SUMMARY Mapping host-pathogen interactions has proven instrumental for understanding how viruses manipulate host machinery and how numerous cellular processes are regulated. DNA viruses such as herpesviruses have relatively large coding capacity and thus can target an extensive network of cellular proteins. To identify the host proteins hijacked by this pathogen, we systematically affinity tagged and purified all 89 proteins of Kaposi’s sarcoma-associated herpesvirus (KSHV) from human cells. Mass spectrometry of this material identified over 500 virus-host interactions. KSHV causes AIDS-associated cancers and its interaction network is enriched for proteins linked to cancer and overlaps with proteins that are also targeted by HIV-1. We found that the conserved KSHV protein ORF24 binds to RNA polymerase II and brings it to viral late promoters by mimicking and replacing cellular TATA-box-binding protein (TBP). This is required for herpesviral late gene expression, a complex and poorly understood phase of the viral lifecycle.
Brain metastasis is a significant cause of morbidity and mortality in multiple cancer types and represents an unmet clinical need. The mechanisms that mediate metastatic cancer growth in the brain parenchyma are largely unknown. Melanoma, which has the highest rate of brain metastasis among common cancer types, is an ideal model to study how cancer cells adapt to the brain parenchyma. Our unbiased proteomics analysis of melanoma short-term cultures revealed that proteins implicated in neurodegenerative pathologies are differentially expressed in melanoma cells explanted from brain metastases compared to those derived from extracranial metastases. We showed that melanoma cells require amyloid beta (AB) for growth and survival in the brain parenchyma. Melanoma-secreted AB activates surrounding astrocytes to a pro-metastatic, anti-inflammatory phenotype and prevents phagocytosis of melanoma by microglia. Finally, we demonstrate that pharmacological inhibition of AB decreases brain metastatic burden.
26Brain metastasis is a significant cause of morbidity and mortality in multiple cancer 27 types and represents an unmet clinical need. The mechanisms that mediate metastatic 28 cancer growth in the brain parenchyma are largely unknown. Melanoma, which has the 29 highest rate of brain metastasis among common cancer types, is an ideal model to 30 study how cancer cells adapt to the brain parenchyma. We performed unbiased 31 proteomics analysis of melanoma short-term cultures, a novel model for the study of 32 brain metastasis. Intriguingly, we found that proteins implicated in neurodegenerative 33 pathologies are differentially expressed in melanoma cells explanted from brain 34 metastases compared to those derived from extracranial metastases. This raised the 35 exciting hypothesis that molecular pathways implicated in neurodegenerative disorders 36 are critical for metastatic adaptation to the brain. 37 38Here, we show that melanoma cells require amyloid beta (Ab), a polypeptide heavily 39 implicated in Alzheimer's disease, for growth and survival in the brain parenchyma. 40Melanoma cells produce and secrete Ab, which activates surrounding astrocytes to a 41 pro-metastatic, anti-inflammatory phenotype. Furthermore, we show that 42 pharmacological inhibition of Ab decreases brain metastatic burden. 43 44Our results reveal a mechanistic connection between brain metastasis and Alzheimer's 45 disease -two previously unrelated pathologies, establish Ab as a promising therapeutic 46 target for brain metastasis, and demonstrate suppression of neuroinflammation as a 47 critical feature of metastatic adaptation to the brain parenchyma. 48 49 3 Main 50 51Brain metastasis is the most common form of adult intracranial malignancy 1 and results 52 in severe morbidity and mortality. 40-75% of Stage IV melanoma patients develop brain 53 metastasis 2,3 , reflecting melanoma's striking ability to colonize the brain. Brain 54 metastases are less responsive than extracranial metastases to current cancer 55 therapies 4-6 , and the majority of patients succumb to disease in less than one year 7 . 56 Furthermore, patients with brain metastasis are often excluded from clinical trials and 57 urgently need new clinical options. In recent years, research has started to elucidate the 58 molecular mechanisms contributing to the multi-step process of brain metastasis. Most 59 findings have focused on cancer extravasation across the blood-brain barrier (BBB), 60 which cannot be leveraged therapeutically given that the vast majority of brain 61 metastasis patients will present with extravasated cancer cells at the time of cancer 62 diagnosis. The main bottleneck in the brain metastatic process has been shown to be 63 the successful expansion of a single cell in the brain parenchyma to form a macro-64 metastasis 8 . Recent studies have begun to demonstrate the role of the brain 65 microenvironment in this process. In particular, reactive astrocytes have been shown to 66 interact with cancer cells in the brain 9,10 and exhibit both pro-and anti-...
MicroRNAs (miRNAs) are a class of endogenous non-coding small RNAs that post-transcriptionally control the translation and stability of target mRNAs in a sequence-dependent manner. MiRNAs are essential for key cellular processes including proliferation, differentiation, cell death and metabolism, among others. Consequently, alterations of miRNA expression contribute to developmental defects and a myriad of diseases.The expression of miRNAs can be altered by several mechanisms including gene copy number alterations, aberrant DNA methylation, defects of the miRNA processing machinery or unscheduled expression of transcription factors. In this work, we sought to analyze the regulation of the miR-182 cluster, located at the 7q32 locus, which encodes three different miRNAs that are abundantly expressed in human embryonic stem cells and de-regulated in cancer. We have found that the Krüppel-like factor 4 (KLF4) directly regulates miR-182 cluster expression in human embryonic stem cells (hESCs) and in melanoma tumors, in which the miR-182 cluster is highly expressed and has a pro-metastatic role. Furthermore, higher KLF4 expression was found to be associated with metastatic progression and poor patient outcome. Loss of function experiments revealed that KLF4 is required for melanoma cell maintenance. These findings provide new insights into the regulation of the miR-182 cluster expression and new opportunities for therapeutic intervention in tumors in which the KLF4-miR-182 cluster axis is deregulated.
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