Gain of HIF1 Activity and Loss of miRNA let-7d Promote Breast Cancer Metastasis to the Brain via the PDGF/PDGFR Axis

Abstract

Early detection and adjuvant therapies have significantly improved survival of patients with breast cancer over the past three decades. In contrast, management of metastatic disease remains unresolved. Brain metastasis is a late complication frequently observed among patients with metastatic breast cancer, whose poor prognosis calls for novel and more effective therapies. Here, we report that active hypoxia inducible factor-1 (HIF1) signaling and loss of the miRNA let-7d concur to promote brain metastasis in a recently established model of spontaneous breast cancer metastasis from the primary site to the brain (4T1-BM2), and additionally in murine and human experimental models of breast cancer brain metastasis (D2A1-BM2 and MDA231-BrM2). Active HIF1 and let-7d loss upregulated expression of platelet-derived growth factor (PDGF) B/A in murine and human brain metastatic cells, respectively, while either individual silencing of HIF1α and PDGF-A/B or let-7d overexpression suppressed brain metastasis formation in the tested models. Let-7d silencing upregulated HIF1α expression and HIF1 activity, indicating a regulatory hierarchy of the system. The clinical relevance of the identified targets was supported by human gene expression data analyses. Treatment of mice with nilotinib, a kinase inhibitor impinging on PDGF receptor (PDGFR) signaling, prevented formation of spontaneous brain metastases in the 4T1-BM2 model and reduced growth of established brain metastases in mouse and human models. These results identify active HIF1 signaling and let-7d loss as coordinated events promoting breast cancer brain metastasis through increased expression of PDGF-A/B. Moreover, they identify PDGFR inhibition as a potentially actionable therapeutic strategy for patients with brain metastatis. Significance: These findings show that loss of miRNA let-7d and active HIF1 signaling promotes breast cancer brain metastasis via PDGF and that pharmacologic inhibition of PDGFR suppresses brain metastasis, suggesting novel therapeutic opportunities.

The Role of microRNA Let-7d in Female Malignancies and Diseases of the Female Reproductive Tract

“…Dual-luciferase reporter assays confirmed that Jab1 was a direct regulatory target of let-7d, whereas in vitro assays on MDA-MB-231 and MCF-7 cells and xenograft in vivo assays demonstrated a role for let-7d in regulating breast cancer cell proliferation, invasion and tumor growth in vivo [ 57 ]. Let-7d was also shown to play a role in the development of breast cancer metastasis to the brain [ 62 ]. The loss of let-7d and activation of hypoxia-inducible factor-1 signaling induced brain metastasis via a platelet-derived growth factor (PDGF) pathway in a mouse model of spontaneous breast cancer metastasis from the primary site to the brain: If PDGFR was pharmacologically inhibited, experimental brain metastasis was suppressed, pointing out new therapeutic opportunities [ 62 ].…”

“…Let-7d was also shown to play a role in the development of breast cancer metastasis to the brain [ 62 ]. The loss of let-7d and activation of hypoxia-inducible factor-1 signaling induced brain metastasis via a platelet-derived growth factor (PDGF) pathway in a mouse model of spontaneous breast cancer metastasis from the primary site to the brain: If PDGFR was pharmacologically inhibited, experimental brain metastasis was suppressed, pointing out new therapeutic opportunities [ 62 ]. An example of another therapeutic approach is the analysis of microRNA as possible indicators of drug sensitivity.…”

Deciphering and Targeting Epigenetics in Cancer Metastasis

“…Breast cancer ncRNA lncRNA XIST EMT and MSN/c-Met [129] miR-10b - [130] miR-576-3p - [131] lncRNA BCBM lncRNA BCBM /JAK2/STAT3 [132] circBCBM1 circBCBM1/miR-125a/BRD4 axis [133] lncRNA-CCRR lncRNA-CCRR/connexin 43 [134] miRNA let-7d PDGF/PDGFR axis [135] miR-802-5p; miR-194-5p - [136] miR-132-3p; miR-199a-5p; miR-150-5p; miR-155-5p - [137] miR-211 SOX11/NGN2 axis [138] Notes: ESCC: esophageal squamous cell carcinoma; FSCN1: fascin actin-bundling protein 1; VDR: vitamin D receptor; KLF5: Kruppel like factor 5; bHLH transcription factor 2; CDK6: Cyclin Dependent Kinase-6; STAT3: signal transducer and activator of transcription-3; HDAC: histone deacetylase 1; ZEB1: Zinc Finger E-Box Binding Homeobox 1; ROCK1: Rho associated coiled-coil containing protein kinase 1; CRYAB: αB-crystallin; DNMTs: DNA methyltransferase; ERα: estrogen receptor alpha; TET2: ten-eleven translocation 2; IRX1: iroquois homeobox 1; PDK1: phosphoinositide-dependent kinase-1; ST7L: suppression of tumorigenicity 7 like; and BRD4: bromodomain containing 4.…”

“…By modulating connexin 43 expression, dysregulation of lncRNA-CCRR contributes to breast cancer brain metastases through intercellular coupling [134]. Loss of miRNA let-7d and active hypoxia-inducible factor-1 (HIF1) signaling enhances breast cancer brain metastasis via platelet-derived growth factor (PDGF), while pharmacologic inhibition of PDGF receptor (PDGFR) inhibits brain metastasis, implying new therapeutic possibilities [135]. miR-132-3p, miR-199a-5p, miR-150-5p, miR-155-5p, miR-802-5p and miR-194-5p from breast cancer cells also were identified the important role in brain metastasis [136,137].…”

Roles for growth factors and mutations in metastatic dissemination

“…• Loss of miRNA let-7d and gain of HIF1 activity promote breast cancer brain metastasis via PDGF; inhibition of PDGFR suppresses brain metastasis [119]. • In pericytes and stromal fibroblasts, the PDGF-BB-PDGFRβ-IL-33-ST2 axis recruits TAMs and induces metastasis [120].…”