Caino, M. C. | Search bioRxiv

bioRxiv2022

NPC1 confers metabolic flexibility in Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) often undergoes at least partial epithelial-to-mesenchymal transition (EMT) to facilitate metastasis. Identifying EMT-associated characteristics can reveal novel dependencies that may serve as therapeutic vulnerabilities in this aggressive breast cancer subtype. We find that NPC1, which encodes the lysosomal cholesterol transporter Niemann-Pick Type C1 is highly expressed in TNBC as compared to estrogen receptor-positive (ER+) breast cancer and is significantly elevated in high grade disease. We demonstrate that NPC1 is directly targeted by microRNA-200c (miR-200c) a potent suppressor of EMT, providing a mechanism for its differential expression in breast cancer subtypes. Silencing of NPC1 in TNBC causes an accumulation of cholesterol-filled lysosomes and drives decreased growth on soft agar and invasive capacity. Conversely, overexpression of NPC1 in an ER+ cell line increases invasion and growth on soft agar. We further identify TNBC cell lines as cholesterol auxotrophs, however, they do not solely depend on NPC1 for adequate cholesterol supply. Genetic inhibition of NPC1 in TNBC cell lines led to altered mitochondrial function and morphology, suppression of mTOR signaling, and accumulation of autophagosomes. A small-molecule inhibitor of NPC1, U18666A, decreased TNBC proliferation and synergized with the chemotherapeutic drug, paclitaxel. This work suggests that NPC1 promotes aggressive characteristics in TNBC and identifies NPC1 as a potential therapeutic target.

cancer biology↗

bioRxiv2021

MIRO2 regulates prostate cancer cell growth via GCN1-dependent stress signaling

There is a continued need to identify novel therapeutic targets to prevent the mortality associated with prostate cancer. In this context, we discovered a novel mitochondrial signaling pathway that controls androgen-independent and androgen-sensitive prostate cancer cell growth. Mitochondrial Rho GTPase 2 (MIRO2) mRNA was upregulated in prostate cancer compared to localized tumors, and higher MIRO2 levels were correlated with poor patient survival. Using human cell lines that represent AR-independent or androgen-sensitive prostate cancer, we show that MIRO2 depletion impaired cell growth, colony formation and tumor growth in mice. Network analysis of MIRO2s binding partners identified metabolism, cell cycle, and cellular responses to extracellular stimuli amongst the top over-represented pathways. The top hit on our screen was General Control Non-derepressible 1 (GCN1). GCN1 was overexpressed in prostate cancer and MIRO2-GCN1 interacted in prostate cancer cell lines and in primary prostate cancer cells. Our results showed that MIRO2 is necessary for efficient GCN1-mediated GCN2 kinase activation and signaling, triggering translation of the transcription factor ATF4. Importantly, MIRO2 controlled ATF4 levels and transcriptional activity both in amino acid replete and depleted conditions. Furthermore, MIRO2s effect on regulating prostate cancer cell growth was partially mediated by ATF4. Finally, activation of GCN2 and ATF4 expression were correlated with MIRO2 expression in prostate cancer xenografts. Overall, we propose a new mechanism driving prostate cancer growth of both AR-independent and androgen-sensitive tumors.

cancer biology↗