Toll-9 interacts with Toll-1 to mediate a feedback loop during apoptosis-induced proliferation in Drosophila.

Drosophila Toll-1 and all mammalian Toll-like receptors regulate innate immunity. However, the functions of the remaining eight Toll-related proteins in Drosophila are not fully understood. Here, we show that Drosophila Toll-9 is necessary and sufficient for a special form of compensatory proliferation after apoptotic cell loss (undead apoptosis-induced proliferation [AiP]). Mechanistically, for AiP, Toll-9 interacts with Toll-1 to activate the intracellular Toll-1 pathway for nuclear translocation of the NF-κB-like transcription factor Dorsal, which induces expression of the pro-apoptotic genes reaper and hid. This activity contributes to the feedback amplification loop that operates in undead cells. Given that Toll-9 also functions in loser cells during cell competition, we define a general role of Toll-9 in cellular stress situations leading to the expression of pro-apoptotic genes that trigger apoptosis and apoptosis-induced processes such as AiP. This work identifies conceptual similarities between cell competition and AiP.

Oncogenic Pathways and Loss of the Rab11 GTPase Synergize To Alter Metabolism in Drosophila.

Colorectal cancer is a complex disease driven by well-established mutations such as APC and other yet to be identified pathways. The GTPase Rab11 regulates endosomal protein trafficking, and previously we showed that loss of Rab11 caused intestinal inflammation and hyperplasia in mice and flies. To test the idea that loss of Rab11 may promote cancer progression, we have analyzed archival human patient tissues and observed that 51 out of 70 colon cancer tissues had lower Rab11 protein staining. By using the Drosophila midgut model, we have found that loss of Rab11 can lead to three changes that may relate to cancer progression. First is the disruption of enterocyte polarity based on staining of the FERM domain protein Coracle. Second is an increased proliferation due to an increased expression of the JAK-STAT pathway ligand Upd3. Third is an increased expression of ImpL2, which is an IGFBP7 homolog and can suppress metabolism. Furthermore, loss of Rab11 can act synergistically with the oncoprotein RasV12 to regulate these cancer-related phenotypes.

Recycling Endosomes in Mature Epithelia Restrain Tumorigenic Signaling.

The effects of polarized membrane trafficking in mature epithelial tissue on cell growth and cancer progression have not been fully explored in vivo. A majority of colorectal cancers have reduced and mislocalized Rab11, a small GTPase dedicated to trafficking of recycling endosomes. Patients with low Rab11 protein expression have poor survival rates. Using genetic models across species, we show that intact recycling endosome function restrains aberrant epithelial growth elicited by APC or RAS mutations. Loss of Rab11 protein led to epithelial dysplasia in early animal development and synergized with oncogenic pathways to accelerate tumor progression initiated by carcinogen, genetic mutation, or aging. Transcriptomic analysis uncovered an immediate expansion of the intestinal stem cell pool along with cell-autonomous Yki/Yap activation following disruption of Rab11a-mediated recycling endosomes. Intestinal tumors lacking Rab11a traffic exhibited marked elevation of nuclear Yap, upd3/IL6-Stat3, and amphiregulin-MAPK signaling, whereas suppression of Yki/Yap or upd3/IL6 reduced gut epithelial dysplasia and hyperplasia. Examination of Rab11a function in enteroids or cultured cell lines suggested that this endosome unit is required for suppression of the Yap pathway by Hippo kinases. Thus, recycling endosomes in mature epithelia constitute key tumor suppressors, loss of which accelerates carcinogenesis. SIGNIFICANCE: Recycling endosome traffic in mature epithelia constitutes a novel tumor suppressing mechanism.

The Misshapen subfamily of Ste20 kinases regulate proliferation in the aging mammalian intestinal epithelium.

The intestinal epithelium has a high rate of cell turn over and is an excellent system to study stem cell-mediated tissue homeostasis. The Misshapen subfamily of the Ste20 kinases in mammals consists of misshapen like kinase 1 (MINK1), mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4), and TRAF2 and NCK interacting kinase (TNIK). Recent reports suggest that this subfamily has a novel function equal to the Hippo/MST subfamily as upstream kinases for Warts/Large tumor suppressor kinase (LATS) to suppress tissue growth. To study the in vivo functions of Mink1, Map4k4, and Tnik, we generated a compound knockout of these three genes in the mouse intestinal epithelium. The intestinal epithelia of the mutant animals were phenotypically normal up to approximately 12 months. The older animals then exhibited mildly increased proliferation throughout the lower GI tract. We also observed that the normally spatially organized Paneth cells in the crypt base became dispersed. The expression of one of the YAP pathway target genes Sox9 was increased while other target genes including CTGF did not show a significant change. Therefore, the Misshapen and Hippo subfamilies may have highly redundant functions to regulate growth in the intestinal epithelium, as illustrated in recent tissue culture models.

Ingestion of Food Particles Regulates the Mechanosensing Misshapen-Yorkie Pathway in Drosophila Intestinal Growth.

The intestinal epithelium has a high cell turnover rate and is an excellent system to study stem cell-mediated adaptive growth. In the Drosophila midgut, the Ste20 kinase Misshapen, which is distally related to Hippo, has a niche function to restrict intestinal stem cell activity. We show here that, under low growth conditions, Misshapen is localized near the cytoplasmic membrane, is phosphorylated at the threonine 194 by the upstream kinase Tao, and is more active toward Warts, which in turn inhibits Yorkie. Ingestion of yeast particles causes a midgut distention and a reduction of Misshapen membrane association and activity. Moreover, Misshapen phosphorylation is regulated by the stiffness of cell culture substrate, changing of actin cytoskeleton, and ingestion of inert particles. These results together suggest that dynamic membrane association and Tao phosphorylation of Misshapen are steps that link the mechanosensing of intestinal stretching after food particle ingestion to control adaptive growth.

Autographa californica Nucleopolyhedrovirus AC141 (Exon0), a Potential E3 Ubiquitin Ligase, Interacts with Viral Ubiquitin and AC66 To Facilitate Nucleocapsid Egress.

During the infection cycle of Autographa californica multiple nucleopolyhedrovirus (AcMNPV), two forms of virions are produced, budded virus (BV) and occlusion-derived virus (ODV). Nucleocapsids that form BV have to egress from the nucleus, whereas nucleocapsids that form ODV remain inside the nucleus. The molecular mechanism that determines whether nucleocapsids remain inside or egress from the nucleus is unknown. AC141 (a predicted E3 ubiquitin ligase) and viral ubiquitin (vUbi) have both been shown to be required for efficient BV production. In this study, it was hypothesized that vUbi interacts with AC141, and in addition, that this interaction was required for BV production. Deletion of both ac141 and vubi restricted viral infection to a single cell, and BV production was completely eliminated. AC141 was ubiquitinated by either vUbi or cellular Ubi, and this interaction was required for optimal BV production. Nucleocapsids in BV, but not ODV, were shown to be specifically ubiquitinated by vUbi, including a 100-kDa protein, as well as high-molecular-weight conjugates. The viral ubiquitinated 100-kDa BV-specific nucleocapsid protein was identified as AC66, which is known to be required for BV production and was shown by coimmunoprecipitation and mass spectrometry to interact with AC141. Confocal microscopy also showed that AC141, AC66, and vUbi interact at the nuclear periphery. These results suggest that ubiquitination of nucleocapsid proteins by vUbi functions as a signal to determine if a nucleocapsid will egress from the nucleus and form BV or remain in the nucleus to form ODV.IMPORTANCE Baculoviruses produce two types of virions called occlusion-derived virus (ODV) and budded virus (BV). ODVs are required for oral infection, whereas BV enables the systemic spread of virus to all host tissues, which is critical for killing insects. One of the important steps for BV production is the export of nucleocapsids out of the nucleus. This study investigated the molecular mechanisms that enable the selection of nucleocapsids for nuclear export instead of being retained within the nucleus, where they would become ODV. Our data show that ubiquitination, a universal cellular process, specifically tags nucleocapsids of BV, but not those found in ODV, using a virus-encoded ubiquitin (vUbi). Therefore, ubiquitination may be the molecular signal that determines if a nucleocapsid is destined to form a BV, thus ensuring lethal infection of the host.

How Toll Met Hippo.

Toll and Hippo are two seemingly disparate pathways that regulate innate immunity and tissue growth, respectively. Reporting recently in Cell, Liu et al. (2016) tie them together by demonstrating that microbial infection activates Toll, which then signals to both pathways to modulate the antimicrobial response.

Bunched and Madm Function Downstream of Tuberous Sclerosis Complex to Regulate the Growth of Intestinal Stem Cells in Drosophila.

The Drosophila adult midgut contains intestinal stem cells that support homeostasis and repair. We show here that the leucine zipper protein Bunched and the adaptor protein Madm are novel regulators of intestinal stem cells. MARCM mutant clonal analysis and cell type specific RNAi revealed that Bunched and Madm were required within intestinal stem cells for proliferation. Transgenic expression of a tagged Bunched showed a cytoplasmic localization in midgut precursors, and the addition of a nuclear localization signal to Bunched reduced its function to cooperate with Madm to increase intestinal stem cell proliferation. Furthermore, the elevated cell growth and 4EBP phosphorylation phenotypes induced by loss of Tuberous Sclerosis Complex or overexpression of Rheb were suppressed by the loss of Bunched or Madm. Therefore, while the mammalian homolog of Bunched, TSC-22, is able to regulate transcription and suppress cancer cell proliferation, our data suggest the model that Bunched and Madm functionally interact with the TOR pathway in the cytoplasm to regulate the growth and subsequent division of intestinal stem cells.

The conserved misshapen-warts-Yorkie pathway acts in enteroblasts to regulate intestinal stem cells in Drosophila.

Similar to the mammalian intestine, the Drosophila adult midgut has resident stem cells that support growth and regeneration. How the niche regulates intestinal stem cell activity in both mammals and flies is not well understood. Here, we show that the conserved germinal center protein kinase Misshapen restricts intestinal stem cell division by repressing the expression of the JAK-STAT pathway ligand Upd3 in differentiating enteroblasts. Misshapen, a distant relative to the prototypic Warts activating kinase Hippo, interacts with and activates Warts to negatively regulate the activity of Yorkie and the expression of Upd3. The mammalian Misshapen homolog MAP4K4 similarly interacts with LATS (Warts homolog) and promotes inhibition of YAP (Yorkie homolog). Together, this work reveals that the Misshapen-Warts-Yorkie pathway acts in enteroblasts to control niche signaling to intestinal stem cells. These findings also provide a model in which to study requirements for MAP4K4-related kinases in MST1/2-independent regulation of LATS and YAP.

Enteroendocrine cells support intestinal stem-cell-mediated homeostasis in Drosophila.

Intestinal stem cells in the adult Drosophila midgut are regulated by growth factors produced from the surrounding niche cells including enterocytes and visceral muscle. The role of the other major cell type, the secretory enteroendocrine cells, in regulating intestinal stem cells remains unclear. We show here that newly eclosed scute loss-of-function mutant flies are completely devoid of enteroendocrine cells. These enteroendocrine cell-less flies have normal ingestion and fecundity but shorter lifespan. Moreover, in these newly eclosed mutant flies, the diet-stimulated midgut growth that depends on the insulin-like peptide 3 expression in the surrounding muscle is defective. The depletion of Tachykinin-producing enteroendocrine cells or knockdown of Tachykinin leads to a similar although less severe phenotype. These results establish that enteroendocrine cells serve as an important link between diet and visceral muscle expression of an insulin-like growth factor to stimulate intestinal stem cell proliferation and tissue growth.

Defining the roles of the baculovirus regulatory proteins IE0 and IE1 in genome replication and early gene transactivation.

IE0 and IE1 of the baculovirus Autographa californica multiple nucleopolyhedrovirus are essential transregulatory proteins required for both viral DNA replication and transcriptional transactivation. IE0 is identical to IE1 except for 54 amino acids at the N-terminus but the functional differences between these two proteins remain unclear. The purpose of this study was to determine the separate roles of these critical proteins in the virus life cycle. Unlike prior studies, IE0 and IE1 were analyzed using viruses that expressed ie0 and ie1 from an identical promoter so that the timing and levels of expression were comparable. IE0 and IE1 were found to equally support viral DNA replication and budded virus (BV) production. However, specific viral promoters were selectively transactivated by IE0 relative to IE1 but only when expressed at low levels. These results indicate that IE0 preferentially transactivates specific viral genes at very early times post-infection enabling accelerated replication and BV production.

TLR sorting by Rab11 endosomes maintains intestinal epithelial-microbial homeostasis.

Compartmentalization of Toll-like receptors (TLRs) in intestinal epithelial cells (IECs) regulates distinct immune responses to microbes; however, the specific cellular machinery that controls this mechanism has not been fully identified. Here we provide genetic evidences that the recycling endosomal compartment in enterocytes maintains a homeostatic TLR9 intracellular distribution, supporting mucosal tolerance to normal microbiota. Genetic ablation of a recycling endosome resident small GTPase, Rab11a, a gene adjacent to a Crohn's disease risk locus, in mouse IECs and in Drosophila midgut caused epithelial cell-intrinsic cytokine production, inflammatory bowel phenotype, and early mortality. Unlike wild-type controls, germ-free Rab11a-deficient mouse intestines failed to tolerate the intraluminal stimulation of microbial agonists. Thus, Rab11a endosome controls intestinal host-microbial homeostasis at least partially via sorting TLRs.

Gene expression profiling identifies the zinc-finger protein Charlatan as a regulator of intestinal stem cells in Drosophila.

Intestinal stem cells (ISCs) in the adult Drosophila midgut can respond to tissue damage and support repair. We used genetic manipulation to increase the number of ISC-like cells in the adult midgut and performed gene expression profiling to identify potential ISC regulators. A detailed analysis of one of these potential regulators, the zinc-finger protein Charlatan, was carried out. MARCM clonal analysis and RNAi in precursor cells showed that loss of Chn function caused severe ISC division defects, including loss of EdU incorporation, phosphorylated histone 3 staining and expression of the mitotic protein Cdc2. Loss of Charlatan also led to a much reduced histone acetylation staining in precursor cells. Both the histone acetylation and ISC division defects could be rescued by the simultaneous decrease of the Histone Deacetylase 2. The overexpression of Charlatan blocked differentiation reversibly, but loss of Charlatan did not lead to automatic differentiation. The results together suggest that Charlatan does not simply act as an anti-differentiation factor but instead functions to maintain a chromatin structure that is compatible with stem cell properties, including proliferation.

Regulation of Toll signaling and inflammation by ß-arrestin and the SUMO protease Ulp1.

The Toll signaling pathway has a highly conserved function in innate immunity and is regulated by multiple factors that fine tune its activity. One such factor is ß-arrestin Kurtz (Krz), which we previously implicated in the inhibition of developmental Toll signaling in the Drosophila melanogaster embryo. Another level of controlling Toll activity and immune system homeostasis is by protein sumoylation. In this study, we have uncovered a link between these two modes of regulation and show that Krz affects sumoylation via a conserved protein interaction with a SUMO protease, Ulp1. Loss of function of krz or Ulp1 in Drosophila larvae results in a similar inflammatory phenotype, which is manifested as increased lamellocyte production; melanotic mass formation; nuclear accumulation of Toll pathway transcriptional effectors, Dorsal and Dif; and expression of immunity genes, such as Drosomycin. Moreover, mutations in krz and Ulp1 show dosage-sensitive synergistic genetic interactions, suggesting that these two proteins are involved in the same pathway. Using Dorsal sumoylation as a readout, we found that altering Krz levels can affect the efficiency of SUMO deconjugation mediated by Ulp1. Our results demonstrate that ß-arrestin controls Toll signaling and systemic inflammation at the level of sumoylation.

Analysis of the autographa californica multiple nucleopolyhedrovirus overlapping gene pair lef3 and ac68 reveals that AC68 is a per os infectivity factor and that LEF3 is critical, but not essential, for virus replication.

Autographa californica multiple nucleopolyhedrovirus ac68 is a core gene that overlaps lef3 which encodes the single-stranded DNA binding protein. A knockout (KO) virus lacking both lef3 and ac68 was generated (lef3-ac68 2×KO) to enable the functional study of ac68. To produce an ac68KO virus that did not impact lef3 expression, the lef3-ac68 2×KO virus was repaired with a DNA fragment containing lef3 and ac68, in which ac68 contained point mutations so that only LEF3 was expressed. Repair of lef3-ac68 2×KO with just ac68 generated an lef3KO virus. Analysis of the ac68KO virus showed that viral DNA replication and budded virus (BV) levels were unaffected compared to levels in the double-repair or wild-type (WT) control virus. Bioassay analyses of Trichoplusia ni larvae injected with BV directly into the hemolymph, bypassing the gut, showed no difference in mortality rates between the ac68KO and the WT viruses. However, in oral bioassays the ac68KO occlusion bodies failed to kill larvae. These results show that the core gene ac68 encodes a per os infectivity factor (pif6). The lef3KO virus was also analyzed, and virus replication was drastically reduced compared to WT virus, but very low levels of lef3KO virus DNA replication and BV production could be detected. In addition, in transfected cells P143 was transported to the nucleus in the absence of LEF3. This study therefore shows for the first time that even though the loss of LEF3 severely impairs virus replication, it is not absolutely essential for P143 nuclear import or viral replication.

Autographa californica multiple nucleopolyhedrovirus core gene ac92 (p33) is required for efficient budded virus production.

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac92 is a core gene encoding a protein associated with occlusion derived virus (ODV), binds human P53 and also has flavin adenine dinucleotide linked sulfhydryl oxidase activity but its role in the virus life cycle is not known. To determine ac92 function a deletion virus (vAc(92KO)) was generated and transfected Sf9 cells revealed that vAc(92KO) infection was restricted primarily to single cells and budded virus (BV) titer was reduced over 99.99%. However, viral DNA replication was unaffected and development of occlusion bodies in vAc(92KO)-transfected cells evidenced progression to very late phases of viral infection. AC92 localized to both the cytoplasm and nucleus, and was also associated with BV as well as ODV. In BV AC92 was detected in BV envelope and nucleocapsid fractions. Finally it was shown that the ac92 homologue from the Group II alphabaculovirus Mamestra configurata NPV maco96 could only partially rescue vAc(92KO).

Deletion of AcMNPV AC16 and AC17 results in delayed viral gene expression in budded virus infected cells but not transfected cells.

This study investigated the combined function of the Autographa californica multiple nucleopolyhedrovirus overlapping genes ac16 (BV/ODV-E26, DA26) and ac17. Ac17 is a late gene and the promoter is within the ac16 open reading frame. A double ac16-ac17 knockout virus was generated to assess the function of each gene independently or together. Loss of ac17 did not affect viral DNA synthesis but budded virus (BV) production was reduced. Deletion of both ac16-ac17 resulted in reduced viral DNA synthesis and a further reduction in BV production. In BV infected Sf9 cells, viral gene expression was delayed up to 12 h in the absence of both AC16 and AC17 but not if either gene was present. Cells infected by transfecting viral DNA, by-passing the BV particle, exhibited no delay in gene expression from the double knockout virus. AC16 and AC17 are therefore required for rapid viral gene expression in cells infected by BV.

Autographa californica multiple nucleopolyhedrovirus core gene ac96 encodes a per Os infectivity factor (PIF-4).

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac96 is a core gene, but its role in virus replication is still unknown. To determine its role in the baculovirus life cycle, we used the AcMNPV bacmid system to generate an ac96-null virus (vAc(96)(null)). Our analyses showed that the absence of ac96 does not affect budded virus (BV) production or viral DNA replication in infected Sf9 cells. Western blotting and confocal immunofluorescence analysis showed that AC96 is expressed in both the cytoplasm and the nucleus throughout infection. In addition, AC96 was detected in the envelope fractions of both BV and occlusion-derived virus. Injection of vAc(96)(null) BV into the hemocoel killed Trichoplusia ni larvae as efficiently as repaired and control viruses; however, vAc(96)(null) was unable to infect the midgut tissue of Trichoplusia ni larvae when inoculated per os. Therefore, the results of this study show that ac96 encodes a new per os infectivity factor (PIF-4).

Deletion of the AcMNPV core gene ac109 results in budded virions that are non-infectious.

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac109 is a core gene and its function in the virus life cycle is unknown. To determine its role in the baculovirus life cycle, we used the AcMNPV bacmid system to generate an ac109 deletion virus (vAc(109KO)). Fluorescence and light microscopy showed that transfection of vAc(109KO) results in a single-cell infection phenotype. Viral DNA replication is unaffected and the development of occlusion bodies in vAc(109KO)-transfected cells evidenced progression to the very late phases of viral infection. Western blot and confocal immunofluorescence analysis showed that AC109 is expressed in the cytoplasm and nucleus throughout infection. In addition, AC109 is a structural protein as it was detected in both budded virus (BV) and occlusion derived virus in both the envelope and nucleocapsid fractions. Titration assays by qPCR and TCID(50) showed that vAc(109KO) produced BV but the virions are non-infectious. The vAc(109KO) BV were indistinguishable from the BV of repaired and wild type control viruses as determined by negative staining and electron microscopy.

AcMNPV AC16 (DA26, BV/ODV-E26) regulates the levels of IE0 and IE1 and binds to both proteins via a domain located within the acidic transcriptional activation domain.

IE0 and IE1 are the primary viral regulatory proteins of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) involved in the transactivation of early genes, stimulation of late gene expression, and viral DNA replication. The protein interactions required for IE0 or IE1 to achieve these varied roles are not well defined, so to identify proteins that interact with IE0 and IE1, tandem affinity purification (TAP) and LC-MS/MS was used. Analysis of purified proteins identified AC16 (DA26, BV/ODV-E26) from TAP tagged IE0 virus infected Sf9 cells. Co-immunoprecipitation confirmed that AC16 interacts with both IE0 and IE1 and yeast 2-hybrid analysis mapped the domain required for interaction with AC16. Mutation of the AC16 binding domain enhanced BV production by viruses expressing only IE0 but had no effect if only IE1 is expressed. An ac16 deletion virus was constructed and was shown not to affect the temporal expression of IE0 and IE1; however the relative level of IE0 to IE1 was significantly increased.