Kynurenine 3-monooxygenase upregulates pluripotent genes through β-catenin and promotes triple-negative breast cancer progression

Abstract

Background: Triple-negative breast cancer (TNBC) is aggressive and has a poor prognosis. Kynurenine 3-monooxygenase (KMO), a crucial kynurenine metabolic enzyme, is involved in inflammation, immune response and tumorigenesis. We aimed to study the role of KMO in TNBC. Methods: KMO alteration and expression data from public databases were analyzed. KMO expression levels in TNBC samples were analyzed using immunohistochemistry. Knockdown of KMO in TNBC cells was achieved by RNAi and CRISPR/Cas9. KMO functions were examined by MTT, colony-forming, transwell migration/invasion, and mammosphere assays. The molecular events were analyzed by cDNA microarrays, Western blot, quantitative real-time PCR and luciferase reporter assays. Tumor growth and metastasis were detected by orthotopic xenograft and tail vein metastasis mouse models, respectively. Findings: KMO was amplified and associated with worse survival in breast cancer patients. KMO expression levels were higher in TNBC tumors compared to adjacent normal mammary tissues. In vitro ectopic KMO expression increased cell growth, colony and mammosphere formation, migration, invasion as well as mesenchymal marker expression levels in TNBC cells. In addition, KMO increased pluripotent gene expression levels and promoter activities in vitro. Mechanistically, KMO was associated with b-catenin and prevented b-catenin degradation, thereby enhancing the transcription of pluripotent genes. KMO knockdown suppressed tumor growth and the expression levels of b-catenin, CD44 and Nanog. Furthermore, mutant KMO (known with suppressed enzymatic activity) could still promote TNBC cell migration/invasion. Importantly, mice bearing CRISPR KMO-knockdown TNBC tumors showed decreased lung metastasis and prolonged survival. Interpretation: KMO regulates pluripotent genes via b-catenin and plays an oncogenic role in TNBC progression.

Significance of Kynurenine 3-Monooxygenase Expression in Colorectal Cancer

“…KMO is an outer mitochondrial membrane enzyme that controls kynurenine catabolism. KMO inhibitors, which suppress KMO activity (16), were used to address the role of KMO activity in CRC progression. Inhibition of KMO with UPF 648 did not affect the OCR or basal ECAR of CRC cells (Supplementary Figure 4).…”

“…KMO serves as a therapeutic target in multiple-organ failure, systemic inflammatory response, Huntington's disease, and immune adaptive response (13,14). Recently, upregulation of KMO in hepatocellular carcinoma and triple-negative breast cancer tissues has been reported (15,16). These studies suggest that KMO participates in cancer progression, whereas the role of KMO in CRC tumorigenesis and aggressiveness has not yet been demonstrated.…”

Kynurenine Monooxygenase Expression and Activity in Human Astrocytomas

“…There are three main hypotheses with regard to the relevance of active tryptophan catabolism through the KP in the tumor microenvironment [59]: first, overexpression of active IDO from malignant cells may deplete the tryptophan pool, thus inhibiting lymphocyte proliferation and abrogating the anti-tumor immune response [34]; second, active KP metabolism could favor the formation of tryptophan derivates that inhibit the proliferation of cytotoxic lymphocytes and induce their death [35,36]; and third, the KP can lead to the constant formation of NAD + , a coenzyme involved in metabolic and signaling pathways, contributing to the suitability of malignant cells [60]. In accordance with this, KMO is the pivotal enzyme in the KP that leads to NAD + synthesis [61] and is related to poor prognosis in several cancers [58,[62][63][64].…”

“…In this study, KMO mRNA expression did not affect patient survival, which could be due to the population size. However, KMO overexpression is related to malignancy and poor prognosis in patients with triple-negative breast cancer and colorectal cancer [58,62]. Furthermore, the oncogenic activity of KMO favors the potentiation of β-catenin signaling in an enzymeactivity-independent manner, indicating the role of KMO beyond 3-HK production [62].…”

“…However, KMO overexpression is related to malignancy and poor prognosis in patients with triple-negative breast cancer and colorectal cancer [58,62]. Furthermore, the oncogenic activity of KMO favors the potentiation of β-catenin signaling in an enzymeactivity-independent manner, indicating the role of KMO beyond 3-HK production [62]. KMO overexpression is also related to malignancy and poor prognosis in canine mammary gland tumors and melanomas.…”