Inhibition of deubiquitinase USP28 attenuates cyst growth in autosomal dominant polycystic kidney disease

USP28 knockdown and small molecule inhibitors promote KRT1 destabilization and sensitize hepatocellular carcinoma cells to sorafenib

BACKGROUND

Hepatocellular carcinoma (HCC) is a significant malignant tumor that is typically diagnosed late and has a poor prognosis. USP28 (Ubiquitin-specific protease 28), a deubiquitinating enzyme within the ubiquitin-specific proteases (USPs) family, plays a pivotal role in various biological processes, especially in cancer progression. However, its functions and molecular mechanisms in HCC are still unknown.

METHODS

We first analyzed the expression level of USP28 in HCC tissues relative to normal tissues using TCGA database. This was further validated by qRT-PCR and Western Blot. To investigate the function of USP28 in HCC, CCK-8 assay, clone formation assay and Transwell assay were performed in control and USP28 knockdown or overexpressed HCC cells. To explore potential downstream targets of USP28, we used IP-MS analysis. The interaction between USP28 and KRT1 was confirmed by immunoprecipitation and immunofluorescence staining. Finally, we evaluated the in vivo effects of USP28 on HCC growth and metastasis using a ectopic tumor-bearing mouse model.

RESULTS

The expression of USP28 in HCC tissues was significantly higher than that in normal tissues, and its high expression was associated with poor prognosis. Functional experiments showed that down-regulation of USP28 expression effectively inhibited the proliferation, migration and invasion of HCC cells, while overexpression of USP28 produced the opposite effect. Mechanistic investigations demonstrated that USP28 interacted with KRT1 and exerted deubiquitination on KRT1, thereby maintaining the stability of KRT1. Further studies revealed that USP28 knockdown resulted in decreased IFITM3 expression, which inhibited HCC cell proliferation. In addition, USP28 knockdown combined with sorafenib inhibited tumor growth and metastasis in tumor xenograft mice model.

CONCLUSIONS

Our study confirmed the carcinogenic effects of USP28 by stabilizing KRT1 expression and promoting IFITM3. USP28 small molecule inhibitors can inhibit the proliferation of hepatocellular carcinoma cells and enhance the sensitivity of hepatocellular carcinoma cell lines to sorafenib. This provides a theoretical basis for USP28 to be a new clinical method to alleviate sorafenib resistance.

Design of Selective BRD4 Inhibitors for the Treatment of Autosomal Dominant Polycystic Kidney Disease

Epigenetic modulation plays a pivotal role in restraining tumor progression by governing gene expression and protein function. Autosomal dominant polycystic kidney disease (ADPKD), characterized by neoplastic-like progression, can be managed by inhibiting cyst expansion. Of note, the epigenetic regulator BRD4 has been implicated in ADPKD's development. Our prior research unveiled a class of (pyrazol-3-yl) pyrimidin-4-amine compounds as potent BRD4 inhibitors with additional kinase inhibition, which might induce unwanted biological activities. To address this, this study focused on creating selective BRD4 inhibitors through structure-guided design, minimizing off-target kinase interactions. Specifically, compound 23 emerged as an efficacious and selective BRD4 inhibitor in cellular and embryonic kidney models of ADPKD, along with encouraging outcomes in murine models. Collectively, these results highlight the therapeutic potential of targeted BRD4 inhibition as a safe and efficacious strategy for managing ADPKD.

OTUD6A in tubular epithelial cells mediates angiotensin II-induced kidney injury by targeting STAT3

Kidney fibrosis is a prominent pathological feature of hypertensive kidney diseases (HKD). Recent studies have highlighted the role of ubiquitinating/deubiquitinating protein modification in kidney pathophysiology. Ovarian tumor domain-containing protein 6 A (OTUD6A) is a deubiquitinating enzyme involved in tumor progression. However, its role in kidney pathophysiology remains elusive. We aimed to investigate the role and underlying mechanism of OTUD6A during kidney fibrosis in HKD. The results revealed higher OTUD6A expression in kidney tissues of nephropathy patients and mice with chronic angiotensin II (Ang II) administration than that from the control ones. OTUD6A was mainly located in tubular epithelial cells. Moreover, OTUD6A deficiency significantly protected mice against Ang II-induced kidney dysfunction and fibrosis. Also, knocking OTUD6A down suppressed Ang II-induced fibrosis in cultured tubular epithelial cells, whereas overexpression of OTUD6A enhanced fibrogenic responses. Mechanistically, OTUD6A bounded to signal transducer and activator of transcription 3 (STAT3) and removed K63-linked-ubiquitin chains to promote STAT3 phosphorylation at tyrosine 705 position and nuclear translocation, which then induced profibrotic gene transcription in epithelial cells. These studies identified STAT3 as a direct substrate of OTUD6A and highlighted the pivotal role of OTUD6A in Ang II-induced kidney injury, indicating OTUD6A as a potential therapeutic target for HKD.NEW & NOTEWORTHY Ovarian tumor domain-containing protein 6 A (OTUD6A) knockout mice are protected against angiotensin II-induced kidney dysfunction and fibrosis. OTUD6A promotes pathological kidney remodeling and dysfunction by deubiquitinating signal transducer and activator of transcription 3 (STAT3). OTUD6A binds to and removes K63-linked-ubiquitin chains of STAT3 to promote its phosphorylation and activation, and subsequently enhances kidney fibrosis.

Novel insights into STAT3 in renal diseases

Signal transducer and activator of transcription 3 (STAT3) is a cell-signal transcription factor that has attracted considerable attention in recent years. The stimulation of cytokines and growth factors can result in the transcription of a wide range of genes that are crucial for several cellular biological processes involved in pro- and anti-inflammatory responses. STAT3 has attracted considerable interest as a result of a recent upsurge in study because of their role in directing the innate immune response and sustaining inflammatory pathways, which is a key feature in the pathogenesis of many diseases, including renal disorders. Several pathological conditions which may involve STAT3 include diabetic nephropathy, acute kidney injury, lupus nephritis, polycystic kidney disease, and renal cell carcinoma. STAT3 is expressed in various renal tissues under these pathological conditions. To better understand the role of STAT3 in the kidney and provide a theoretical foundation for STAT3-targeted therapy for renal disorders, this review covers the current work on the activities of STAT3 and its mechanisms in the pathophysiological processes of various types of renal diseases.