Epithelial cell-turnover ensures robust coordination of tissue growth in Drosophila ribosomal protein mutants

体の成長と組織の成長の速度を調節する仕組みをハエで解明 --進化のメカニズムに関わる可能性--. 京都大学プレスリリース. 2021-01-29.Highly reproducible tissue development is achieved by robust, time-dependent coordination of cell proliferation and cell death. To study the mechanisms underlying robust tissue growth, we analyzed the developmental process of wing imaginal discs in Drosophila Minute mutants, a series of heterozygous mutants for a ribosomal protein gene. Minute animals show significant developmental delay during the larval period but develop into essentially normal flies, suggesting there exists a mechanism ensuring robust tissue growth during abnormally prolonged developmental time. Surprisingly, we found that both cell death and compensatory cell proliferation were dramatically increased in developing wing pouches of Minute animals. Blocking the cell-turnover by inhibiting cell death resulted in morphological defects, indicating the essential role of cell-turnover in Minute wing morphogenesis. Our analyses showed that Minute wing discs elevate Wg expression and JNK-mediated Dilp8 expression that causes developmental delay, both of which are necessary for the induction of cell-turnover. Furthermore, forced increase in Wg expression together with developmental delay caused by ecdysone depletion induced cell-turnover in the wing pouches of non-Minute animals. Our findings suggest a novel paradigm for robust coordination of tissue growth by cell-turnover, which is induced when developmental time axis is distorted

Elimination of oncogenic cells that regulate epithelial homeostasis in Drosophila

Normal epithelial tissues often put anti‐tumorigenic pressure on newly emerged oncogenic cells through cell–cell communications. In Drosophila epithelium, clones of oncogenic cells mutant for evolutionarily conserved apico‐basal polarity genes such as scribble (scrib) and discs large (dlg) are actively eliminated when surrounded by normal cells. It has been reported that c‐Jun N‐terminal kinase (JNK) signaling in polarity‐deficient cells is crucial for their cell death. However, the mechanism by which normal epithelial tissues exert anti‐tumorigenic effects on polarity‐deficient cells had been elusive. Here, I describe our genetic studies in Drosophila epithelium especially focused on the role of surrounding normal epithelial cells in response to the emergence of polarity‐deficient cells. Furthermore, I also describe recent studies regarding the mechanism by which polarity‐deficient cells are extruded from the tissue, and discuss future perspectives on the study of cell–cell communications in epithelial homeostasis

JNK and Yorkie drive tumor progression by generating polyploid giant cells in Drosophila

Epithelial cancer tissues often possess polyploid giant cells, which are thought to be highly oncogenic. However, the mechanisms by which polyploid giant cells are generated in tumor tissues and how such cells contribute to tumor progression remain elusive. We previously noticed in Drosophila imaginal epithelium that cells mutant for the endocytic gene rab5 exhibit enlarged nuclei. Here we find that mutations in endocytic ‘neoplastic tumor-suppressor’ genes, such as rab5, vps25, erupted, or avalanche result in generation of polyploid giant cells. Genetic analyses on rab5-defective cells reveal that cooperative activation of JNK and Yorkie generates polyploid giant cells via endoreplication. Mechanistically, Yorkie-mediated upregulation of Diap1 cooperates with JNK to downregulate the G2/M cyclin CycB, thereby inducing endoreplication. Interestingly, malignant tumors induced by Ras activation and cell polarity defect also consist of polyploid giant cells, which are generated by JNK and Yorkie-mediated downregulation of CycB. Strikingly, elimination of polyploid giant cells from such malignant tumors by blocking endoreplication strongly suppressed tumor growth and metastatic behavior. Our observations suggest that JNK and Yorkie, two oncogenic proteins activated in many types of human cancers, cooperatively drive tumor progression by generating oncogenic polyploid giant cells

JNK and Yorkie drive tumor malignancy by inducing L-amino acid transporter 1 in Drosophila

Identifying a common oncogenesis pathway among tumors with different oncogenic mutations is critical for developing anti-cancer strategies. Here, we performed transcriptome analyses on two different models of Drosophila malignant tumors caused by Ras activation with cell polarity defects (RasV12/scrib-/-) or by microRNA bantam overexpression with endocytic defects (bantam/rab5-/-), followed by an RNAi screen for genes commonly essential for tumor growth and malignancy. We identified that Juvenile hormone Inducible-21 (JhI-21), a Drosophila homolog of the L-amino acid transporter 1 (LAT1), is upregulated in these malignant tumors with different oncogenic mutations and knocking down of JhI-21 strongly blocked their growth and invasion. JhI-21 expression was induced by simultaneous activation of c-Jun N-terminal kinase (JNK) and Yorkie (Yki) in these tumors and thereby contributed to tumor growth and progression by activating the mTOR-S6 pathway. Pharmacological inhibition of LAT1 activity in Drosophila larvae significantly suppressed growth of RasV12/scrib-/- tumors. Intriguingly, LAT1 inhibitory drugs did not suppress growth of bantam/rab5-/- tumors and overexpression of bantam rendered RasV12/scrib-/- tumors unresponsive to LAT1 inhibitors. Further analyses with RNA sequencing of bantam-expressing clones followed by an RNAi screen suggested that bantam induces drug resistance against LAT1 inhibitors via downregulation of the TMEM135-like gene CG31157. Our observations unveil an evolutionarily conserved role of LAT1 induction in driving Drosophila tumor malignancy and provide a powerful genetic model for studying cancer progression and drug resistance

Coronin-1 promotes directional cell rearrangement in Drosophila wing epithelium

Directional cell rearrangement is a critical process underlying correct tissue deformation during morphogenesis. Although the involvement of F-actin regulation in cell rearrangement has been established, the role and regulation of actin binding proteins (ABPs) in this process are not well understood. In this study, we investigated the function of Coronin-1, a WD-repeat actin-binding protein, in controlling directional cell rearrangement in the Drosophila pupal wing. Transgenic flies expressing Coronin-1-EGFP were generated using CRISPR-Cas9. We observed that Coronin-1 localizes at the reconnecting junction during cell rearrangement, which is dependent on actin interacting protein 1 (AIP1) and cofilin, actin disassemblers and known regulators of wing cell rearrangement. Loss of Coronin-1 function reduces cell rearrangement directionality and hexagonal cell fraction. These results suggest that Coronin-1 promotes directional cell rearrangement via its interaction with AIP1 and cofilin, highlighting the role of ABPs in the complex process of morphogenesis. Key words: morphogenesis, cell rearrangement, actin binding proteins (ABPs

JNK-mediated Slit-Robo signaling facilitates epithelial wound repair by extruding dying cells

Multicellular organisms repair injured epithelium by evolutionarily conserved biological processes including activation of c-Jun N-terminal kinase (JNK) signaling. Here, we show in Drosophila imaginal epithelium that physical injury leads to the emergence of dying cells, which are extruded from the wounded tissue by JNK-induced Slit-Roundabout2 (Robo2) repulsive signaling. Reducing Slit-Robo2 signaling in the wounded tissue suppresses extrusion of dying cells and generates aberrant cells with highly upregulated growth factors Wingless (Wg) and Decapentaplegic (Dpp). The inappropriately elevated Wg and Dpp impairs wound repair, as halving one of these growth factor genes cancelled wound healing defects caused by Slit-Robo2 downregulation. Our data suggest that JNK-mediated Slit-Robo2 signaling contributes to epithelial wound repair by promoting extrusion of dying cells from the wounded tissue, which facilitates transient and appropriate induction of growth factors for proper wound healing

JNK and Yorkie drive tumor malignancy by inducing L-amino acid transporter 1 in Drosophila

Identifying a common oncogenesis pathway among tumors with different oncogenic mutations is critical for developing anti-cancer strategies. Here, we performed transcriptome analyses on two different models of Drosophila malignant tumors caused by Ras activation with cell polarity defects (RasV12/scrib-/-) or by microRNA bantam overexpression with endocytic defects (bantam/rab5-/-), followed by an RNAi screen for genes commonly essential for tumor growth and malignancy. We identified that Juvenile hormone Inducible-21 (JhI-21), a Drosophila homolog of the L-amino acid transporter 1 (LAT1), is upregulated in these malignant tumors with different oncogenic mutations and knocking down of JhI-21 strongly blocked their growth and invasion. JhI-21 expression was induced by simultaneous activation of c-Jun N-terminal kinase (JNK) and Yorkie (Yki) in these tumors and thereby contributed to tumor growth and progression by activating the mTOR-S6 pathway. Pharmacological inhibition of LAT1 activity in Drosophila larvae significantly suppressed growth of RasV12/scrib-/- tumors. Intriguingly, LAT1 inhibitory drugs did not suppress growth of bantam/rab5-/- tumors and overexpression of bantam rendered RasV12/scrib-/- tumors unresponsive to LAT1 inhibitors. Further analyses with RNA sequencing of bantam-expressing clones followed by an RNAi screen suggested that bantam induces drug resistance against LAT1 inhibitors via downregulation of the TMEM135-like gene CG31157. Our observations unveil an evolutionarily conserved role of LAT1 induction in driving Drosophila tumor malignancy and provide a powerful genetic model for studying cancer progression and drug resistance

Competition for Space Is Controlled by Apoptosis-Induced Change of Local Epithelial Topology

During the initial stage of tumor progression, oncogenic cells spread despite spatial confinement imposed by surrounding normal tissue. This spread of oncogenic cells (winners) is thought to be governed by selective killing of surrounding normal cells (losers) through a phenomenon called “cell competition” (i.e., supercompetition). Although the mechanisms underlying loser elimination are increasingly apparent, it is not clear how winner cells selectively occupy the space made available following loser apoptosis. Here, we combined live imaging analyses of two different oncogenic clones (Yki/YAP activation and Ras activation) in the Drosophila epithelium with computer simulation of tissue mechanics to elucidate such a mechanism. Contrary to the previous expectation that cell volume loss after apoptosis of loser cells was simply compensated for by the faster proliferation of winner cells, we found that the lost volume was compensated for by rapid cell expansion of winners. Mechanistically, the rapid winner-dominated cell expansion was driven by apoptosis-induced epithelial junction remodeling, which causes re-connection of local cellular connectivity (cell topology) in a manner that selectively increases winner apical surface area. In silico experiments further confirmed that repetition of loser elimination accelerates tissue-scale winner expansion through topological changes over time. Our proposed mechanism for linking loser death and winner expansion provides a new perspective on how tissue homeostasis disruption can initiate from an oncogenic mutation