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.

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.

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.

The structure and regulation of the E3 ubiquitin ligase HUWE1 and its biological functions in cancer.

E3 ligases are a class of critical enzymes that can catalyse the transfer of ubiquitin (Ub) from an E2 enzyme to the substrate and are essential to cellular processes. The E3 ligase HUWE1 (also known as ARF-BP1, HECTH9, HSPC272, Ib772, LASU1, MULE, URE-B1, UREB1, and HECT, UBA and WWE domain-containing E3 ubiquitin protein ligase 1) is encoded by the huwe1 gene. HUWE1 is a key regulator of the DNA damage response, transcription, autophagy, apoptosis and metabolism in a variety of cancers. Due to its pivotal role in conferring substrate specificity, HUWE1 has attracted enormous attention as a promising anticancer drug target. In this review, we indicate the specific molecular structure of HUWE1 and its role in various cellular signalling pathways and highlight new insights into HUWE1 in cancer. Finally, we discuss outstanding questions regarding HUWE1 in oncology and highlight its limitations in drug development and clinical guidance to better define the role of HUWE1 in multiple cancers.