Cerebral cavernous malformations (CCMs) are vascular malformations located within the central nervous system often resulting in cerebral hemorrhage. Pharmacological treatment is needed, since current therapy is limited to neurosurgery. Familial CCM is caused by loss‐of‐function mutations in any of Ccm1, Ccm2, and Ccm3 genes. CCM cavernomas are lined by endothelial cells (ECs) undergoing endothelial‐to‐mesenchymal transition (EndMT). This switch in phenotype is due to the activation of the transforming growth factor beta/bone morphogenetic protein (TGFβ/BMP) signaling. However, the mechanism linking Ccm gene inactivation and TGFβ/BMP‐dependent EndMT remains undefined. Here, we report that Ccm1 ablation leads to the activation of a MEKK3‐MEK5‐ERK5‐MEF2 signaling axis that induces a strong increase in Kruppel‐like factor 4 (KLF4) in ECs in vivo. KLF4 transcriptional activity is responsible for the EndMT occurring in CCM1‐null ECs. KLF4 promotes TGFβ/BMP signaling through the production of BMP6. Importantly, in endothelial‐specific Ccm1 and Klf4 double knockout mice, we observe a strong reduction in the development of CCM and mouse mortality. Our data unveil KLF4 as a therapeutic target for CCM. Synopsis Current therapy for cerebral cavernous malformation (CCM) therapy is limited to neurosurgery. Transcription factor KLF4 is found to be a crucial determinant for the development of cavernomas and thus a future therapeutic target. KLF4 is strongly upregulated in endothelial cells in the absence of any of the three CCM genes. The endothelial‐to‐mesenchymal transition observed in endothelial cells null for CCM1 is induced by KLF4. KLF4 activates TGFβ/BMP signaling by increasing Bmp6 expression in endothelial cells in the absence of CCM1. The development and progression of cavernomas is strongly reduced upon genetic Klf4 inactivation. KLF4 is a strong candidate as a novel target for the pharmacological treatment of CCM, since its inactivation reduces mouse mortality associated to this disease by 75%.

Significance: Cerebral cavernous malformation (CCM) disease can lead to brain hemorrhages, seizures, and paralysis. No pharmacological therapy is currently available. Here we define, to our knowledge for the first time in vivo, the sequence of molecular events that lead to CCM vascular cavernomas. We found that β-catenin activation is the first trigger followed by TGF-β signaling, which, in turn, mediates the progression of the disease. We also show that β-catenin signaling is cell-autonomous and independent of Wnt-receptor activation. Most importantly, these studies prompted us to identify pharmacological agents that, by targeting the altered β-catenin signaling, limit the formation of brain vascular cavernomas in mice with CCM3 ablation in endothelial cells. These drugs are currently used in clinics for different pathologies and may be repurposed for CCM therapy.

Background and Purpose—: Cerebral cavernous malformation (CCM) is characterized by multiple lumen vascular malformations in the central nervous system that can cause neurological symptoms and brain hemorrhages. About 20% of CCM patients have an inherited form of the disease with ubiquitous loss-of-function mutation in any one of 3 genes CCM1 , CCM2 , and CCM3 . The rest of patients develop sporadic vascular lesions histologically similar to those of the inherited form and likely mediated by a biallelic acquired mutation of CCM genes in the brain vasculature. However, the molecular phenotypic features of endothelial cells in CCM lesions in sporadic patients are still poorly described. This information is crucial for a targeted therapy. Methods—: We used immunofluorescence microscopy and immunohistochemistry to analyze the expression of endothelial-to-mesenchymal transition markers in the cavernoma of sporadic CCM patients in parallel with human familial cavernoma as a reference control. Results—: We report here that endothelial cells, a cell type critically involved in CCM development, undergo endothelial-to-mesenchymal transition in the lesions of sporadic patients. This switch in endothelial phenotype has been described only in genetic CCM patients and in murine models of the disease. In addition, TGF-β/p-Smad- and β-catenin-dependent signaling pathways seem activated in sporadic cavernomas as in familial ones. Conclusions—: Our findings support the use of common therapeutic strategies for both sporadic and genetic CCM malformations.

Elucidating the molecular basis of tumor metastasis is pivotal for eradicating cancer-related mortality. Triple-negative breast cancer (TNBC) encompasses a class of aggressive tumors characterized by high rates of recurrence and metastasis, as well as poor overall survival. Here, we find that the promyelocytic leukemia protein PML exerts a prometastatic function in TNBC that can be targeted by arsenic trioxide. We found that, in TNBC patients, constitutive HIF1A activity induces high expression of PML, along with a number of HIF1A target genes that promote metastasis at multiple levels. Intriguingly, PML controls the expression of these genes by binding to their regulatory regions along with HIF1A. This mechanism is specific to TNBC cells and does not occur in other subtypes of breast cancer where PML and prometastatic HIF1A target genes are underexpressed. As a consequence, PML promotes cell migration, invasion, and metastasis in TNBC cell and mouse models. Notably, pharmacological inhibition of PML with arsenic trioxide, a PML-degrading agent used to treat promyelocytic leukemia patients, delays tumor growth, impairs TNBC metastasis, and cooperates with chemotherapy by preventing metastatic dissemination. In conclusion, we report identification of a prometastatic pathway in TNBC and suggest clinical development toward the use of arsenic trioxide for TNBC patients.

Acute promyelocytic leukemia (APL) is epitomized by the chromosomal translocation t(15;17) and the resulting oncogenic fusion protein PML‐RARα. Although acting primarily as a transcriptional repressor, PML‐RARα can also exert functions of transcriptional co‐activation. Here, we find that PML‐RARα stimulates transcription driven by HIF factors, which are critical regulators of adaptive responses to hypoxia and stem cell maintenance. Consistently, HIF‐related gene signatures are upregulated in leukemic promyelocytes from APL patients compared to normal promyelocytes. Through in vitro and in vivo studies, we find that PML‐RARα exploits a number of HIF‐1α‐regulated pro‐leukemogenic functions that include cell migration, bone marrow (BM) neo‐angiogenesis and self‐renewal of APL blasts. Furthermore, HIF‐1α levels increase upon treatment of APL cells with all‐ trans retinoic acid (ATRA). As a consequence, inhibiting HIF‐1α in APL mouse models delays leukemia progression and exquisitely synergizes with ATRA to eliminate leukemia‐initiating cells (LICs).