Inhibiting BCKDK in triple negative breast cancer suppresses protein translation, impairs mitochondrial function, and potentiates doxorubicin cytotoxicity

Abstract

Triple-negative breast cancers (TNBCs) are characterized by poor survival, prognosis, and gradual resistance to cytotoxic chemotherapeutics, like doxorubicin (DOX). The clinical utility of DOX is limited by its cardiotoxic and chemoresistant effects that manifest over time. To induce chemoresistance, TNBC rewires oncogenic gene expression and cell signaling pathways. Recent studies have demonstrated that reprogramming of branched-chain amino acids (BCAAs) metabolism facilitates tumor growth and survival. Branched-chain ketoacid dehydrogenase kinase (BCKDK), a regulatory kinase of the rate-limiting enzyme of the BCAA catabolic pathway, is reported to activate RAS/RAF/MEK/ERK signaling to promote tumor cell proliferation. However, it remains unexplored if BCKDK action remodels TNBC proliferation and survival per se and influences susceptibility to DOX-induced genotoxic stress. TNBC cells treated with DOX exhibited reduced BCKDK expression and intracellular BCKAs. Genetic and pharmacological inhibition of BCKDK in TNBC cell lines also showed a similar reduction in intracellular and secreted BCKAs. BCKDK silencing in TNBC cells downregulated mitochondrial metabolism genes, reduced electron complex protein expression, oxygen consumption, and ATP production. Transcriptome analysis of BCKDK silenced cells confirmed dysregulation of mitochondrial metabolic networks and upregulation of the apoptotic signaling pathway. Furthermore, BCKDK inhibition with concurrent DOX treatment exacerbated apoptosis, caspase activity, and loss of TNBC proliferation. Inhibition of BCKDK in TNBC also upregulated sestrin 2 and concurrently decreased mTORC1 signaling and protein synthesis. Overall, loss of BCKDK action in TNBC remodels BCAA flux, reduces protein translation triggering cell death, ATP insufficiency, and susceptibility to genotoxic stress.

Immunometabolism – The Role of Branched-Chain Amino Acids

“…Consistent with the findings in terms of insulin resistance, the BCAA metabolism was also altered in various cancers (vide supra) (131)(132)(133)(134). In a seminal article, Sivanand and Heiden reviewed the fundamental perspectives concerning the critical role of BCAA metabolism in cancer (143).…”

“…Several recent works highlighted the importance of the BCAA metabolism and BCKDK in cancers (131)(132)(133)(134)(135)(136)(137). It was shown that higher BCKDK expression was associated with shorter survival in colorectal cancer, and BCKDK could promote tumorigenesis in vivo and ex vivo through the mitogen-activated protein kinase (MAPK) signaling pathway (131).…”

“…Another study documented that increased BCKDK expression was associated with metastasis in colorectal cancer ( 132 ). In addition, genetic and pharmacological inhibition of BCKDK sensitized tumor cells to cell death in triple-negative breast cancer (TNBC) cell lines ( 133 ). Additionally, another study revealed the relation between non-small cell lung cancer (NSCLC) and BCKDK.…”

Discovery of Proteins Responsible for Resistance to Three Chemotherapy Drugs in Breast Cancer Cells Using Proteomics and Bioinformatics Analysis

“…Recent studies have demonstrated that catabolism of BCAAs produces intermediates that are vital for driving triple-negative breast cancer (TNBC) growth and survival [ 38 ]. Moreover, BCAA catabolism dysregulation is significantly related to DR chemosensitivity and chemoresistance [ 39 ]. In addition, several upregulated proteins were involved in negative regulation of the p38-MAPK cascade.…”

Elevated BCAA Suppresses the Development and Metastasis of Breast Cancer

“…In TNBC, overexpressed SLC1A5, SLC7A5, and SLC6A14 promote glutamine metabolism and tumor growth ( 9 ). Promoting BCAA catabolism in TNBC suppresses protein translation, impairs mitochondrial function, and potentiates doxorubicin cytotoxicity ( 10 ). In addition to tumor growth, metabolic plasticity is also one important characteristic that distinguishes the tumor cells with high metastatic potentiality from non-metastatic tumor cells.…”