An EMC-Hpo-Yki axis maintains intestinal homeostasis under physiological and pathological conditions.

Balanced control of stem cell proliferation and differentiation underlines tissue homeostasis. Disruption of tissue homeostasis often results in many diseases. However, how endogenous factors influence the proliferation and differentiation of intestinal stem cells (ISCs) under physiological and pathological conditions remains poorly understood. Here, we find that the evolutionarily conserved endoplasmic reticulum membrane protein complex (EMC) negatively regulates ISC proliferation and intestinal homeostasis. Compromising EMC function in progenitors leads to excessive ISC proliferation and intestinal homeostasis disruption. Mechanistically, the EMC associates with and stabilizes Hippo (Hpo) protein, the key component of the Hpo signaling pathway. In the absence of EMC, Yorkie (Yki) is activated to promote ISC proliferation due to Hpo destruction. The EMC-Hpo-Yki axis also functions in enterocytes to maintain intestinal homeostasis. Importantly, the levels of the EMC are dramatically diminished in tunicamycin-treated animals, leading to Hpo destruction, thereby resulting in intestinal homeostasis disruption due to Yki activation. Thus, our study uncovers the molecular mechanism underlying the action of the EMC in intestinal homeostasis maintenance under physiological and pathological conditions and provides new insight into the pathogenesis of tunicamycin-induced tumorigenesis.

Silence of yki by miR-7 regulates the Hippo pathway.

The Hippo signaling pathway governs organ size via coordinating cell proliferation and apoptosis, and its dysregulation causes congenital diseases and cancers. The homeostasis of Hippo pathway is achieved through multiple post translational modifications. Through Drosophila genetic screening, we found that miRNAs were also involved in Hippo pathway regulation. Here, we showed that overexpression of miR-7 resulted in small wings, which were neutralized by miR-7-sponge (miR-7-sp) co-expression. Mechanistically, miR-7 inhibited the expression of Hippo pathway target genes. Epistatic analyses revealed that miR-7 modulated Hippo pathway through the transcriptional cofactor Yorkie (Yki). Consistently, overexpression of miR-7 decreased Yki protein. We further found a seed sequence of miR-7 in the yki 3'-UTR region. In addition, we discovered that miR-7 was a transcriptional target of Yki. Thus, a negative feedback loop existed for fine tuning Hippo pathway activity. Taken together, our findings uncovered a novel mechanism by which Yki was silenced by miR-7 for Hippo pathway regulation.

HERC4 exerts an anti-tumor role through destabilizing the oncoprotein Smo.

The GPCR-like transmembrane protein Smoothened (Smo) is an indispensable transducer in Hedgehog (Hh) pathway, its hyperactivation leads to several human cancers, including non-small cell lung cancer (NSCLC). The mechanism governing Smo stability still remains elusive. Here, we perform a modifier screening in Drosophila, and find that the E3 ligase dHerc4 degrades dSmo. Depletion of dherc4 increases dSmo protein and activates Hh pathway. In addition, we reveal that HERC4 is downregulated in NSCLC samples, negative correlating with Smo. HERC4 interacts with Smo reciprocally in NSCLC cells. Finally, we show that knockdown of herc4 activates Hh pathway and promotes NSCLC cell proliferation. Taken together, our studies have demonstrated that HERC4 acts as a tumor suppressor via destabilizing the oncoprotein Smo, and provided HERC4 as a promising therapeutic target for NSCLC treatment.

The transcriptional factor Apt regulates neuroblast differentiation through activating CycE expression.

In Drosophila, the thoracic neuroblast 6-4 (NB6-4T) divides asymmetrically into a glial precursor and a neuronal precursor, while the abdominal neuroblast 6-4 (NB6-4A) divides symmetrically to produce two glial cells. The underlying mechanism by which NB6-4T and NB6-4A undergo distinct differentiation is still elusive. Here, we find that the transcription factor Apontic (Apt) exclusively expresses in NB6-4T cells and is involved in regulating NB6-4T differentiation. Loss of Apt results in neuronal precursor loss. Epistasis analysis shows that Apt controls NB6-4T differentiation through activating CycE expression. On the other hand, Gcm suppresses Apt expression in the NB6-4A cell, thus inhibiting CycE expression. Taken together, our findings reveal a Gcm-Apt-CycE axis that regulates neuroblast and glia cell differentiation.

Usp7 promotes medulloblastoma cell survival and metastasis by activating Shh pathway.

The ubiquitin-specific protease Usp7 plays roles in multiple cellular processes through deubiquitinating and stabilizing numerous substrates, including P53, Pten and Gli. Aberrant Usp7 activity has been implicated in many disorders and tumorigenesis, making it as a potential target for therapeutic intervention. Although it is clear that Usp7 is involved in many types of cancer, its role in regulating medulloblastoma (MB) is still unknown. In this study, we show that knockdown of Usp7 inhibits the proliferation and migration of MB cells, while Usp7 overexpression exerts an opposite effect. Furthermore, we establish Usp7 knockout MB cell line using the CRISPR/Cas9 system and further confirm that Usp7 knockout also blocks MB cell proliferation and metastasis. In addition, we reveal that knockdown of Usp7 compromises Shh pathway activity and decrease Gli protein levels, while P53 level and P53 target gene expression have no obvious changes. Finally, we find that Usp7 inhibitors apparently inhibit MB cell viability and migration. Taken together, our findings suggest that Usp7 is important for MB cell proliferation and metastasis by activating Shh pathway, and is a putative therapeutic target for MBs.

Phosphorylation of LZTS2 by PLK1 activates the Wnt pathway.

Lung adenocarcinoma (LUAD), responsible for nearly half of lung cancer cases, is one of the most prevalent and lethal malignant tumors globally. There is increasing evidence suggesting that the oncoprotein PLK1 plays a role in the onset and advancement of different types of cancer, including LUAD. Nonetheless, the precise mechanism by which PLK1 promotes tumorigenesis remains unclear. In this study, we demonstrate the upregulation of PLK1 in LUAD samples, which leads to a poor prognosis for LUAD patients. Intriguingly, PLK1 enables to bind to LZTS2 and promote its phosphorylation without affecting LZTS2 degradation. Furthermore, we identify that Ser451 is a key phosphorylation site in LZTS2 protein. LZTS2 exerts an anti-tumor effect by restricting the translocation of the transcription factor ß-Catenin into the nucleus, thereby suppressing the Wnt pathway. PLK1 disrupts the interaction between LZTS2 and ß-Catenin, resulting in the nuclear accumulation of ß-Catenin and the activation of the Wnt pathway. Additionally, we reveal that LZTS2 inhibits the proliferation and migration of LUAD cells, which is rescued by PLK1. Finally, PLK1 inhibitors exhibit a dose-dependent suppression of LUAD cell proliferation and migration. Collectively, this study uncovers the pro-tumorigenic mechanism of PLK1, positioning it as a promising therapeutic target for Wnt-related LUAD.

miR-927 regulates insect wing development by targeting the Hippo pathway.

How organ size is determined is a fundamental question in life sciences. Recent studies have highlighted the importance of the Hippo pathway in regulating organ size. This pathway controls cell proliferation and cell death to maintain the proper number of cells. The activity of the Hippo pathway is tightly fine-tuned through various post-translational modifications, such as phosphorylation and ubiquitination. Here, we discover that miR-927 is a novel regulator of wing size. Overexpression of miR-927 decreases wing size, which can be rescued by co-expressing miR-927-sponge. Next, we show that miR-927 stimulates apoptosis and suppresses the expression of Drosophila inhibitor of apoptosis protein 1, a well-known target gene of the Hippo pathway. Genetic epistatic analyses position miR-927 upstream of Yorkie (Yki) to modulate the Hippo pathway. In addition, there is a matching miR-927 seed site in the yki 3' untranslated region (3'-UTR), and we demonstrate that yki 3'-UTR is the direct target of miR-927. Ultimately, our study reveals that the targeting of yki by miR-927 to regulate the Hippo pathway is conserved in Helicoverpa armigera. Administration of miR-927 via star polycation (SPc) nanocarrier effectively inhibits wing development in H. armigera. Taken together, our findings uncover a novel mechanism by which Yki is silenced at the post-transcriptional level by miR-927, and provide a new perspective on pest management.

The AAA-ATPase Ter94 regulates wing size in Drosophila by suppressing the Hippo pathway.

Insect wing development is a fascinating and intricate process that involves the regulation of wing size through cell proliferation and apoptosis. In this study, we find that Ter94, an AAA-ATPase, is essential for proper wing size dependently on its ATPase activity. Loss of Ter94 enables the suppression of Hippo target genes. When Ter94 is depleted, it results in reduced wing size and increased apoptosis, which can be rescued by inhibiting the Hippo pathway. Biochemical experiments reveal that Ter94 reciprocally binds to Mer, a critical upstream component of the Hippo pathway, and disrupts its interaction with Ex and Kib. This disruption prevents the formation of the Ex-Mer-Kib complex, ultimately leading to the inactivation of the Hippo pathway and promoting proper wing development. Finally, we show that hVCP, the human homolog of Ter94, is able to substitute for Ter94 in modulating Drosophila wing size, underscoring their functional conservation. In conclusion, Ter94 plays a positive role in regulating wing size by interfering with the Ex-Mer-Kib complex, which results in the suppression of the Hippo pathway.

SPOP point mutations regulate substrate preference and affect its function.

The adaptor SPOP recruits substrates to CUL3 E3 ligase for ubiquitination and degradation. Structurally, SPOP harbors a MATH domain for substrate recognition, and a BTB domain responsible for binding CUL3. Reported point mutations always occur in SPOP's MATH domain and are through to disrupt affinities of SPOP to substrates, thereby leading to tumorigenesis. In this study, we identify the tumor suppressor IRF2BP2 as a novel substrate of SPOP. SPOP enables to attenuate IRF2BP2-inhibited cell proliferation and metastasis in HCC cells. However, overexpression of wild-type SPOP alone suppresses HCC cell proliferation and metastasis. In addition, a HCC-derived mutant, SPOP-M35L, shows an increased affinity to IRF2BP2 in comparison with wild-type SPOP. SPOP-M35L promotes HCC cell proliferation and metastasis, suggesting that M35L mutation possibly reprograms SPOP from a tumor suppressor to an oncoprotein. Taken together, this study uncovers mutations in SPOP's MATH lead to distinct functional consequences in context-dependent manners, rather than simply disrupting its interactions with substrates, raising a noteworthy concern that we should be prudent to select SPOP as therapeutic target for cancers.

Oxidative stress reprograms the transcriptional coactivator Yki to suppress cell proliferation.

The transcriptional coactivator Yorkie (Yki) regulates organ size by promoting cell proliferation. It is unclear how cells control Yki activity when exposed to harmful stimuli such as oxidative stress. In this study, we show that oxidative stress inhibits the binding of Yki to Scalloped (Sd) but promotes the interaction of Yki with another transcription factor, forkhead box O (Foxo), ultimately leading to a halt in cell proliferation. Mechanistically, Foxo normally exhibits a low binding affinity for Yki, allowing Yki to form a complex with Sd and activate proliferative genes. Under oxidative stress, Usp7 deubiquitinates Foxo to promote its interaction with Yki, thereby activating the expression of proliferation suppressors. Finally, we show that Yki is essential for Drosophila survival under oxidative stress. In summary, these findings suggest that oxidative stress reprograms Yki from a proliferation-promoting factor to a proliferation suppressor, forming a self-protective mechanism.

Transcriptome Analysis Provides Insights into Water Immersion Promoting the Decocooning of Osmia excavata Alfken.

The timing of decocooning and nesting during the flowering period are crucial for the reproduction and pollination activities of Osmia excavata. In order to improve the pollination efficiency of O. excavata, it is crucial to find a way to break the cocoon quickly. Our results showed that the decocooning rates at 6, 12, 24, 36, 48, and 72 h after 30 min of water immersion (WI) were 28.67%, 37.33%, 37.33%, 41.33%, 44.33%, and 53.00%, respectively. The decocooning rate fold of 6 h was 14.33 compared with the control group. Transcriptome sequencing resulted in 273 differentially expressed genes (DEGs) being identified between the WI and control groups. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that muscle-related functions play important roles in O. excavata decocooning in response to WI. Cluster analysis also showed that DEGs in cardiac muscle contraction and adrenergic signaling in cardiomyocytes were up-regulated in response to WI-promoted decocooning. In conclusion, the rate of decocooning can be improved by WI in a short time. During WI-promoted decocooning, muscle-related pathways play an important role. Therefore, the application of this technology will improve the pollination effect of O. excavata.

FSBP suppresses tumor cell migration by inhibiting the JNK pathway.

The main cause of high mortality in cancer patients is tumor metastasis. Exploring the underlying mechanism of tumor metastasis is of great significance for clinical treatments. Here, we identify the transcription factor Apt/FSBP is a suppressor for tumor metastasis. In Drosophila wing disc, knockdown of apt is able to trigger cell migration, whereas overexpression of apt hampers scrib-RNAi-induced tumor cell migration. Further studies show that loss of apt promotes cell migration through activating the JNK pathway. To investigate the role of FSBP, the homolog of Apt in mammals, we construct Fsbp liver-specific knockout mice. Knockout of Fsbp in liver does not cause any detectable physiological defects, but predisposes to tumorigenesis on DEN and CCl4 treatment. In addition, loss of Fsbp accelerates tumor metastasis from liver to diaphragm. Taken together, this study uncovers FSBP is a novel tumor suppressor, and provides it as a considerable drug target for tumor treatment.

Inhibition of the transcription factor ZNF281 by SUFU to suppress tumor cell migration.

Although the Hedgehog (Hh) pathway plays an evolutionarily conserved role from Drosophila to mammals, some divergences also exist. Loss of Sufu, an important component of the Hh pathway, does not lead to an obvious developmental defect in Drosophila. However, in mammals, loss of SUFU results in serious disorder, even various cancers. This divergence suggests that SUFU plays additional roles in mammalian cells, besides regulating the Hh pathway. Here, we identify that the transcription factor ZNF281 is a novel binding partner of SUFU. Intriguingly, the Drosophila genome does not encode any homologs of ZNF281. SUFU is able to suppress ZNF281-induced tumor cell migration and DNA damage repair by inhibiting ZNF281 activity. Mechanistically, SUFU binds ZNF281 to mask the nuclear localization signal of ZNF281, culminating in ZNF281 cytoplasmic retention. In addition, SUFU also hampers the interactions between ZNF281 and promoters of target genes. Finally, we show that SUFU is able to inhibit ZNF281-induced tumor cell migration using an in vivo model. Taken together, these results uncover a Hh-independent mechanism of SUFU exerting the anti-tumor role, in which SUFU suppresses tumor cell migration through antagonizing ZNF281. Therefore, this study provides a possible explanation for the functional divergence of SUFU in mammals and Drosophila.

Usp8 promotes tumor cell migration through activating the JNK pathway.

Tumor metastasis is the most cause of high mortality for cancer patients. Identification of novel factors that modulate tumor cell migration is of great significance for therapeutic strategies. Here, we find that the ubiquitin-specific protease 8 (Usp8) promotes tumor cell migration through activating the c-Jun N-terminal kinase (JNK) pathway. Genetic epistasis analyses uncover Usp8 acts upstream of Tak1 to control the JNK pathway. Consistently, biochemical results reveal that Usp8 binds Tak1 to remove ubiquitin modification from Tak1, leading to its stabilization. In addition, human USP8 also triggers tumor cell migration and activates the JNK pathway. Finally, we show that knockdown of USP8 in human breast cancer cells suppresses cell migration. Taken together, our findings demonstrate that a conserved Usp8-Tak1-JNK axis promotes tumor cell migration, and providing USP8 as a potential therapeutic target for cancer treatment.

The Hh pathway promotes cell apoptosis through Ci-Rdx-Diap1 axis.

Apoptosis is a strictly coordinated process to eliminate superfluous or damaged cells, and its deregulation leads to birth defects and various human diseases. The regulatory mechanism underlying apoptosis still remains incompletely understood. To identify novel components in apoptosis, we carry out a modifier screen and find that the Hh pathway aggravates Hid-induced apoptosis. In addition, we reveal that the Hh pathway triggers apoptosis through its transcriptional target gene rdx, which encodes an E3 ubiquitin ligase. Rdx physically binds Diap1 to promote its K63-linked polyubiquitination, culminating in attenuating Diap1-Dronc interaction without affecting Diap1 stability. Taken together, our findings unexpectedly uncover the oncogenic Hh pathway is able to promote apoptosis through Ci-Rdx-Diap1 module, raising a concern to choose Hh pathway inhibitors as anti-tumor drugs.

Hippo signaling suppresses tumor cell metastasis via a Yki-Src42A positive feedback loop.

Metastasis is an important cause of death from malignant tumors. It is of great significance to explore the molecular mechanism of metastasis for the development of anti-cancer drugs. Here, we find that the Hippo pathway hampers tumor cell metastasis in vivo. Silence of hpo or its downstream wts promotes tumor cell migration in a Yki-dependent manner. Furthermore, we identify that inhibition of the Hippo pathway promotes tumor cell migration through transcriptional activating src42A, a Drosophila homolog of the SRC oncogene. Yki activates src42A transcription through direct binding its intron region. Intriguingly, Src42A further increases Yki transcriptional activity to form a positive feedback loop. Finally, we show that SRC is also a target of YAP and important for YAP to promote the migration of human hepatocellular carcinoma cells. Together, our findings uncover a conserved Yki/YAP-Src42A/SRC positive feedback loop promoting tumor cell migration and provide SRC as a potential therapeutic target for YAP-driven metastatic tumors.

Dual functions of Rack1 in regulating Hedgehog pathway.

Hedgehog (Hh) pathway plays multiple roles in many physiological processes and its dysregulation leads to congenital disorders and cancers. Hh regulates the cellular localization of Smoothened (Smo) and the stability of Cubitus interruptus (Ci) to fine-tune the signal outputs. However, the underlying mechanisms are still unclear. Here, we show that the scaffold protein Rack1 plays dual roles in Hh signaling. In the absence of Hh, Rack1 promotes Ci and Cos2 to form a Ci-Rack1-Cos2 complex, culminating in Slimb-mediated Ci proteolysis. In the presence of Hh, Rack1 dissociates from Ci-Rack1-Cos2 complex and forms a trimeric complex with Smo and Usp8, leading to Smo deubiquitination and cell surface accumulation. Furthermore, we find the regulation of Rack1 on Hh pathway is conserved from Drosophila to mammalian cells. Our findings demonstrate that Rack1 plays dual roles during Hh signal transduction and provide Rack1 as a potential drug target for Hh-related diseases.

Evolutionarily Conserved Roles for Apontic in Induction and Subsequent Decline of Cyclin E Expression.

Cyclin E is a key factor for S phase entry, and deregulation of Cyclin E results in developmental defects and tumors. Therefore, proper cycling of Cyclin E is crucial for normal growth. Here we found that transcription factors Apontic (Apt) and E2f1 cooperate to induce cyclin E in Drosophila. Functional binding motifs of Apt and E2f1 are clustered in the first intron of Drosophila cyclin E and directly contribute to the cyclin E transcription. Knockout of apt and e2f1 together abolished Cyclin E expression. Furthermore, Apt up-regulates Retinoblastoma family protein 1 (Rbf1) for proper chromatin compaction, which is known to repress cyclin E. Notably, Apt-dependent up-regulation of Cyclin E and Rbf1 is evolutionarily conserved in mammalian cells. Our findings reveal a unique mechanism underlying the induction and subsequent decline of Cyclin E expression.

Usp7 regulates Hippo pathway through deubiquitinating the transcriptional coactivator Yorkie.

The Hippo pathway plays an important role in organ development and adult tissue homeostasis, and its deregulation has been implicated in many cancers. The Hippo signaling relies on a core kinase cascade culminating in phosphorylation of the transcription coactivator Yorkie (Yki). Although Yki is the key effector of Hippo pathway, the regulation of its protein stability is still unclear. Here, we show that Hippo pathway attenuates the binding of a ubiquitin-specific protease Usp7 to Yki, which regulates Hippo signaling through deubiquitinating Yki. Furthermore, the mammalian homolog of Usp7, HAUSP plays a conserved role in regulating Hippo pathway by modulating Yap ubiquitination and degradation. Finally, we find that the expression of HAUSP is positively correlated with that of Yap, both showing upregulated levels in clinical hepatocellular carcinoma (HCC) specimens. In summary, our findings demonstrate that Yki/Yap is stabilized by Usp7/HAUSP, and provide HAUSP as a potential therapeutic target for HCC.

The deubiquitinase UCHL5/UCH37 positively regulates Hedgehog signaling by deubiquitinating Smoothened.

The Hedgehog (Hh) signaling pathway plays important roles in developmental processes including pattern formation and tissue homeostasis. The seven-pass transmembrane receptor Smoothened (Smo) is the pivotal transducer in the pathway; it, and thus the pathway overall, is regulated by ubiquitin-mediated degradation, which occurs in the absence of Hh. In the presence of Hh, the ubiquitination levels of Smo are decreased, but the molecular basis for this outcome is not well understood. Here, we identify the deubiquitinase UCHL5 as a positive regulator of the Hh pathway. We provide both genetic and biochemical evidence that UCHL5 interacts with and deubiquitinates Smo, increasing stability and promoting accumulation at the cell membrane. Strikingly, we find that Hh enhances the interaction between UCHL5 and Smo, thereby stabilizing Smo. We also find that proteasome subunit RPN13, an activator of UCHL5, could enhance the effect of UCHL5 on Smo protein level. More importantly, we find that the mammalian counterpart of UCHL5, UCH37, plays the same role in the regulation of Hh signaling by modulating hSmo ubiquitination and stability. Our findings thus identify UCHL5/UCH37 as a critical regulator of Hh signaling and potential therapeutic target for cancers.