Human endogenous retrovirus onco-exaptation counters cancer cell senescence through calbindin.

Increased levels and diversity of human endogenous retrovirus (HERV) transcription characterize most cancer types and are linked with disease outcomes. However, the underlying processes are incompletely understood. Here, we show that elevated transcription of HERVH proviruses predicted survival of lung squamous cell carcinoma (LUSC) and identified an isoform of CALB1, encoding calbindin, ectopically driven by an upstream HERVH provirus under the control of KLF5, as the mediator of this effect. HERVH-CALB1 expression was initiated in preinvasive lesions and associated with their progression. Calbindin loss in LUSC cell lines impaired in vitro and in vivo growth and triggered senescence, consistent with a protumor effect. However, calbindin also directly controlled the senescence-associated secretory phenotype (SASP), marked by secretion of CXCL8 and other neutrophil chemoattractants. In established carcinomas, CALB1-negative cancer cells became the dominant source of CXCL8, correlating with neutrophil infiltration and worse prognosis. Thus, HERVH-CALB1 expression in LUSC may display antagonistic pleiotropy, whereby the benefits of escaping senescence early during cancer initiation and clonal competition were offset by the prevention of SASP and protumor inflammation at later stages.

E3 ubiquitin ligase HECTD2 mediates melanoma progression and immune evasion.

The ubiquitin-proteasome system maintains protein homoeostasis, underpins the cell cycle, and is dysregulated in cancer. However, the role of individual E3 ubiquitin ligases, which mediate the final step in ubiquitin-mediated proteolysis, remains incompletely understood. Identified through screening for cancer-specific endogenous retroviral transcripts, we show that the little-studied E3 ubiquitin ligase HECTD2 exerts dominant control of tumour progression in melanoma. HECTD2 cell autonomously drives the proliferation of human and murine melanoma cells by accelerating the cell cycle. HECTD2 additionally regulates cancer cell production of immune mediators, initiating multiple immune suppressive pathways, which include the cyclooxygenase 2 (COX2) pathway. Accordingly, higher HECTD2 expression is associated with weaker anti-tumour immunity and unfavourable outcome of PD-1 blockade in human melanoma and counteracts immunity against a model tumour antigen in murine melanoma. This central, multifaceted role of HECTD2 in cancer cell-autonomous proliferation and in immune evasion may provide a single target for a multipronged therapy of melanoma.

STAT3 labels a subpopulation of reactive astrocytes required for brain metastasis.

The brain microenvironment imposes a particularly intense selective pressure on metastasis-initiating cells, but successful metastases bypass this control through mechanisms that are poorly understood. Reactive astrocytes are key components of this microenvironment that confine brain metastasis without infiltrating the lesion. Here, we describe that brain metastatic cells induce and maintain the co-option of a pro-metastatic program driven by signal transducer and activator of transcription 3 (STAT3) in a subpopulation of reactive astrocytes surrounding metastatic lesions. These reactive astrocytes benefit metastatic cells by their modulatory effect on the innate and acquired immune system. In patients, active STAT3 in reactive astrocytes correlates with reduced survival from diagnosis of intracranial metastases. Blocking STAT3 signaling in reactive astrocytes reduces experimental brain metastasis from different primary tumor sources, even at advanced stages of colonization. We also show that a safe and orally bioavailable treatment that inhibits STAT3 exhibits significant antitumor effects in patients with advanced systemic disease that included brain metastasis. Responses to this therapy were notable in the central nervous system, where several complete responses were achieved. Given that brain metastasis causes substantial morbidity and mortality, our results identify a novel treatment for increasing survival in patients with secondary brain tumors.

Author Correction: STAT3 labels a subpopulation of reactive astrocytes required for brain metastasis.

In the version of this article originally published, the names of three authors were incorrect. The authors were listed as "Coral Fustero-Torres", "Elena Pineiro" and "Melchor Sánchez-Martínez". Their respective names are "Coral Fustero-Torre", "Elena Piñeiro-Yáñez" and "Melchor Sanchez-Martinez". The errors have been corrected in the print, HTML and PDF versions of this article.

Kidins220/ARMS modulates the activity of microtubule-regulating proteins and controls neuronal polarity and development.

In order for neurons to perform their function, they must establish a highly polarized morphology characterized, in most of the cases, by a single axon and multiple dendrites. Herein we find that the evolutionarily conserved protein Kidins220 (kinase D-interacting substrate of 220-kDa), also known as ARMS (ankyrin repeat-rich membrane spanning), a downstream effector of protein kinase D and neurotrophin and ephrin receptors, regulates the establishment of neuronal polarity and development of dendrites. Kidins220/ARMS gain and loss of function experiments render severe phenotypic changes in the processes extended by hippocampal neurons in culture. Although Kidins220/ARMS early overexpression hinders neuronal development, its down-regulation by RNA interference results in the appearance of multiple longer axon-like extensions as well as aberrant dendritic arbors. We also find that Kidins220/ARMS interacts with tubulin and microtubule-regulating molecules whose role in neuronal morphogenesis is well established (microtubule-associated proteins 1b, 1a, and 2 and two members of the stathmin family). Importantly, neurons where Kidins220/ARMS has been knocked down register changes in the phosphorylation activity of MAP1b and stathmins. Altogether, our results indicate that Kidins220/ARMS is a key modulator of the activity of microtubule-regulating proteins known to actively regulate neuronal morphogenesis and suggest a mechanism by which it contributes to control neuronal development.

Vaccinia-virus-induced cellular contractility facilitates the subcellular localization of the viral replication sites.

Poxviruses, such as vaccinia virus (VV), replicate their DNA in endoplasmic-reticulum-enclosed cytoplasmic sites. Here, we compare the dynamics of the VV replication sites with those of the attenuated strain, modified VV Ankara (MVA). By live-cell imaging, small, early replication sites of both viruses undergo motility typical of microtubule (MT)-motor-mediated movement. Over time, growing replication sites of VV collect around the nucleus in a MT-dependent fashion, whereas those of MVA remain mostly scattered in the cytoplasm. Surprisingly, blocking the dynein function does not impair the perinuclear accumulation of large VV replication sites. Live-cell imaging demonstrates that in contrast to small replication sites, large sites do not display MT-motor-mediated motility. Instead, VV infection induces cellular contractility that facilitates the collection of growing replication sites around the nucleus. In a subset of cells (30-40%), this VV-induced contractility is alternated by phases of directed cell migration, suggesting that the two processes may be linked. The MVA-infected cells do not display contractility or cell migration, supporting the idea that these cellular activities facilitate the efficient accumulation of the VV replication sites around the nucleus. We propose that the recently described cytoskeletal rearrangements induced by VV are a prerequisite for the observed cell contractility and migration activities that apparently contribute to the organization of the complex cytoplasmic life cycle of VV.

Relationship between vaccinia virus intracellular cores, early mRNAs, and DNA replication sites.

Virus assembly, a late event in the life cycle of vaccinia virus (VV), is preceded by a number of steps that all occur in the cytoplasm of the infected host cell: virion entry, delivery of the viral core into the cytoplasm, and transcription from these cores of early mRNAs, followed by the process of DNA replication. In the present study the quantitative and structural relationships between these distinct steps of VV morphogenesis were investigated. We show that viral RNA and DNA synthesis increases linearly with increasing amounts of incoming cores. Moreover, at multiplicities of infection that result in 10 to 40 cores per cell, an approximately 1:1 ratio between cores and sites of DNA replication exists, suggesting that each core is infectious. We have shown previously that VV early mRNAs collect in distinct granular structures that recruit components of the host cell translation machinery. Strikingly, these structures appeared to form some distance away from intracellular cores (M. Mallardo, S. Schleich, and J. Krijnse Locker, Mol. Biol. Cell 12:3875-3891, 2001). In the present study the intracellular locations of the sites of early mRNA accumulation and those of the subsequent process of DNA replication were compared. We show that these are distinct structures that have different intracellular locations. Finally, we study the fate of the parental DNA after core uncoating. By electron microscopy, cores were found close to membranes of the endoplasmic reticulum (ER) and the parental DNA, once it had left the core, appeared to associate preferentially with the cytosolic side of those membranes. Since we have previously shown that the process of DNA replication occurs in an ER-enclosed cytosolic "subcompartment" (N. Tolonen, L. Doglio, S. Schleich, and J. Krijnse Locker, Mol. Biol. Cell 12:2031-2046, 2001), the present data suggest that the parental DNA is released into the cytosol and associates with the same membranes where DNA replication is subsequently initiated. The combined data are discussed with respect to the cytosolic organization of VV morphogenesis.