Greater Number of Microglia in Telencephalic Proliferative Zones of Human and Nonhuman Primate Compared with Other Vertebrate Species.

Microglial cells, the innate immune cells of the brain, are derived from yolk sac precursor cells, begin to colonize the telencephalon at the onset of cortical neurogenesis, and occupy specific layers including the telencephalic proliferative zones. Microglia are an intrinsic component of cortical germinal zones, establish extensive contacts with neural precursor cells (NPCs) and developing cortical vessels, and regulate the size of the NPC pool through mechanisms that include phagocytosis. Microglia exhibit notable differences in number and distribution in the prenatal neocortex between rat and old world nonhuman primate telencephalon, suggesting that microglia possess distinct properties across vertebrate species. To begin addressing this subject, we quantified the number of microglia and NPCs in proliferative zones of the fetal human, rhesus monkey, ferret, and rat, and the prehatch chick and turtle telencephalon. We show that the ratio of NPCs to microglia varies significantly across species. Few microglia populate the prehatch chick telencephalon, but the number of microglia approaches that of NPCs in fetal human and nonhuman primate telencephalon. These data demonstrate that microglia are in a position to perform important functions in a number of vertebrate species but more heavily colonize proliferative zones of fetal human and rhesus monkey telencephalon.

Fetal Rhesus Monkey First Trimester Zika Virus Infection Impacts Cortical Development in the Second and Third Trimesters.

Zika virus is a teratogen similar to other neurotropic viruses, notably cytomegalovirus and rubella. The goal of these studies was to address the direct impact of Zika virus on fetal development by inoculating early gestation fetal rhesus monkeys using an ultrasound-guided approach (intraperitoneal vs. intraventricular). Growth and development were monitored across gestation, maternal samples collected, and fetal tissues obtained in the second trimester or near term. Although normal growth and anatomical development were observed, significant morphologic changes were noted in the cerebral cortex at 3-weeks post-Zika virus inoculation including massive alterations in the distribution, density, number, and morphology of microglial cells in proliferative regions of the fetal cerebral cortex; an altered distribution of Tbr2+ neural precursor cells; increased diameter and volume of blood vessels in the cortical proliferative zones; and a thinner cortical plate. At 3-months postinoculation, alterations in morphology, distribution, and density of microglial cells were also observed with an increase in blood vessel volume; and a thinner cortical plate. Only transient maternal viremia was observed but sustained maternal immune activation was detected. Overall, these studies suggest persistent changes in cortical structure result from early gestation Zika virus exposure with durable effects on microglial cells.

Cortical Interlaminar Astrocytes Are Generated Prenatally, Mature Postnatally, and Express Unique Markers in Human and Nonhuman Primates.

Interlaminar astrocytes (ILAs) are a subset of cortical astrocytes that reside in layer I, express GFAP, have a soma contacting the pia, and contain long interlaminar processes that extend through several cortical layers. We studied the prenatal and postnatal development of ILAs in three species of primates (rhesus macaque, chimpanzee, and human). We found that ILAs are generated prenatally likely from radial glial (RG) cells, that ILAs proliferate locally during gestation, and that ILAs extend interlaminar processes during postnatal stages of development. We showed that the density and morphological complexity of ILAs increase with age, and that ILAs express multiple markers that are expressed by RG cells (Pax6, Sox2, and Nestin), specific to inner and outer RG cells (Cryab and Hopx), and astrocyte markers (S100ß, Aqp4, and GLAST) in prenatal stages and in adult. Finally, we demonstrated that rudimentary ILAs in mouse also express the RG markers Pax6, Sox2, and Nestin, but do not express S100ß, Cryab, or Hopx, and that the density and morphological complexity of ILAs differ between primate species and mouse. Together these findings contribute new information on astrogenesis of this unique class of cells and suggest a lineal relationship between RG cells and ILAs.

Development of the Neuro-Immune-Vascular Plexus in the Ventricular Zone of the Prenatal Rat Neocortex.

Microglial cells make extensive contacts with neural precursor cells (NPCs) and affiliate with vasculature in the developing cerebral cortex. But how vasculature contributes to cortical histogenesis is not yet fully understood. To better understand functional roles of developing vasculature in the embryonic rat cerebral cortex, we investigated the temporal and spatial relationships between vessels, microglia, and NPCs in the ventricular zone. Our results show that endothelial cells in developing cortical vessels extend numerous fine processes that directly contact mitotic NPCs and microglia; that these processes protrude from vessel walls and are distinct from tip cell processes; and that microglia, NPCs, and vessels are highly interconnected near the ventricle. These findings demonstrate the complex environment in which NPCs are embedded in cortical proliferative zones and suggest that developing vasculature represents a source of signaling with the potential to broadly influence cortical development. In summary, cortical histogenesis arises from the interplay among NPCs, microglia, and developing vasculature. Thus, factors that impinge on any single component have the potential to change the trajectory of cortical development and increase susceptibility for altered neurodevelopmental outcomes.

Role of miRNAs in tumor and endothelial cell interactions during tumor progression.

Cancer is a multistep disease based on crucial interactions between tumor cells and the microenvironment (extracellular matrix and stroma/immune cells). In fact, during dissemination, tumor cells have to escape from the primary tumor mass, cross the basal membrane, interact with endothelial cells to enter blood vessels (intravasation), survive in the bloodstream, get in contact with endothelial cells again to exit the bloodstream (extravasation) and seed in distant organs. Interactions between tumor and stroma cells are strongly coordinated by microRNAs (miRNAs), small non-coding RNAs able to silence protein coding genes by binding to specific recognition sites, mostly located at the 3' UTR of mature mRNAs. Relevantly, miRNA expression is often altered (overexpression or downregulation) in tumor cells and influenced by stroma cells. At the same time, miRNAs are abundant and essential in stroma cells during tumor cell dissemination and their expression is influenced by tumor cells. In fact, for instance, conditional ablation of Dicer in the endothelium of tumor bearing-mice leads to reduced tumor growth and microvessel density. In this review, we specifically focus on the role of miRNAs in endothelial cells regarding their positive or negative intervention on tumor angiogenesis or lymphoangiogenesis or when tumor cells detach from the tumor mass and intravasate or extravasate in/out of the blood vessels. Examples of pro-angiogenic miRNAs are miR-9 or miR-494, often overexpressed in tumors, which accumulate in tumor cell microvescicles and, therefore, get transferred to endothelial cells where they induce migration and angiogenesis. Differently, miR-200 and miR-128 are often downregulated in tumors and inhibit angiogenesis and lymphoangiogenesis. Instead, miR-126 controls intravasation while miR-146a, miR-214, miR-148b govern extravasation, in a positive or negative manner. Finally, at the end, we summarize opportunities for therapeutic interventions based on miRNAs acting on endothelial cells.

Periventricular microglial cells interact with dividing precursor cells in the nonhuman primate and rodent prenatal cerebral cortex.

Cortical proliferative zones have been studied for over 100 years, yet recent data have revealed that microglial cells constitute a sizeable proportion of ventricular zone cells during late stages of cortical neurogenesis. Microglia begin colonizing the forebrain after neural tube closure and during later stages of neurogenesis populate regions of the developing cortex that include the proliferative zones. We previously showed that microglia regulate the production of cortical cells by phagocytosing neural precursor cells (NPCs), but how microglia interact with NPCs remains poorly understood. Here we report on a distinct subset of microglial cells, which we term periventricular microglia, that are located near the lateral ventricle in the prenatal neocortex. Periventricular microglia exhibit a set of similar characteristics in embryonic rat and fetal rhesus monkey cortex. In both species, these cells occupy ~60 µm of the ventricular zone in the tangential axis and make contact with the soma and processes of NPCs dividing at the ventricle for over 50 µm along the radial axis. Periventricular microglia exhibit notable differences across species, including distinct morphological features such as terminal bouton-like structures that contact mitotic NPCs in the fetal rhesus monkey but not in rat. These morphological distinctions suggest differential functions of periventricular microglia in rat and rhesus monkey, yet are consistent with the concept that microglia regulate NPC function in the developing cerebral cortex of mammalian species.

Phosphatases control PKA-dependent functional microdomains at the outer mitochondrial membrane.

Evidence supporting the heterogeneity in cAMP and PKA signaling is rapidly accumulating and has been largely attributed to the localization or activity of adenylate cyclases, phosphodiesterases, and A-kinase-anchoring proteins in different cellular subcompartments. However, little attention has been paid to the possibility that, despite homogeneous cAMP levels, a major heterogeneity in cAMP/PKA signaling could be generated by the spatial distribution of the final terminators of this cascade, i.e., the phosphatases. Using FRET-based sensors to monitor cAMP and PKA-dependent phosphorylation in the cytosol and outer mitochondrial membrane (OMM) of primary rat cardiomyocytes, we demonstrate that comparable cAMP increases in these two compartments evoke higher levels of PKA-dependent phosphorylation in the OMM. This difference is most evident for small, physiological increases of cAMP levels and with both OMM-located probes and endogenous OMM proteins. We demonstrate that this disparity depends on differences in the rates of phosphatase-dependent dephosphorylation of PKA targets in the two compartments. Furthermore, we show that the activity of soluble phosphatases attenuates PKA-driven activation of the cAMP response element-binding protein while concurrently enhancing PKA-dependent mitochondrial elongation. We conclude that phosphatases can sculpt functionally distinct cAMP/PKA domains even in the absence of gradients or microdomains of this messenger. We present a model that accounts for these unexpected results in which the degree of PKA-dependent phosphorylation is dictated by both the subcellular distribution of the phosphatases and the different accessibility of membrane-bound and soluble phosphorylated substrates to the cytosolic enzymes.

Therapeutic Silencing of miR-214 Inhibits Tumor Progression in Multiple Mouse Models.

We previously demonstrated that miR-214 is upregulated in malignant melanomas and triple-negative breast tumors and promotes metastatic dissemination by affecting a complex pathway including the anti-metastatic miR-148b. Importantly, tumor dissemination could be reduced by blocking miR-214 function or increasing miR-148b expression or by simultaneous interventions. Based on this evidence, with the intent to explore the role of miR-214 as a target for therapy, we evaluated the capability of new chemically modified anti-miR-214, R97/R98, to inhibit miR-214 coordinated metastatic traits. Relevantly, when melanoma or breast cancer cells were transfected with R97/R98, anti-miR-214 reduced miR-214 expression and impaired transendothelial migration were observed. Noteworthy, when the same cells were injected in the tail vein of mice, cell extravasation and metastatic nodule formation in lungs were strongly reduced. Thus, suggesting that R97/R98 anti-miR-214 oligonucleotides were able to inhibit tumor cell escaping through the endothelium. More importantly, when R97/R98 anti-miR-214 compounds were systemically delivered to mice carrying melanomas or breast or neuroendocrine pancreatic cancers, a reduced number of circulating tumor cells and lung or lymph node metastasis formation were detected. Similar results were also obtained when AAV8-miR-214 sponges were used in neuroendocrine pancreatic tumors. Based on this evidence, we propose miR-214 as a promising target for anti-metastatic therapies.

The MCU complex in cell death.

During the 60s, the notion that positively charged Ca2+ ions are rapidly accumulated in energized mitochondria has been first established. In the following decades, mitochondrial Ca2+ homeostasis was shown to control cell metabolism, cell survival and other cell-specific functions through different mechanism. However, the molecular identity of the molecules controlling this process remained a mystery until just few years ago, when both mitochondrial Ca2+ uptake and release systems were genetically dissected. This finally opened the possibility to develop genetic model to directly test the contribution of mitochondrial Ca2+ homeostasis to cellular functions. Although the picture is still far from being clear, we here summarize and critically evaluate the current knowledge on how mitochondrial Ca2+ handling controls cell death.

miR-146a Exerts Differential Effects on Melanoma Growth and Metastatization.

UNLABELLED: Malignant melanoma is the most aggressive form of skin cancer; therefore, it is crucial to disclose its underlying molecular mechanisms. MicroRNAs (miRNAs) are small endogenous noncoding RNAs able to posttranscriptionally downregulate the expression of direct target genes. Using a melanoma progression model, miR-146a was identified as a key double-acting player in melanoma malignancy. In fact, miR-146a is able to enhance tumor growth, while it suppresses dissemination. It was determined that miR-146a coordinated melanoma cell growth by its direct targets lunatic fringe (LFNG) and NUMB, which operate on the NOTCH/PTEN/Akt pathway; while inhibition of metastasis formation was linked to decreased expression of ITGAV and ROCK1. Relevantly, miR-146a expression correlated with melanoma recurrence and was enriched in both patient-derived melanoma and cutaneous metastasis specimens, while its direct targets were depleted. However, miR-146a levels drop in circulating tumor cells (CTCs), suggesting the necessity for miR-146a expression to fluctuate during tumor progression in order to favor tumor growth and allow dissemination. This study reconciles the contradictory biologic functions of miR-146a in melanoma progression and unravels distinct molecular mechanisms that need to be considered for therapeutic interventions. IMPLICATIONS: miR-146a controls melanoma progression in a dual way, promoting growth and inhibiting dissemination; however, it is poorly expressed in CTCs, resulting in overall tumor spreading and distant-site colonization. Mol Cancer Res; 14(6); 548-62. ©2016 AACR.

miR-214 and miR-148b Targeting Inhibits Dissemination of Melanoma and Breast Cancer.

miR-214 and miR-148b have been proposed to antagonize the effects of each other in enabling or blocking metastasis, respectively. In this study, we provide evidence deepening their role and interrelationship in the process of metastatic dissemination. Depleting miR-214 or elevating miR-148b blocked the dissemination of melanoma or breast cancer cells, an effect that could be accentuated by dual alteration. Mechanistic investigations indicated that dual alteration suppressed passage of malignant cells through the blood vessel endothelium by reducing expression of the cell adhesion molecules ITGA5 and ALCAM. Notably, transendothelial migration in vitro and extravasation in vivo impaired by singly alternating miR-214 or miR-148b could be overridden by overexpression of ITGA5 or ALCAM in the same tumor cells. In clinical specimens of primary breast cancer or metastatic melanoma, we found a positive correlation between miR-214 and ITGA5 or ALCAM along with an inverse correlation of miR-214 and miR-148b in the same specimens. Our findings define an antagonistic relationship of miR-214 and miR-148b in determining the dissemination of cancer cells via tumor-endothelial cell interactions, with possible implications for microRNA-mediated therapeutic interventions aimed at blocking cancer extravasation. Cancer Res; 76(17); 5151-62. ©2016 AACR.

miR-214 as a key hub that controls cancer networks: small player, multiple functions.

MicroRNAs are short regulatory RNAs that are able to post-transcriptionally modulate gene expression and that have crucial roles in the control of physiological and pathological processes including cancer onset, growth, and progression. miR-214, located inside the sequence of the long noncoding Dmn3os transcript, contributes to the regulation of normal and cancer cell biology, even if it operates in a context-dependent and sometimes contradictory manner. miR-214 is deregulated in several human tumors including melanoma, breast, ovarian, gastric, and hepatocellular carcinomas. miR-214's pleiotropic and tumor-specific contribution to various cancer formation and progression hallmarks is achieved via its several target genes. In fact, miR-214 behaves as a key hub by coordinating fundamental signaling networks such as PTEN/AKT, ß-catenin, and tyrosine kinase receptor pathways. Interestingly, miR-214 also regulates the levels of crucial gene expression modulators: the epigenetic repressor Ezh2, "genome guardian" p53, transcription factors TFAP2, and another microRNA, miR-148b. Thus, miR-214 seems to have essential roles in coordinating tumor proliferation, stemness, angiogenesis, invasiveness, extravasation, metastasis, resistance to chemotherapy, and microenvironment. The sum of current literature reports suggests that miR-214 is a molecular hub involved in the control of cancer networks and, as such, could be a potential diagnostic/prognostic biomarker and target for therapeutic intervention.

miR-223 is a coordinator of breast cancer progression as revealed by bioinformatics predictions.

MicroRNAs are single-stranded non-coding RNAs that simultaneously down-modulate the expression of multiple genes post-transcriptionally by binding to the 3'UTRs of target mRNAs. Here we used computational methods to predict microRNAs relevant in breast cancer progression. Specifically, we applied different microRNA target prediction algorithms to various groups of differentially expressed protein-coding genes obtained from four breast cancer datasets. Six potential candidates were identified, among them miR-223, previously described to be highly expressed in the tumor microenvironment and known to be actively transferred into breast cancer cells. To investigate the function of miR-223 in tumorigenesis and to define its molecular mechanism, we overexpressed miR-223 in breast cancer cells in a transient or stable manner. Alternatively we overexpressed miR-223 in mouse embryonic fibroblasts or HEK293 cells and used their conditioned medium to treat tumor cells. With both approaches, we obtained elevated levels of miR-223 in tumor cells and observed decreased migration, increased cell death in anoikis conditions and augmented sensitivity to chemotherapy but no effect on adhesion and proliferation. The analysis of miR-223 predicted targets revealed enrichment in cell death and survival-related genes and in pathways frequently altered in breast cancer. Among these genes, we showed that protein levels for STAT5A, ITGA3 and NRAS were modulated by miR-223. In addition, we proved that STAT5A is a direct miR-223 target and highlighted a possible correlation between miR-223 and STAT5A in migration and chemotherapy response. Our investigation revealed that a computational analysis of cancer gene expression datasets can be a relevant tool to identify microRNAs involved in cancer progression and that miR-223 has a prominent role in breast malignancy that could potentially be exploited therapeutically.

miR-214 coordinates melanoma progression by upregulating ALCAM through TFAP2 and miR-148b downmodulation.

Malignant melanoma is one of the most aggressive human cancers, but the mechanisms governing its metastatic dissemination are not fully understood. Upregulation of miR-214 and ALCAM and the loss of TFAP2 expression have been implicated in this process, with TFAP2 a direct target of miR-214. Here, we link miR-214 and ALCAM as well as identify a core role for miR-214 in organizing melanoma metastasis. miR-214 upregulated ALCAM, acting transcriptionally through TFAP2 and also posttranscriptionally through miR-148b (itself controlled by TFAP2), both negative regulators of ALCAM. We also identified several miR-214-mediated prometastatic functions directly promoted by ALCAM. Silencing ALCAM in miR-214-overexpressing melanoma cells reduced cell migration and invasion without affecting growth or anoikis in vitro, and it also impaired extravasation and metastasis formation in vivo. Conversely, cell migration and extravasation was reduced in miR-214-overexpressing cells by upregulation of either miR-148b or TFAP2. These findings were consistent with patterns of expression of miR-214, ALCAM, and miR-148b in human melanoma specimens. Overall, our results define a pathway involving miR-214, miR-148b, TFAP2, and ALCAM that is critical for establishing distant metastases in melanoma.

miR148b is a major coordinator of breast cancer progression in a relapse-associated microRNA signature by targeting ITGA5, ROCK1, PIK3CA, NRAS, and CSF1.

Breast cancer is often fatal during its metastatic dissemination. To unravel the role of microRNAs (miRs) during malignancy, we analyzed miR expression in 77 primary breast carcinomas and identified 16 relapse-associated miRs that correlate with survival and/or distinguish tumor subtypes in different datasets. Among them, miR-148b, down-regulated in aggressive breast tumors, was found to be a major coordinator of malignancy. In fact, it is able to oppose various steps of tumor progression when overexpressed in cell lines by influencing invasion, survival to anoikis, extravasation, lung metastasis formation, and chemotherapy response. miR-148b controls malignancy by coordinating a novel pathway involving over 130 genes and, in particular, it directly targets players of the integrin signaling, such as ITGA5, ROCK1, PIK3CA/p110α, and NRAS, as well as CSF1, a growth factor for stroma cells. Our findings reveal the importance of the identified 16 miRs for disease outcome predictions and suggest a critical role for miR-148b in the control of breast cancer progression.

microRNA-214 contributes to melanoma tumour progression through suppression of TFAP2C.

Malignant melanoma is fatal in its metastatic stage. It is therefore essential to unravel the molecular mechanisms that govern disease progression to metastasis. MicroRNAs (miRs) are endogenous non-coding RNAs involved in tumourigenesis. Using a melanoma progression model, we identified a novel pathway controlled by miR-214 that coordinates metastatic capability. Pathway components include TFAP2C, homologue of a well-established melanoma tumour suppressor, the adhesion receptor ITGA3 and multiple surface molecules. Modulation of miR-214 influences in vitro tumour cell movement and survival to anoikis as well as extravasation from blood vessels and lung metastasis formation in vivo. Considering that miR-214 is known to be highly expressed in human melanomas, our data suggest a critical role for this miRNA in disease progression and the establishment of distant metastases.

AP-2alpha and AP-2gamma regulate tumor progression via specific genetic programs.

The events occurring during tumor formation and progression display similarities to some of the steps in embryonic morphogenesis. The family of AP-2 proteins consists of five different transcription factors (alpha, beta, gamma, delta, and epsilon) that play relevant roles in embryonic development, as demonstrated by the phenotypes of the corresponding knockout mice. Here, we show that AP-2alpha and AP-2gamma proteins play an essential role in tumorigenesis. Down-modulation of AP-2 expression in tumor cells by RNA interference (RNAi) led to enhanced tumor growth and reduced chemotherapy-induced cell death, as well as migration and invasion. Most of these biological modulations were rescued by AP-2 overexpression. We observed that increased xenotransplant growth was mostly due to highly enhanced proliferation of the tumor cells together with reduced innate immune cell recruitment. Moreover, we showed that migration impairment was mediated, at least in part, by secreted factors. To identify the genetic programs involved in tumorigenesis, we performed whole genome microarray analysis of AP-2alpha knockdown cells and observed that AP-2alpha regulates specific genes involved in cell cycle, cell death, adhesion, and migration. In particular, we showed that ESDN, EREG, and CXCL2 play a major role in AP-2 controlled migration, as ablation of any of these genes severely altered migration.

The AP-2alpha transcription factor regulates tumor cell migration and apoptosis.

AP-2 proteins are a family of developmentally-regulated transcription factors. They are encoded by five different genes (alpha, beta, gamma, delta, and epsilon) but they share a common structure. AP-2 plays relevant roles in growth, differentiation, and adhesion by controlling the transcription of specific genes. Evidence shows that the AP-2 genes are involved in tumorigenesis and for instance, they act as tumor suppressors in melanomas and mammary carcinomas. Here we investigated the function of the AP-2alpha protein in cancer formation and progression focusing on apoptosis and migration. We introduced AP-2alpha-specific siRNA (as oligos or in retroviruses) in HeLa or MCF-7 human tumor cells and obtained a pronounced down-modulation of AP-2a mRNA and protein levels. In these cells, we observed a significant reduction of chemotherapy-induced apoptosis, migration, and motility and an increase in adhesion suggesting a major role of AP-2a during cancer treatment and progression (migration and invasion). We have data suggesting that migration is, at least in part, regulated by secreted factors. By performing a whole genome microarray analysis of the tumor cells expressing AP-2alpha siRNA, we identified several AP-2alpha-regulated genes involved in apoptosis and migration such as FAST kinase, osteopontin, caspase 9, members of the TNF family, laminin alpha 1, collagen type XII, alpha 1, and adam.