Interference of Skp2 effectively inhibits the development and metastasis of colon carcinoma

Short interfering RNA in colorectal cancer: is it wise to shoot the messenger?

Colorectal cancer (CRC) is the third most common cancer and the leading cause of gastrointestinal cancer death. 90% of people diagnosed with colorectal cancer are over the age of 50; nevertheless, the illness is more aggressive among those detected at a younger age. Chemotherapy-based treatment has several adverse effects on both normal and malignant cells. The primary signaling pathways implicated in the advancement of CRC include hedgehog (Hh), janus kinase and signal transducer and activator of transcription (JAK/STAT), Wingless-related integration site (Wnt)/β-catenin, transforming growth factor-β (TNF-β), epidermal growth factor receptor (EGFR)/Mitogen-activated protein kinases (MAPK), phosphoinositide 3-kinase (PI3K), nuclear factor kappa B (NF-κB), and Notch. Loss of heterozygosity in tumor suppressor genes like adenomatous polyposis coli, as well as mutation or deletion of genes like p53 and Kirsten rat sarcoma viral oncogene (KRAS), are all responsible for the occurrence of CRC. Novel therapeutic targets linked to these signal-transduction cascades have been identified as a consequence of advances in small interfering RNA (siRNA) treatments. This study focuses on many innovative siRNA therapies and methodologies for delivering siRNA therapeutics to the malignant site safely and effectively for the treatment of CRC. Treatment of CRC using siRNA-associated nanoparticles (NPs) may inhibit the activity of oncogenes and MDR-related genes by targeting a range of signaling mechanisms. This study summarizes several siRNAs targeting signaling molecules, as well as the therapeutic approaches that might be employed to treat CRC in the future.

Small-molecule compounds inhibiting S-phase kinase-associated protein 2: A review

S-phase kinase-associated protein 2 (Skp2) is a substrate-specific adaptor in Skp1-CUL1-ROC1-F-box E3 ubiquitin ligases and widely regarded as an oncogene. Therefore, Skp2 has remained as an active anticancer research topic since its discovery. Accordingly, the structure of Skp2 has been solved and numerous Skp2 inhibiting compounds have been identified. In this review, we would describe the structural features of Skp2, introduce the ubiquitination function of SCF^Skp2, and summarize the diverse natural and synthetic Skp2 inhibiting compounds reported to date. The IC₅₀ data of the Skp2 inhibitors or inhibiting compounds in various kinds of tumors at cellular levels implied that the cancer type, stage and pathological mechanisms should be taken into consideration when selecting Skp2-inhibiting compound for cancer treatment.

The CK1δ/ε-AES axis regulates tumorigenesis and metastasis in colorectal cancer

Background: Amino-terminal enhancer of split (AES) has been identified as a tumor and metastasis suppressor in some cancers including colorectal cancer (CRC), but very little is known about the regulation of AES expression.

Methods: Bioinformatics analysis was used to investigate the expression patterns of AES, CK1δ and CK1ε. The co-immunoprecipitation, GST pull-down, Western Blot, real-time PCR and immunohistochemistry were performed to study the mechanism underlying the regulation of AES expression by CK1δ/ε. The biological function was assessed by in vitro colony formation, transwell, sphere formation, tumor organoids, in vivo tumor metastasis model and patient-derived colorectal tumor xenografts (PDTX) model.

Results: A strong inverse relationship was observed between the expression of AES and the expression of CK1δ/ε. Mechanically, AES could interact with CK1δ/ε and SKP2 using its Q domain. SKP2 mediated the ubiquitination and degradation of AES in a CK1δ/ε-dependent manner. CK1δ/ε phosphorylated AES at Ser121 and accelerated the SKP2-mediated ubiquitination and degradation of AES. In colon cancer cells, CK1δ/ε antagonized the effect of wild-type AES but not that of its mutant (S121A) on Wnt and Notch signaling, leading to an increase in the expression of Wnt target genes and Notch target genes. By downregulating the expression of AES, CK1δ/ε enhanced anchorage-independent growth, migration, invasion and sphere formation in colon cancer cells. CK1δ/ε also promoted the growth of APC^min/+ colorectal tumor organoids and liver metastasis in colon cancer mouse models through the regulation of AES degradation. Furthermore, CK1 inhibitor SR3029 treatment suppressed tumor growth via stabilizing AES in APC^min/+ colorectal tumor organoids and patient-derived colorectal tumor xenografts (PDTX).

Conclusions: Our results revealed that the CK1δ/ε-AES axis is important for CRC tumorigenesis and metastasis, and targeted inhibition of this axis may be a potential therapeutic strategy for CRC.

Differential Expression of HER2 and SKP2 in Benign and Malignant Colorectal Lesions

BACKGROUND

Colorectal cancer (CRC) is the fourth most common cancer worldwide. Both HER2 and SKP2 have a carcinogenic role in CRC making them attractive targets for tailored treatment. This work aims to correlate HER2 and SKP2 protein expression as well as HER2 gene amplification with clinicopathological parameters aiming at identifying potential candidates for targeted therapy.

METHODS

This Study was conducted on 127 paraffin-embedded tissue samples of different colorectal lesions [controls, chronic colitis, ulcerative colitis (UC), hyperplastic polyps (HPs), adenomas and CRCs] to investigate HER2 and SKP2 expression by immunohistochemistry (IHC), Selected CRC cases [equivocal (2+) and positive (3+) by IHC] were further evaluated by ISH (CISH and SISH ) to assess HER2 gene amplification.

RESULTS

Chronic colitis, UC, HPs and adenomas were HER2-negative. HER2 positivity (scores 2+ and 3+) was found only in15% of CRCs. Both SISH and CISH showed the same results with high concordance as 66.7% of equivocal and 100% of positive cases showed amplification of HER2 gene. SKP2 positivity was detected in 26.7% and 45% of adenomas and CRCs respectively, while other studied groups were negative. A significant correlation was noted between HER2 and SKP2 expression.

CONCLUSION

A small percent of CRCs exhibited HER2 gene amplification, which would be potential candidates for anti HER2 therapy whereas IHC could be a primary screening test for patient selection. A potential carcinogenic role of SKP2 was suggested by the findings that SKP2 expression was undetectable in normal colonic mucosa but significantly increases from adenoma to carcinoma, hoping adenoma patients to get benefit from targeted therapy.
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AMPKα2 deficiency exacerbates hypoxia-induced pulmonary hypertension by promoting pulmonary arterial smooth muscle cell proliferation

Increased evidence indicates that adenosine monophosphate-activated protein kinase (AMPK) plays a vital role in vascular homeostasis, especially under hypoxia, and protects against the progression of pulmonary hypertension (PH). However, the role of AMPK in the pathogenesis of PH remains to be clarified. In the present study, we confirmed that a loss of AMPKα2 exacerbated the development of PH by using hypoxia-induced PH model in AMPKα2 ^-/- mice. After a 4-week period of hypoxic exposure, AMPKα2 ^-/- mice exhibited more severe pulmonary vascular remodeling and pulmonary vascular smooth muscle cell (SMC) proliferation when compared with wild type (WT) mice. In vitro, AMPKα2 knockdown promoted the proliferation of pulmonary arterial smooth muscle cells (PASMCs) under hypoxia. This phenomenon was accompanied by upregulated Skp2 and downregulated p27^kip1 expression and was abolished by rapamycin, an inhibitor of mTOR. These results indicate that AMPKα2 deficiency exacerbates hypoxia-induced PH by promoting PASMC proliferation via the mTOR/Skp2/p27^kip1 signaling axis. Therefore, enhanced AMPKα2 activity might underlie a novel therapeutic strategy for the management of PH.

Skp2 in the ubiquitin-proteasome system: A comprehensive review

The ubiquitin-proteasome system (UPS) is a complex process that regulates protein stability and activity by the sequential actions of E1, E2 and E3 enzymes to influence diverse aspects of eukaryotic cells. However, due to the diversity of proteins in cells, substrate selection is a highly critical part of the process. As a key player in UPS, E3 ubiquitin ligases recruit substrates for ubiquitination specifically. Among them, RING E3 ubiquitin ligases which are the most abundant E3 ubiquitin ligases contribute to diverse cellular processes. The multisubunit cullin-RING ligases (CRLs) are the largest family of RING E3 ubiquitin ligases with tremendous plasticity in substrate specificity and regulate a vast array of cellular functions. The F-box protein Skp2 is a component of CRL1 (the prototype of CRLs) which is expressed in many tissues and participates in multiple cellular functions such as cell proliferation, metabolism, and tumorigenesis by contributing to the ubiquitination and subsequent degradation of several specific tumor suppressors. Most importantly, Skp2 plays a pivotal role in a plethora of cancer-associated signaling pathways. It enhances cell growth, accelerates cell cycle progression, promotes migration and invasion, and inhibits cell apoptosis among others. Hence, targeting Skp2 may represent a novel and attractive strategy for the treatment of different human cancers overexpressing this oncogene. In this review article, we summarized the known roles of Skp2 both in health and disease states in relation to the UPS.

Targeting siRNA in colorectal cancer therapy: Nanotechnology comes into view

Colorectal cancer (CRC) is known as one of the most important causes of death and mortality worldwide. Although several efforts have been made for finding new therapies, no achievements have been made in this area. Multidrug resistance (MDR) mechanisms are one of the key factors that could lead to the failure of chemotherapy. Moreover, it has been shown that various chemotherapy drugs are associated with several side effects. Hence, it seems that finding new drugs or new therapeutic platforms is required. Among different therapeutic approaches, utilization of nanoparticles (NPs) for targeting a variety of molecules such as siRNAs are associated with good results for the treatment of CRC. Targeting siRNA-mediated NPs could turn off the effects of oncogenes and MDR-related genes. In the current study, we summarized various siRNAs targeted by NPs which could be used for the treatment of CRC. Moreover, we highlighted other routes such as liposome for targeting siRNAs in CRC therapy.

Two Transcripts of FBXO5 Promote Migration and Osteogenic Differentiation of Human Periodontal Ligament Mesenchymal Stem Cells

OBJECTIVES

Enhanced migration and osteogenic differentiation of mesenchymal stem cells (MSCs) are beneficial for MSC-mediated periodontal tissue regeneration, a promising method for periodontitis treatment. FBXO5, a member of the F-box protein family, is involved in the osteogenic differentiation of MSCs. Here, we investigated the effect of FBXO5 on human periodontal ligament stem cells (hPDLSCs).

MATERIALS AND METHODS

hPDLSCs were isolated from periodontal ligament tissue. Lentivirus FBXO5 shRNA was used to silence FBXO5 expression. Two transcripts of FBXO5 were overexpressed and transduced into hPDLSCs via retroviral infection. Migration and osteogenic differentiation of hPDLSCs were evaluated using the scratch migration assay, alkaline phosphatase (ALP) activity, ALP staining, alizarin red staining, western blotting, and real-time polymerase chain reaction.

RESULTS

The expression of FBXO5 was upregulated after osteogenic induction in hPDLSCs. FBXO5 knockdown attenuated migration, inhibited ALP activity and mineralization, and decreased RUNX2, OSX, and OCN expression, while the overexpression of two transcript isoforms significantly accelerated migration, enhanced ALP activity and mineralization, and increased RUNX2, OSX, and OCN expression in hPDLSCs.

CONCLUSIONS

Both isoforms of FBXO5 promoted the migration and osteogenic differentiation potential of hPDLSCs, which identified a potential target for improving periodontal tissue regeneration.

Functional significance and therapeutic implication of ring-type E3 ligases in colorectal cancer

Accumulative studies revealed that E3 ubiquitin ligases have important roles in colorectal carcinogenesis. The pathogenic mechanisms of colorectal cancer (CRC) initiation and progression are complex and heterogeneous, involving somatic mutations, abnormal gene fusion, deletion or amplification and epigenetic alteration, which may cause aberrant expression or altered function of E3 ligases in CRC. Defects of E3 ligases have been reported to be involved in the molecular etiology and pathogenesis of CRC. The aberrant expressed E3 ligases can function as either oncogenes or tumor suppressors depending on ubiquiting target substrates in CRC. Recently, considerable progress has been made in our understanding of the potential roles of E3 ligase-mediated ubiquitylation in colorectal carcinogenesis. There are mainly two subtypes of E3 ubiquitin ligases in humans, as defined by the presence of either a HECT domain or a RING finger domain on the basis of structural similitude. Most cancer-associated E3 ligases participate in regulating the cell cycle, apoptosis, gene transcription, cell signaling and DNA repair, the critical parts of CRC tumorigenesis. In this review, we have provided a comprehensive summary of abnormally expressed E3 ligases and their related pivotal mechanistic effects in CRC. In particular, we have highlighted the function of RING-type E3 ubiquitin enzymes in modulating cancer signaling pathways, immunity and tumor microenvironment in CRC development and progression; their mechanism(s) of action in CRC involving both ubiquitylation-dependent and ubiquitylation-independent effects; and the potential of RING E3 ligases as molecular biomarkers for predicting patient prognosis and as therapeutic targets in CRC. A better understanding of E3 ligase-mediated substrates' ubiquitylation involved in the development of CRC will provide new insights into the pathophysiology mechanisms of CRC, and unravel novel prognostic markers and therapeutic strategies for CRC.

APC/C and retinoblastoma interaction: cross-talk of retinoblastoma protein with the ubiquitin proteasome pathway

The ubiquitin (Ub) ligase anaphase promoting complex/cyclosome (APC/C) and the tumour suppressor retinoblastoma protein (pRB) play key roles in cell cycle regulation. APC/C is a critical regulator of mitosis and G₁-phase of the cell cycle whereas pRB keeps a check on proliferation by inhibiting transition to the S-phase. APC/C and pRB interact with each other via the co-activator of APC/C, FZR1, providing an alternative pathway of regulation of G₁ to S transition by pRB using a post-translational mechanism. Both pRB and FZR1 have complex roles and are implicated not only in regulation of cell proliferation but also in differentiation, quiescence, apoptosis, maintenance of chromosomal integrity and metabolism. Both are also targeted by transforming viruses. We discuss recent advances in our understanding of the involvement of APC/C and pRB in cell cycle based decisions and how these insights will be useful for development of anti-cancer and anti-viral drugs.

Knockdown of AMPKα2 Promotes Pulmonary Arterial Smooth Muscle Cells Proliferation via mTOR/Skp2/p27(Kip1) Signaling Pathway

It has been shown that activation of adenosine monophosphate-activated protein kinase (AMPK) suppresses proliferation of a variety of tumor cells as well as nonmalignant cells. In this study, we used post-transcriptional gene silencing with small interfering RNA (siRNA) to specifically examine the effect of AMPK on pulmonary arterial smooth muscle cells (PASMCs) proliferation and to further elucidate its underlying molecular mechanisms. Our results showed that knockdown of AMPKα2 promoted primary cultured PASMCs proliferation; this was accompanied with the elevation of phosphorylation of mammalian target of rapamycin (mTOR) and S-phase kinase-associated protein 2 (Skp2) protein level and reduction of p27(Kip1). Importantly, prior silencing of mTOR with siRNA abolished AMPKα2 knockdown-induced Skp2 upregulation, p27(Kip1) reduction as well as PASMCs proliferation. Furthermore, pre-depletion of Skp2 by siRNA also eliminated p27(Kip1) downregulation and PASMCs proliferation caused by AMPKα2 knockdown. Taken together, our study indicates that AMPKα2 isoform plays an important role in regulation of PASMCs proliferation by modulating mTOR/Skp2/p27(Kip1) axis, and suggests that activation of AMPKα2 might have potential value in the prevention and treatment of pulmonary arterial hypertension.

Ubiquitin proteasome system research in gastrointestinal cancer

The ubiquitin proteasome system (UPS) is important for the degradation of proteins in eukaryotic cells. It is involved in nearly every cellular process and plays an important role in maintaining body homeostasis. An increasing body of evidence has linked alterations in the UPS to gastrointestinal malignancies, including esophageal, gastric and colorectal cancers. Here, we summarize the current literature detailing the involvement of the UPS in gastrointestinal cancer, highlighting its role in tumor occurrence and development, providing information for therapeutic targets research and anti-gastrointestinal tumor drug design.

Involvement of F-BOX proteins in progression and development of human malignancies

The Ubiquitin Proteasome System (UPS) is a core regulator with various protein components (ubiquitin-activating E1 enzymes, ubiquitin-conjugating E2 enzymes, ubiquitin-protein E3 ligases, and the 26S proteasome) which work together in a coordinated fashion to ensure the appropriate and efficient proteolysis of target substrates. E3 ubiquitin ligases are essential components of the UPS machinery, working with E1 and E2 enzymes to bind substrates and assist the transport of ubiquitin molecules onto the target protein. As the UPS controls the degradation of several oncogenes and tumor suppressors, dysregulation of this pathway leads to several human malignancies. A major category of E3 Ub ligases, the SCF (Skp-Cullin-F-box) complex, is composed of four principal components: Skp1, Cul1/Cdc53, Roc1/Rbx1/Hrt1, and an F-box protein (FBP). FBPs are the substrate recognition components of SCF complexes and function as adaptors that bring substrates into physical proximity with the rest of the SCF. Besides acting as a component of SCF complexes, FBPs are involved in DNA replication, transcription, cell differentiation and cell death. This review will highlight the recent literature on three well characterized FBPs SKP2, Fbw7, and beta-TRCP. In particular, we will focus on the involvement of these deregulated FBPs in the progression and development of various human cancers. We will also highlight some novel substrates recently identified for these FBPs.

Roles of F-box proteins in human digestive system tumors (Review)

F-box proteins (FBPs), the substrate-recognition subunit of E3 ubiquitin (Ub) ligase, are the important components of Ub proteasome system (UPS). FBPs are involved in multiple cellular processes through ubiquitylation and subsequent degradation of their target proteins. Many studies have described the roles of FBPs in human cancers. Digestive system tumors account for a large proportion of all the tumors, and their mortality is very high. This review summarizes for the first time the roles of FBPs in digestive system tumorige-nesis and tumor progression, aiming at finding new routes for the rational design of targeted anticancer therapies in digestive system tumors.