Here we show the effect of silencing Mcl-1 and Bcl-2-like protein 1 isoform 1 (Bcl-xL) expression on viability in a panel of seventeen TNBC cell lines. Cell death was observed in a subset upon Mcl-1 knockdown. In contrast, Bcl-xL knockdown only modestly reduced viability, indicating that Mcl-1 is a more important survival factor. However, dual silencing of both Mcl-1 and Bcl-xL reduced viability in most cell lines tested. These proliferation results were recapitulated by BH3 profiling experiments. Treatment with a Bcl-xL and Bcl-2 peptide had only a moderate effect on any of the TNBC cell lines, however, co-dosing an Mcl-1-selective peptide with a peptide that inhibits Bcl-xL and Bcl-2 was effective in each line tested. Similarly, the selective Bcl-xL inhibitor WEHI-539 was only weakly cytotoxic across the panel, but sensitization by Mcl-1 knockdown markedly improved its EC50. ABT-199, which selectively inhibits Bcl-2, did not synergize with Mcl-1 knockdown, indicating the relatively low importance of Bcl-2 in these lines. Mcl-1 sensitivity is not predicted by mRNA or protein levels of a single Bcl-2 family member, except for only a weak correlation for Bak and Bax protein expression. However, a more comprehensive index composed of Mcl-1, Bcl-xL, Bim, Bak and Noxa protein or mRNA expression correlates well with Mcl-1 sensitivity in TNBC and can also predict Mcl-1 dependency in non-small cell lung cancer cell lines.
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Goodwin
authors.affiliation: Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN, USA.|Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: O W
authors.initials: OW
authors.lastname: Rossanese
authors.affiliation: Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN, USA.|Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: E T
authors.initials: ET
authors.lastname: Olejniczak
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN, USA.|Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN, USA.|Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: S W
authors.initials: SW
authors.lastname: Fesik
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D064726:Triple Negative Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D019086:Bridged Bicyclo Compounds, Heterocyclic; C579095:MCL1 protein, human; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C498702:PMAIP1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D013449:Sulfonamides; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C579720:venetoclax