A ligand-insensitive UNC5B splicing isoform regulates angiogenesis by promoting apoptosis

The Netrin-1 receptor UNC5B is an axon guidance regulator that is also expressed in endothelial cells (ECs), where it finely controls developmental and tumor angiogenesis. In the absence of Netrin-1, UNC5B induces apoptosis that is blocked upon Netrin-1 binding. Here, we identify an UNC5B splicing isoform (called UNC5B-Δ8) expressed exclusively by ECs and generated through exon skipping by NOVA2, an alternative splicing factor regulating vascular development. We show that UNC5B-Δ8 is a constitutively pro-apoptotic splicing isoform insensitive to Netrin-1 and required for specific blood vessel development in an apoptosis-dependent manner. Like NOVA2, UNC5B-Δ8 is aberrantly expressed in colon cancer vasculature where its expression correlates with tumor angiogenesis and poor patient outcome. Collectively, our data identify a mechanism controlling UNC5B’s necessary apoptotic function in ECs and suggest that the NOVA2/UNC5B circuit represents a post-transcriptional pathway regulating angiogenesis.

Glioblastoma invasion factor ODZ1 is induced by microenvironmental signals through activation of a Stat3-dependent transcriptional pathway

We have previously shown that the transmembrane protein ODZ1 serves for glioblastoma (GBM) cells to invade the surrounding tissue through activation of RhoA/ROCK pathway. However, the transcriptional machinery used by GBM cells to regulate the expression of ODZ1 is unknown. Here we show that interaction with tumor microenvironment elements, mainly activated monocytes through IL-6 secretion, and the extracellular matrix protein fibronectin, induces the Stat3 transcriptional pathway and upregulates ODZ1 which results in GBM cell migration. This signaling route is abrogated by blocking the IL-6 receptor, inhibiting Jak kinases or knocking down Stat3. Furthermore, we have identified a Stat3 responsive element in the ODZ1 gene promoter, about 1 kb from the transcription start site. Luciferase-reporter assays confirmed that the promoter responds to the presence of monocytic cells and this activation is greatly reduced when the Stat3 site is mutated or following treatment with a neutralizing anti-IL-6 receptor antibody or transfecting GBM cells with a dominant negative variant of Stat3. Overall, we show that monocyte-secreted IL-6 and the extracellular matrix protein fibronectin activate the axis Stat3-ODZ1 and promote migration of GBM cells. This is the first described transcriptional mechanism used by tumor cells to promote the expression of the invasion factor ODZ1.

The Oncogene Transcription Factor EB Regulates Vascular Functions

Transcription factor EB (TFEB) represents an emerging player in vascular biology. It belongs to the bHLH-leucine zipper transcription factor microphthalmia family, which includes microphthalmia-associated transcription factor, transcription factor E3 and transcription factor EC, and is known to be deregulated in cancer. The canonical transcriptional pathway orchestrated by TFEB adapts cells to stress in all kinds of tissues by supporting lysosomal and autophagosome biogenesis. However, emerging findings highlight that TFEB activates other genetic programs involved in cell proliferation, metabolism, inflammation and immunity. Here, we first summarize the general principles and mechanisms by which TFEB activates its transcriptional program. Then, we analyze the current knowledge of TFEB in the vascular system, placing particular emphasis on its regulatory role in angiogenesis and on the involvement of the vascular unit in inflammation and atherosclerosis.

Rimklb mutation causes male infertility in mice

Rimklb is a mammalian homologue of the E. coli enzyme RimK, which catalyzes addition of glutamic acid to the ribosomal protein S6. To date, no previous studies have shown any physiological role for Rimklb in mammals. In this study, using Western blotting, we found that Rimklb is distributed and expressed in mouse testis and heart. Rimklb was subsequently localized to the testicular Leydig cells using immunohistochemistry with an anti-Rimklb antibody. We generated a Rimklb mutant mouse in which a three-base deletion results in deletion of Ala 29 and substitution of Leu 30 with Val, which we named the RimklbA29del, L30V mutant mouse. RimklbA29del, L30V mutant mice show a decrease in testicular size and weight, and in vitro fertilization demonstrates complete male infertility. Furthermore, we found that a key factor in the mammalian target of the rapamycin/ribosomal protein S6 transcriptional pathway is hyperphosphorylated in the seminiferous tubules of the mutant testis. We conclude that Rimklb has important roles that include spermatogenesis in seminiferous tubules. In summary, male RimklbA29del, L30V mice are infertile.

Glioblastoma Invasion Factor ODZ1 is Induced by Microenvironmental Signals Through Activation of A Stat3-Dependent Transcriptional Pathway

We have previously shown that the transmembrane protein ODZ1 serves for glioblastoma (GBM) cells to invade the surrounding tissue through activation of RhoA/ROCK pathway. However, the transcriptional machinery used by GBM cells to regulate the expression of ODZ1 is unknown. Here we show that interaction with tumor microenvironment elements, mainly activated monocytes through IL-6 secretion, and the extracellular matrix protein fibronectin, induces the Stat3 transcriptional pathway and upregulates ODZ1 which results in GBM cell migration. This signaling route is abrogated by blocking the IL-6 receptor, inhibiting Jak kinases or knocking down Stat3. Furthermore, we have identified a Stat3 responsive element in the ODZ1 gene promoter, about 1 kb from the transcription start site. Luciferase-reporter assays confirmed that the promoter responds to the presence of monocytic cells and this activation is greatly reduced when the Stat3 site is mutated or following treatment with a neutralizing anti-IL-6 receptor antibody or transfecting GBM cells with a dominant negative variant of Stat3. Overall, we show that monocyte-secreted IL-6 and the extracellular matrix protein fibronectin activate the axis Stat3-ODZ1 and promote migration of GBM cells. This is the first described transcriptional mechanism used by tumor cells to promote the expression of the invasion factor ODZ1.

A double negative post-transcriptional regulatory circuit underlies the virgin behavioral state

The survival and reproductive success of animals depends on the ability to harmonize their external behaviors with their internal states. For example, females conduct numerous social programs that are distinctive to virgins, compared to post-mated and/or pregnant individuals. In Drosophila, the fact that this post-mating switch is initiated by seminal factors implies that the default state is virgin. However, we recently showed that loss of miR-iab-4/8-mediated repression of the transcription factor Homothorax (Hth) within the abdominal ventral nerve cord (VNC) causes virgin females to execute mated behaviors. To elucidate new components of this post-transcriptional regulatory circuit, we used genomic analysis of mir-iab-4/8 deletion and hth-miRNA binding site mutants (hth[BSmut]) to elucidate doublesex (dsx) as a critical downstream factor. While Dsx has mostly been studied during sex-specific differentiation, its activities in neurons are little known. We find that accumulation of Dsx in the CNS is highly complementary to Hth, and downregulated in miRNA/hth[BSmut] mutants. Moreover, virgin behavior is highly dose-sensitive to developmental dsx function. Strikingly, depletion of Dsx in SAG-1 cells, a highly restricted set of abdominal neurons, abrogates female virgin conducts in favor of mated behavioral programs. Thus, a double negative post-transcriptional pathway in the VNC (miR-iab-4/8 -| Hth -| Dsx) specifies the virgin behavioral state.