Inhibition of USP28 overcomes Cisplatin-resistance of squamous tumors by suppression of the Fanconi anemia pathway

USP28 promotes PARP inhibitor resistance by enhancing SOX9-mediated DNA damage repair in ovarian cancer

PARP inhibitor (PARPi) resistance presents a significant challenge in ovarian cancer treatment, necessitating the development of effective therapeutic strategies to overcome this resistance and improve patient outcomes. Our study demonstrated that elevated expression of SRY-box 9 (SOX9) contributes to olaparib resistance in ovarian cancer. Mechanistically, the deubiquitinating enzyme USP28 was identified as a novel interacting partner of SOX9. USP28 inhibited the ubiquitination and subsequent degradation of SOX9, which is mediated by the E3 ubiquitin ligase FBXW7 during olaparib treatment. ChIP-Seq analysis revealed that SOX9 binds to the promoters of key DNA damage repair (DDR) genes (SMARCA4, UIMC1, and SLX4), thereby regulating DDR processes in ovarian cancer. Additionally, USP28 promoted olaparib resistance by stabilizing SOX9 protein and enhancing DNA damage repair. Furthermore, the USP28 specific inhibitor AZ1 reduced SOX9 protein stability and increased the sensitivity of ovarian cancer cells to olaparib. In conclusion, targeted inhibition of USP28 promoted ubiquitination-mediated degradation of SOX9, thereby impairing DNA damage repair capabilities and sensitizing ovarian cancer cells to PARPi. These findings elucidate the underlying mechanisms of PARPi resistance in ovarian cancer and suggest the potential efficacy of combining USP28 inhibitors with PARPi to overcome this resistance.

Unraveling the role of deubiquitinating enzymes on cisplatin resistance in several cancers

The use of platinum-based drugs in cancer treatment is one of the most common methods in chemotherapy. Especially, cisplatin induces cell death by interrupting DNA synthesis by binding to the DNA bases, thereby leading to the apoptosis via multiple pathways. However, the major hurdle in chemotherapy is drug resistance. To overcome drug resistance, the ubiquitin-proteasome system (UPS) has emerged as a potential therapeutic target. The UPS is a pivotal signaling pathway that regulates the majority of cellular proteins by attaching ubiquitin to substrates, leading to proteasomal degradation. Conversely, deubiquitinating enzymes (DUBs) remove tagged ubiquitin from the substrate and inhibit degradation, thereby maintaining proteostasis. Recently, studies have been conducted to identify the substrates of DUBs and investigated the cellular mechanisms, and now the development of therapeutics using DUB inhibitors is in clinical trials. However, the mechanism of the DUB response to cisplatin remains still unclear. In this review, we summarize the research reported on the function of DUBs responding to cisplatin.

The deubiquitinase USP44 enhances cisplatin chemosensitivity through stabilizing STUB1 to promote LRPPRC degradation in neuroblastoma

BACKGROUND

Dysregulated deubiquitinating enzymes (DUBs) execute as intrinsic oncogenes or tumor suppressors and are involved in chemoresistance in cancers. However, the functions and exact molecular mechanisms remain largely unclear in neuroblastoma.

METHODS

Here, an R2 screening strategy based on the standard deviation values was used to identify the most important DUB, USP44, in neuroblastoma with stage 4. We validated the role of USP44 regulation upon cisplatin treatment in vitro and in vivo experiments, revealing the molecular mechanisms associated with USP44 regulation and cisplatin sensitivity in neuroblastoma.

RESULTS

We found that low USP44 expression was associated with an inferior prognosis in neuroblastoma patients. Overexpression of USP44 enhanced neuroblastoma cell sensitivity to cisplatin in vitro and in vivo. Mechanistically, USP44 recruited and stabilized the E3 ubiquitin ligase STUB1 by removing its K48-linked polyubiquitin chains at Lys30, and STUB1 further reinforced the K48-linked polyubiquitination of LRPPRC at Lys453 and promoted its protein degradation, thus enhancing the accumulation of mitochondrial reactive oxygen species (mROS), in turn facilitating neuroblastoma cell apoptosis and cisplatin sensitivity. Additionally, overexpression of LRPPRC reversed the promoting effect of USP44 on cell apoptosis in cisplatin-treated neuroblastoma cells.

CONCLUSIONS

Our findings demonstrate that the USP44-STUB1-LRPPRC axis plays a pivotal role in neuroblastoma chemoresistance and provides potential targets for neuroblastoma therapy and prognostication.

Lactylation: The metabolic accomplice shaping cancer's response to radiotherapy and immunotherapy

Protein lactylation, an emerging post-translational modification, is providing new insights into tumor biology and challenging our current understanding of cancer mechanisms. Our review illuminates the intricate roles of lactylation in carcinogenesis, tumor progression, and therapeutic responses, positioning it as a critical linchpin connecting metabolic reprogramming, epigenetic modulation, and treatment outcomes. We provide an in-depth analysis of lactylation's molecular mechanisms and its far-reaching impact on cell cycle regulation, immune evasion strategies, and therapeutic resistance within the complex tumor microenvironment. Notably, this review dissects the paradoxical nature of lactylation in cancer immunotherapy and radiotherapy. While heightened lactylation can foster immune suppression and radioresistance, strategically targeting lactylation cascades opens innovative avenues for amplifying the efficacy of current treatment paradigms. We critically evaluate lactylation's potential as a robust diagnostic and prognostic biomarker and explore frontier therapeutic approaches targeting lactylation. The synergistic integration of multi-omics data and artificial intelligence in lactylation research is catalyzing significant strides towards personalized cancer management. This review not only consolidates current knowledge but also charts a course for future investigations. Key research imperatives include deciphering tumor-specific lactylation signatures, optimizing synergistic strategies combining lactylation modulation with immune checkpoint inhibitors and radiotherapy, and comprehensively assessing the long-term physiological implications of lactylation intervention. As our understanding of lactylation's pivotal role in tumor biology continues to evolve, this burgeoning field promises to usher in transformative advancements in cancer diagnosis, treatment modalitie.

TIP60 enhances cisplatin resistance via regulating ΔNp63α acetylation in SCC

Non-melanoma skin cancer, including basal and squamous cell carcinoma, is the most common form of cancer worldwide, with approximately 5.4 million new cases diagnosed each year in the United States. While the chemotherapeutic drug cisplatin is often used to treat squamous cell carcinoma (SCC) patients, low response rates and disease recurrence are common. In this study, we show that TIP60 and ΔNp63α levels correlate with cisplatin resistance in SCC cell lines, suggesting that TIP60 contributes to the failure of platinum-based drugs in SCC by regulating the stability and transcriptional activity of ΔNp63α. Depletion of endogenous TIP60 or pharmacological inhibition of TIP60 led to a decrease in ΔNp63α protein and acetylation levels in multiple SCC cell lines. We showed that TIP60 upregulates ΔNp63α protein levels in cisplatin-resistant SCC cell lines by protecting it from cisplatin-mediated degradation and increasing its protein stability. Stable expression of TIP60 or ΔNp63α individually promoted resistance to cisplatin and reduced cell death, while loss of either TIP60 or ΔNp63α induced G2/M arrest, increased cell death, and sensitized cells to cisplatin. Moreover, pharmacological inhibition of TIP60 reduced acetylation of ΔNp63α and sensitized resistant cells to cisplatin. Taken together, our study indicates that TIP60-mediated stabilization of ΔNp63α increases cisplatin resistance and provides critical insights into the mechanisms by which ΔNp63α confers cisplatin resistance by promoting cell proliferation and inhibiting apoptosis. Furthermore, our data suggests that inhibition of TIP60 may be therapeutically advantageous in overcoming cisplatin resistance in SCC and other epithelial cancers.

USP10 drives cancer stemness and enables super-competitor signalling in colorectal cancer

The contribution of deubiquitylating enzymes (DUBs) to β-Catenin stabilization in intestinal stem cells and colorectal cancer (CRC) is poorly understood. Here, and by using an unbiassed screen, we discovered that the DUB USP10 stabilizes β-Catenin specifically in APC-truncated CRC in vitro and in vivo. Mechanistic studies, including in vitro binding together with computational modelling, revealed that USP10 binding to β-Catenin is mediated via the unstructured N-terminus of USP10 and is outcompeted by intact APC, favouring β-catenin degradation. However, in APC-truncated cancer cells USP10 binds to β-catenin, increasing its stability which is critical for maintaining an undifferentiated tumour identity. Elimination of USP10 reduces the expression of WNT and stem cell signatures and induces the expression of differentiation genes. Remarkably, silencing of USP10 in murine and patient-derived CRC organoids established that it is essential for NOTUM signalling and the APC super competitor-phenotype, reducing tumorigenic properties of APC-truncated CRC. These findings are clinically relevant as patient-derived organoids are highly dependent on USP10, and abundance of USP10 correlates with poorer prognosis of CRC patients. Our findings reveal, therefore, a role for USP10 in CRC cell identity, stemness, and tumorigenic growth by stabilising β-Catenin, leading to aberrant WNT signalling and degradation resistant tumours. Thus, USP10 emerges as a unique therapeutic target in APC truncated CRC.

Pathogenic proteotoxicity of cryptic splicing is alleviated by ubiquitination and ER-phagy

RNA splicing enables the functional adaptation of cells to changing contexts. Impaired splicing has been associated with diseases, including retinitis pigmentosa, but the underlying molecular mechanisms and cellular responses remain poorly understood. In this work, we report that deficiency of ubiquitin-specific protease 39 (USP39) in human cell lines, zebrafish larvae, and mice led to impaired spliceosome assembly and a cytotoxic splicing profile characterized by the use of cryptic 5' splice sites. Disruptive cryptic variants evaded messenger RNA (mRNA) surveillance pathways and were translated into misfolded proteins, which caused proteotoxic aggregates, endoplasmic reticulum (ER) stress, and, ultimately, cell death. The detrimental consequence of splicing-induced proteotoxicity could be mitigated by up-regulating the ubiquitin-proteasome system and selective autophagy. Our findings provide insight into the molecular pathogenesis of spliceosome-associated diseases.

The dimeric deubiquitinase USP28 integrates 53BP1 and MYC functions to limit DNA damage

DNA replication is a major source of endogenous DNA damage in tumor cells and a key target of cellular response to genotoxic stress. DNA replication can be deregulated by oncoproteins, such as transcription factor MYC, aberrantly activated in many human cancers. MYC is stringently regulated by the ubiquitin system - for example, ubiquitination controls recruitment of the elongation factor PAF1c, instrumental in MYC activity. Curiously, a key MYC-targeting deubiquitinase USP28 also controls cellular response to DNA damage via the mediator protein 53BP1. USP28 forms stable dimers, but the biological role of USP28 dimerization is unknown. We show here that dimerization limits USP28 activity and restricts recruitment of PAF1c by MYC. Expression of monomeric USP28 stabilizes MYC and promotes PAF1c recruitment, leading to ectopic DNA synthesis and replication-associated DNA damage. USP28 dimerization is stimulated by 53BP1, which selectively binds USP28 dimers. Genotoxic stress diminishes 53BP1-USP28 interaction, promotes disassembly of USP28 dimers and stimulates PAF1c recruitment by MYC. This triggers firing of DNA replication origins during early response to genotoxins and exacerbates DNA damage. We propose that dimerization of USP28 prevents ectopic DNA replication at transcriptionally active chromatin to maintain genome stability.

USP28 promotes tumorigenesis and cisplatin resistance by deubiquitinating MAST1 protein in cancer cells

Cisplatin is a chemotherapy drug that causes a plethora of DNA lesions and inhibits DNA transcription and replication, resulting in the induction of apoptosis in cancer cells. However, over time, patients develop resistance to cisplatin due to repeated treatment and thus the treatment efficacy is limited. Therefore, identifying an alternative therapeutic strategy combining cisplatin treatment along with targeting factors that drive cisplatin resistance is needed. CRISPR/Cas9 system-based genome-wide screening for the deubiquitinating enzyme (DUB) subfamily identified USP28 as a potential DUB that governs cisplatin resistance. USP28 regulates the protein level of microtubule-associated serine/threonine kinase 1 (MAST1), a common kinase whose expression is elevated in several cisplatin-resistant cancer cells. The expression level and protein turnover of MAST1 is a major factor driving cisplatin resistance in many cancer types. Here we report that the USP28 interacts and extends the half-life of MAST1 protein by its deubiquitinating activity. The expression pattern of USP28 and MAST1 showed a positive correlation across a panel of tested cancer cell lines and human clinical tissues. Additionally, CRISPR/Cas9-mediated gene knockout of USP28 in A549 and NCI-H1299 cells blocked MAST1-driven cisplatin resistance, resulting in suppressed cell proliferation, colony formation ability, migration and invasion in vitro. Finally, loss of USP28 destabilized MAST1 protein and attenuated tumor growth by sensitizing cells to cisplatin treatment in mouse xenograft model. We envision that targeting the USP28-MAST1 axis along with cisplatin treatment might be an alternative therapeutic strategy to overcome cisplatin resistance in cancer patients.

Otilonium Bromide acts as a selective USP28 inhibitor and exhibits cytotoxic activity against multiple human cancer cell lines

USP28 contributes to tumorigenesis through modulating the lifespan of oncogenic factors such as c-Myc and ΔNp63, and it has been identified as a potential target for anti-cancer drug development. Currently, although quite a number of USP28 inhibitors have been developed, they all are still in preclinical research stage. Besides, none of them exhibits satisfying inhibition selectivity against USP28 over its closest homologue USP25. Here in this manuscript, a high-throughput screening aiming to discover USP28 inhibitors with novel scaffold and enhanced inhibition selectivity were conducted. After the primary screening and the second round of validation, Otilonium Bromide, an approved drug for treating irritable bowel syndrome, was identified to inhibit USP28's activity with the IC50 value at 6.90 ± 0.90 μM. Besides, the drug exhibits a 3-4 folds inhibition selectivity against USP28 over USP25. According to the enzymatic kinetics analysis data and the hydrogen-deuterium exchange mass spectrometry results, Otilonium Bromide could bind to the allosteric pocket of USP28 and inhibit its activity in a reversible and non-competitive mode. The following performed cell-based assays revealed that the drug could cause cytotoxicity against human colorectal cancer cells and lung squamous carcinoma cells potentially through down-regulating USP28's oncogenic substrates c-Myc and/or ΔNp63. Meanwhile, since Otilonium Bromide has been found to preferentially distribute to gastrointestinal tissues, we then evaluated its potential in the combination treatment of colorectal cancer cells with Regorafenib, which is an approved drug for colorectal cancer therapy. As expected, Otilonium Bromide could significantly enhance the sensitivity of colorectal cancer cells to Regorafenib.

Comprehensive prognostic and immunological analysis of Ubiquitin Specific Peptidase 28 in pan-cancers and identification of its role in hepatocellular carcinoma cell lines

BACKGROUND

Ubiquitin Specific Peptidase 28 (USP28), as a member of the DUBs family, has been reported to regulate the occurrence and development of some tumors, but its oncogenic role in tumor immunity is still unknown.

METHODS

The comprehensive view of USP28 expression in tumor and normal samples was obtained from public databases, including The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Cancer Cell Line Encyclopedia (CCLE). We analyzed the genomic alterations of USP28 in various cancers using the cBioPortal dataset. Besides, gene set enrichment analysis was used to analyze the associated cancer hallmarks with USP28 expression, and TIMER2.0 was taken to investigate the immune cell infiltrations related to the USP28 level.

RESULTS

USP28 is highly expressed in most tumors and has prognostic value across various cancer types. Moreover, a significant correlation exists between USP28 and immune regulators, clinical staging, checkpoint inhibitor response, MSI, TMB, CNV, MMR defects, and DNA methylation. Additionally, USP28 expression is strongly associated with the infiltration levels of neutrophils and NK cells in most tumor types. One of the most significant findings of our study was that USP28 could serve as a significant predictor of anti-CTLA4 therapy response in melanoma patients. Additionally, our molecular biology experiments validated that the knockdown of USP28 substantially reduced the proliferative and invasive abilities of the HCC cell lines.

CONCLUSIONS

Our study suggests that USP28 could potentially serve as a biomarker for cancer immunologic infiltration and poor prognosis, with potential applications in developing novel cancer treatment strategies.

USP28 controls SREBP2 and the mevalonate pathway to drive tumour growth in squamous cancer

SREBP2 is a master regulator of the mevalonate pathway (MVP), a biosynthetic process that drives the synthesis of dolichol, heme A, ubiquinone and cholesterol and also provides substrates for protein prenylation. Here, we identify SREBP2 as a novel substrate for USP28, a deubiquitinating enzyme that is frequently upregulated in squamous cancers. Our results show that silencing of USP28 reduces expression of MVP enzymes and lowers metabolic flux into this pathway. We also show that USP28 binds to mature SREBP2, leading to its deubiquitination and stabilisation. USP28 depletion rendered cancer cells highly sensitive to MVP inhibition by statins, which was rescued by the addition of geranyl-geranyl pyrophosphate. Analysis of human tissue microarrays revealed elevated expression of USP28, SREBP2 and MVP enzymes in lung squamous cell carcinoma (LSCC) compared to lung adenocarcinoma (LADC). Moreover, CRISPR/Cas-mediated deletion of SREBP2 selectively attenuated tumour growth in a KRas/p53/LKB1 mutant mouse model of lung cancer. Finally, we demonstrate that statins synergise with a dual USP28/25 inhibitor to reduce viability of SCC cells. Our findings suggest that combinatorial targeting of MVP and USP28 could be a therapeutic strategy for the treatment of squamous cell carcinomas.

Structure-based discovery of potent USP28 inhibitors derived from Vismodegib

Ubiquitin-specific proteases (USPs) 28 is overexpressed in multiple types of cancers. The development of potent USP28 inhibitors is still in primitive stage. We previously reported our discovery of Vismodegib as a USP28 inhibitor by screening a commercially available drug library. Herein, we report our efforts to solve the cocrystal structure of Vismodegib bound to USP28 for the first time and subsequent structure-based optimization leading to a series of Vismodegib derivatives as potent USP28 inhibitors. Based on the cocrystal structure, elaborative SARs exploration was carried out to afford much more potent USP28 inhibitors than Vismodegib. The representative compounds 9l, 9o and 9p bearing high potency on USP28 showed high selectivity over USP2, USP7, USP8, USP9x, UCHL3 and UCHL5. The detailed cellular assay suggested that compounds 9l, 9o and 9p could cause cytotoxicity in both human colorectal cancer and lung squamous carcinoma cells and significantly enhance the sensitivity of colorectal cancer cells to Regorafenib. Further immunoblotting analysis indicated that compounds 9l, 9o and 9p could dose-dependently down-regulate the cellular level of c-Myc through ubiquitin-proteasome system and anti-cancer effects could mainly be attributed to their inhibition on USP28 but not involving the Hedgehog-Smoothened pathway. Thus, our work provided a series of novel and potent USP28 inhibitors derived from Vismodegib and may contribute to the development of USP28 inhibitors.

Deubiquitylase PSMD14 inhibits autophagy to promote ovarian cancer progression via stabilization of LRPPRC

Autophagy is a key cellular process, which exists in many tumors and plays dual roles in tumor promotion and suppression. However, the role and mechanism of aberrant autophagy in ovarian cancer remains unclear. Ubiquitin-proteasome pathway is the most important pathway for specific protein degradation. Deubiquitinases (DUBs) have crucial roles in all the stages of tumorigenesis and progression. Herein, we explore the DUBs which contribute to aberrant autophagy in ovarian cancer. TCGA data analysis shows that the autophagy level is suppressed, and the selective autophagy receptor SQSTM1/p62 is abnormally high expressed in ovarian cancer. We screen and identify that the deubiquitinase PSMD14 negatively regulates autophagy level. Functional studies show that increased PSMD14 expression remarkably enhances ovarian cancer cells malignancy, whereas knockdown of PSMD14 has the opposite effect. Furthermore, in vivo assays show that knockdown of PSMD14 inhibits the growth, lung and abdominal metastasis of ovarian cancer. Mechanistically, PSMD14 directly interacts with LRPPRC and inhibits its ubiquitination, thereby inhibiting autophagy through LRPPRC/Beclin1-Bcl-2/SQSTM1 signaling pathway. Next, we demonstrate that PSMD14 is upregulated in ovarian cancer and high expression of PSMD14 positively correlates with LRPPRC. Taken together, we clarify the role of autophagy in regulating the ovarian cancer phenotype and provide insights into regulatory mechanism of autophagy in ovarian cancer.

Identification of the deubiquitinase USP28 as a novel molecular therapeutic target of ovarian cancer

Ubiquitin specific proteinase 28 (USP28) is a member of the deubiquitylating enzymes, which are mainly involved in cell cycle, apoptosis and DNA damage repair. Although USP28 has been found to be upregulated in some tumors, its role in ovarian cancer (OV) remains unclear. Here we show that USP28 was highly expressed in OV samples compared with normal ovarian tissue, and OV patients with higher USP28 levels had a worse prognosis. We found that the abnormal expression of USP28 mRNA in OV was related to the activation of β-catenin signaling pathway, and USP28 was a transcriptional target gene of the β-catenin/YAP1/TBX5 complex. In addition, genetic ablation or pharmacological inhibition of USP28 impaired the proliferation ability of OV cells in vitro and in vivo. In conclusion, our findings show that β-catenin/YAP1/TBX5-mediated aberrant expression of USP28 promotes the malignant phenotype of OV, suggesting that USP28 may be a therapeutic target for OV.

The dual role of p63 in cancer

The p53 family is made up of three transcription factors: p53, p63, and p73. These proteins are well-known regulators of cell function and play a crucial role in controlling various processes related to cancer progression, including cell division, proliferation, genomic stability, cell cycle arrest, senescence, and apoptosis. In response to extra- or intracellular stress or oncogenic stimulation, all members of the p53 family are mutated in structure or altered in expression levels to affect the signaling network, coordinating many other pivotal cellular processes. P63 exists as two main isoforms (TAp63 and ΔNp63) that have been contrastingly discovered; the TA and ΔN isoforms exhibit distinguished properties by promoting or inhibiting cancer progression. As such, p63 isoforms comprise a fully mysterious and challenging regulatory pathway. Recent studies have revealed the intricate role of p63 in regulating the DNA damage response (DDR) and its impact on diverse cellular processes. In this review, we will highlight the significance of how p63 isoforms respond to DNA damage and cancer stem cells, as well as the dual role of TAp63 and ΔNp63 in cancer.

Deep transfer learning of cancer drug responses by integrating bulk and single-cell RNA-seq data

Drug screening data from massive bulk gene expression databases can be analyzed to determine the optimal clinical application of cancer drugs. The growing amount of single-cell RNA sequencing (scRNA-seq) data also provides insights into improving therapeutic effectiveness by helping to study the heterogeneity of drug responses for cancer cell subpopulations. Developing computational approaches to predict and interpret cancer drug response in single-cell data collected from clinical samples can be very useful. We propose scDEAL, a deep transfer learning framework for cancer drug response prediction at the single-cell level by integrating large-scale bulk cell-line data. The highlight in scDEAL involves harmonizing drug-related bulk RNA-seq data with scRNA-seq data and transferring the model trained on bulk RNA-seq data to predict drug responses in scRNA-seq. Another feature of scDEAL is the integrated gradient feature interpretation to infer the signature genes of drug resistance mechanisms. We benchmark scDEAL on six scRNA-seq datasets and demonstrate its model interpretability via three case studies focusing on drug response label prediction, gene signature identification, and pseudotime analysis. We believe that scDEAL could help study cell reprogramming, drug selection, and repurposing for improving therapeutic efficacy.

Signaling pathways and targeted therapies in lung squamous cell carcinoma: mechanisms and clinical trials

Lung cancer is the leading cause of cancer-related death across the world. Unlike lung adenocarcinoma, patients with lung squamous cell carcinoma (LSCC) have not benefitted from targeted therapies. Although immunotherapy has significantly improved cancer patients' outcomes, the relatively low response rate and severe adverse events hinder the clinical application of this promising treatment in LSCC. Therefore, it is of vital importance to have a better understanding of the mechanisms underlying the pathogenesis of LSCC as well as the inner connection among different signaling pathways, which will surely provide opportunities for more effective therapeutic interventions for LSCC. In this review, new insights were given about classical signaling pathways which have been proved in other cancer types but not in LSCC, including PI3K signaling pathway, VEGF/VEGFR signaling, and CDK4/6 pathway. Other signaling pathways which may have therapeutic potentials in LSCC were also discussed, including the FGFR1 pathway, EGFR pathway, and KEAP1/NRF2 pathway. Next, chromosome 3q, which harbors two key squamous differentiation markers SOX2 and TP63 is discussed as well as its related potential therapeutic targets. We also provided some progress of LSCC in epigenetic therapies and immune checkpoints blockade (ICB) therapies. Subsequently, we outlined some combination strategies of ICB therapies and other targeted therapies. Finally, prospects and challenges were given related to the exploration and application of novel therapeutic strategies for LSCC.

RNF4~RGMb~BMP6 axis required for osteogenic differentiation and cancer cell survival

Molecular understanding of osteogenic differentiation (OD) of human bone marrow-derived mesenchymal stem cells (hBMSCs) is important for regenerative medicine and has direct implications for cancer. We report that the RNF4 ubiquitin ligase is essential for OD of hBMSCs, and that RNF4-deficient hBMSCs remain as stalled progenitors. Remarkably, incubation of RNF4-deficient hBMSCs in conditioned media of differentiating hBMSCs restored OD. Transcriptional analysis of RNF4-dependent gene signatures identified two secreted factors that act downstream of RNF4 promoting OD: (1) BMP6 and (2) the BMP6 co-receptor, RGMb (Dragon). Indeed, knockdown of either RGMb or BMP6 in hBMSCs halted OD, while only the combined co-addition of purified RGMb and BMP6 proteins to RNF4-deficient hBMSCs fully restored OD. Moreover, we found that the RNF4-RGMb-BMP6 axis is essential for survival and tumorigenicity of osteosarcoma and therapy-resistant melanoma cells. Importantly, patient-derived sarcomas such as osteosarcoma, Ewing sarcoma, liposarcomas, and leiomyosarcomas exhibit high levels of RNF4 and BMP6, which are associated with reduced patient survival. Overall, we discovered that the RNF4~BMP6~RGMb axis is required for both OD and tumorigenesis.

USP28 Deubiquitinates TCF7L2 to Govern the Action of Wnt Signaling Pathway in Hepatic Carcinoma

Overexpression of ubiquitin‐specific protease 28 (USP28) is found in hepatic carcinoma. It is unclear whether the deubiquitinase plays a role in hepatocarcinogenesis. Deregulation of the Wnt signaling pathway is frequently associated with liver cancer. Transcription factor 7‐like 2 (TCF7L2) is an important downstream transcription factor of the Wnt/β‐catenin signaling pathway, but the mechanisms by which TCF7L2 itself is regulated have not yet been revealed. Here, we report that USP28 promotes the activity of the Wnt signaling pathway through maintaining the stability of TCF7L2. We further show that FBXW7 is the E3 ubiquitin ligase for TCF7L2. By regulating the levels of TCF7L2, USP28 modulates the Wnt/β‐catenin signaling in liver cancer and USP28 depletion or inhibition by a small molecule inhibitor leads to a halt of growth in liver cancer cells. These results suggest that USP28 could be a potential therapeutic target for liver cancer.

Can Cisplatin Therapy Be Improved? Pathways That Can Be Targeted

Cisplatin (cis-diamminedichloroplatinum (II)) is the oldest known chemotherapeutic agent. Since the identification of its anti-tumour activity, it earned a remarkable place as a treatment of choice for several cancer types. It remains effective against testicular, bladder, lung, head and neck, ovarian, and other cancers. Cisplatin treatment triggers different cellular responses. However, it exerts its cytotoxic effects by generating inter-strand and intra-strand crosslinks in DNA. Tumour cells often develop tolerance mechanisms by effectively repairing cisplatin-induced DNA lesions or tolerate the damage by adopting translesion DNA synthesis. Cisplatin-associated nephrotoxicity is also a huge challenge for effective therapy. Several preclinical and clinical studies attempted to understand the major limitations associated with cisplatin therapy, and so far, there is no definitive solution. As such, a more comprehensive molecular and genetic profiling of patients is needed to identify those individuals that can benefit from platinum therapy. Additionally, the treatment regimen can be improved by combining cisplatin with certain molecular targeted therapies to achieve a balance between tumour toxicity and tolerance mechanisms. In this review, we discuss the importance of various biological processes that contribute to the resistance of cisplatin and its derivatives. We aim to highlight the processes that can be modulated to suppress cisplatin resistance and provide an insight into the role of uptake transporters in enhancing drug efficacy.

USP28 enables oncogenic transformation of respiratory cells and its inhibition potentiates molecular therapy targeting mutant EGFR, BRAF and PI3K

Oncogenic transformation of lung epithelial cells is a multistep process, frequently starting with the inactivation of tumour suppressors and subsequent development of activating mutations in proto‐oncogenes, such as members of the PI3K or MAPK families. Cells undergoing transformation have to adjust to changes, including altered metabolic requirements. This is achieved, in part, by modulating the protein abundance of transcription factors. Here, we report that the ubiquitin carboxyl‐terminal hydrolase 28 (USP28) enables oncogenic reprogramming by regulating the protein abundance of proto‐oncogenes such as c‐JUN, c‐MYC, NOTCH and ∆NP63 at early stages of malignant transformation. USP28 levels are increased in cancer compared with in normal cells due to a feed‐forward loop, driven by increased amounts of oncogenic transcription factors such as c‐MYC and c‐JUN. Irrespective of oncogenic driver, interference with USP28 abundance or activity suppresses growth and survival of transformed lung cells. Furthermore, inhibition of USP28 via a small‐molecule inhibitor resets the proteome of transformed cells towards a ‘premalignant’ state, and its inhibition synergizes with clinically established compounds used to target EGFR^L858R‐, BRAF^V600E‐ or PI3K^H1047R‐driven tumour cells. Targeting USP28 protein abundance at an early stage via inhibition of its activity is therefore a feasible strategy for the treatment of early‐stage lung tumours, and the observed synergism with current standard‐of‐care inhibitors holds the potential for improved targeting of established tumours.

Identifying pathways regulating the oncogenic p53 family member ΔNp63 provides therapeutic avenues for squamous cell carcinoma

Background

ΔNp63 overexpression is a common event in squamous cell carcinoma (SCC) that contributes to tumorigenesis, making ΔNp63 a potential target for therapy.

Methods

We created inducible TP63-shRNA cells to study the effects of p63-depletion in SCC cell lines and non-malignant HaCaT keratinocytes. DNA damaging agents, growth factors, signaling pathway inhibitors, histone deacetylase inhibitors, and metabolism-modifying drugs were also investigated for their ability to influence ΔNp63 protein and mRNA levels.

Results

HaCaT keratinocytes, FaDu and SCC-25 cells express high levels of ΔNp63. HaCaT and FaDu inducible TP63-shRNA cells showed reduced proliferation after p63 depletion, with greater effects on FaDu than HaCaT cells, compatible with oncogene addiction in SCC. Genotoxic insults and histone deacetylase inhibitors variably reduced ΔNp63 levels in keratinocytes and SCC cells. Growth factors that regulate proliferation/survival of squamous cells (IGF-1, EGF, amphiregulin, KGF, and HGF) and PI3K, mTOR, MAPK/ERK or EGFR inhibitors showed lesser and inconsistent effects, with dual inhibition of PI3K and mTOR or EGFR inhibition selectively reducing ΔNp63 levels in HaCaT cells. In contrast, the antihyperlipidemic drug lovastatin selectively increased ΔNp63 in HaCaT cells.

Conclusions

These data confirm that ΔNp63-positive SCC cells require p63 for continued growth and provide proof of concept that p63 reduction is a therapeutic option for these tumors. Investigations of ΔNp63 regulation identified agent-specific and cell-specific pathways. In particular, dual inhibition of the PI3K and mTOR pathways reduced ΔNp63 more effectively than single pathway inhibition, and broad-spectrum histone deacetylase inhibitors showed a time-dependent biphasic response, with high level downregulation at the transcriptional level within 24 h. In addition to furthering our understanding of ΔNp63 regulation in squamous cells, these data identify novel drug combinations that may be useful for p63-based therapy of SCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00323-x.