FBXW7 expression affects the response to chemoradiotherapy and overall survival among patients with oral squamous cell carcinoma: A single-center retrospective study

FBXW7 promotes autophagy and inhibits proliferation of oral squamous cell carcinoma

BACKGROUND

F-box and WD repeat domain containing 7 (FBXW7) is a critical tumor suppressor. The expression of FBXW7 is decreased in oral squamous cell carcinoma (OSCC) tissues and shows diagnosis value. We aimed to investigate the influence of FBXW7 overexpression on OSCC cell proliferation and autophagy.

METHODS

In Balb/c nude mice, CAL27 xenograft tumor model was established. Western blot was employed to evaluate protein level. Messenger RNA level was analyzed by quantitative reverse transcription-polymerase chain reaction. Colony formation assay and MTT assay were employed to evaluate cell proliferation.

RESULTS

FBXW7 expression was decreased in OSCC cell lines. FBXW7 inhibited cell proliferation of SCC9 and CAL27. FBXW7 increased Autophagy related 7 (Atg7), Beclin1 (BECN1), B-cell lymphoma 2 (BCL2) -associated X (BAX), BCL2 antagonist killer (BAK), and microtubule-associated protein 1 light chain 3 (LC3) levels and decreased MCL1 and BCL2 levels in CAL27 cells. FBXW7 decreased tumor volume and weight in CAL27 xenograft tumor model. FBXW7 increased BECN1, Atg7, and LC3 levels in CAL27 xenograft tumor model.

CONCLUSION

In conclusion, decreased expression of FBXW7 is confirmed in diverse OSCC cell lines. The enhanced FBXW7 expression inhibits cancer cell proliferation and promotes autophagy in both OSCC cells and xenograft tumor model.

Molecular mechanism of FBXW7-mediated ubiquitination modification in nasopharyngeal carcinoma cell proliferation in vitro and in vivo

OBJECTIVES

Nasopharyngeal carcinoma (NPC) is a type of keratinizing squamous cell malignancy. Ubiquitination, a common protein posttranslational modification, participates in cancer development. This study sought to investigate the mechanism of F-box and WD repeat domain containing 7 (FBXW7) in NPC cell proliferation in vivo and in vitro.

METHODS

FBXW7, Homeobox A10 (HOXA10), and bone morphogenetic protein-2 (BMP2) expression levels in NPC tissues and cells were detected by RT-qPCR and Western blotting. Cell proliferation was assessed by cell counting kit-8 and colony formation assays. The binding of FBXW7 to HOXA10 and HOXA10 ubiquitination level were detected via co-immunoprecipitation and ubiquitination assay. Cells were treated with MG132 (the proteasome inhibitor), followed by the determination of HOXA10 ubiquitination and protein levels. The binding of HOXA10 to BMP2 was testified via dual-luciferase and chromatin immunoprecipitation assays. Collaborative experiments were performed to confirm the role of HOXA10 or BMP2 in FBXW7-mediated NPC cell proliferation. Xenograft tumor assay was performed to confirm the role of FBXW7/HOXA10/BMP2 in vivo.

RESULTS

FBXW7 was under-expressed, while HOXA10 and BMP2 were up-expressed in NPC tissues and cells. FBXW7 overexpression restricted NPC cell proliferation. Mechanically, FBXW7 bound to HOXA10 to promote ubiquitination-based degradation of HOXA10 and further reduced the binding of HOXA10 to the BMP2 promoter and inhibited BMP2 transcription. Overexpression of HOXA10 or BMP2 attenuated the role of FBXW7 overexpression in inhibiting NPC cell proliferation. FBXW7 overexpression reduced Ki67 positive rate and repressed tumor growth.

CONCLUSION

FBXW7 overexpression promoted HOXA10 ubiquitination-based degradation and further inhibited BMP2 transcription, consequently restricting NPC cell proliferation in vitro and in vivo.

Clinicopathologic Characteristics of FBXW7-Mutated Colorectal Adenocarcinoma and Association with Aberrant Beta-catenin Localization

Oncogenic mutations in the adenomatous polyposis coli (APC)/Wnt signaling pathway are well documented. The FBXW7 gene (F-Box And WD Repeat Domain Containing 7) encodes a member of the ubiquitin-proteasome complex that is more recently described to antagonize the oncogenic Wnt pathway by promoting the degradation of β-catenin encoded by CTNNB1 gene. The pathologic significance of FBXW7 mutation in colorectal carcinoma (CRC) remains underreported. In this study, we report the clinicopathologic and β-catenin immunohistochemical features of a single-institution cohort (83 cases) of FBXW7-mutated CRC compared to CTNNB1-mutated CRC. FBXW7-mutated CRC was more common in older patients (p=0.031) and in the left/distal colon (p=0.022). Immunohistochemical analysis revealed that aberrant nuclear/cytoplasmic β-catenin localization was identified in a significantly high proportion of FBXW7-mutated CRCs. When compared to CTNNB1-mutated CRC, FBXW7-mutated CRC showed a significantly higher proportion of MSI-stable tumors with intact expression of DNA mismatch repair proteins, and had significantly more frequent co-occurrence of missense TP53 and KRAS mutations. The most frequently mutated FBXW7 residues/hotspots were located within the WD repeat domains (aa 378-659), which were also associated with aberrant nuclear/cytoplasmic localization of β-catenin protein. Our results indicate the unique pathologic characteristics of FBXW7 mutated CRC with frequent co-occurrence of missense mutant TP53, and KRAS. The mutated FBXW7 residues/hotspots and its association with aberrant nuclear/cytoplasmic β-catenin localization further support the oncogenic role of FBXW7 in colon carcinogenesis.

USP28: Oncogene or Tumor Suppressor? A Unifying Paradigm for Squamous Cell Carcinoma

Squamous cell carcinomas are therapeutically challenging tumor entities. Low response rates to radiotherapy and chemotherapy are commonly observed in squamous patients and, accordingly, the mortality rate is relatively high compared to other tumor entities. Recently, targeting USP28 has been emerged as a potential alternative to improve the therapeutic response and clinical outcomes of squamous patients. USP28 is a catalytically active deubiquitinase that governs a plethora of biological processes, including cellular proliferation, DNA damage repair, apoptosis and oncogenesis. In squamous cell carcinoma, USP28 is strongly expressed and stabilizes the essential squamous transcription factor ΔNp63, together with important oncogenic factors, such as NOTCH1, c-MYC and c-JUN. It is presumed that USP28 is an oncoprotein; however, recent data suggest that the deubiquitinase also has an antineoplastic effect regulating important tumor suppressor proteins, such as p53 and CHK2. In this review, we discuss: (1) The emerging role of USP28 in cancer. (2) The complexity and mutational landscape of squamous tumors. (3) The genetic alterations and cellular pathways that determine the function of USP28 in squamous cancer. (4) The development and current state of novel USP28 inhibitors.

Suppression of KIF22 Inhibits Cell Proliferation and Xenograft Tumor Growth in Tongue Squamous Cell Carcinoma

Background

Oral carcinoma is the sixth most common cancer and is a serious public health problem, and tongue squamous cell carcinoma (TSCC) is the most common type of oral carcinoma. Kinesin family member 22 (KIF22), also called as kinesin-like DNA binding protein (KID), is a microtubule-based motor protein and binds to both microtubules and chromosomes, transporting organelles, protein, and mRNA. This research aimed at investigating the prognostic significance of KIF22 in TSCC. Patients and Methods. This retrospective research collected 82 paired tissues with TSCC. KIF22 protein expression level was detected by immunohistochemical staining. Suppression of KIF22 with shRNA in CAL-27 and SCC-15 cells was to observe cell proliferation in vitro and xenograft tumor growth in vivo.

Results

In TSCC tissues, the protein expression level of KIF22 was increased and correlated with tumor stage, clinical stage, and lymphatic metastasis (P=0.013, P=0.013, P=0.013,

Conclusion

KIF22 might play an important role in the progression of TSCC and could serve as a therapeutic target for TSCC.

Emerging roles of F-box proteins in cancer drug resistance

Chemotherapy continues to be a major treatment strategy for various human malignancies. However, the frequent emergence of chemoresistance compromises chemotherapy efficacy leading to poor prognosis. Thus, overcoming drug resistance is pivotal to achieve enhanced therapy efficacy in various cancers. Although increased evidence has revealed that reduced drug uptake, increased drug efflux, drug target protein alterations, drug sequestration in organelles, enhanced drug metabolism, impaired DNA repair systems, and anti-apoptotic mechanisms, are critically involved in drug resistance, the detailed resistance mechanisms have not been fully elucidated in distinct cancers. Recently, F-box protein (FBPs), key subunits in Skp1-Cullin1-F-box protein (SCF) E3 ligase complexes, have been found to play critical roles in carcinogenesis, tumor progression, and drug resistance through degradation of their downstream substrates. Therefore, in this review, we describe the functions of FBPs that are involved in drug resistance and discuss how FBPs contribute to the development of cancer drug resistance. Furthermore, we propose that targeting FBPs might be a promising strategy to overcome drug resistance and achieve better treatment outcome in cancer patients. Lastly, we state the limitations and challenges of using FBPs to overcome chemotherapeutic drug resistance in various cancers.

F-Box/WD Repeat Domain-Containing 7 Induces Chemotherapy Resistance in Colorectal Cancer Stem Cells

Although the cancer stem cell (CSC) concept has provided a reasonable explanation for cancer recurrence following chemotherapy, the relationship between CSCs and chemotherapy resistance has not been thoroughly investigated, especially in solid tumors. We aimed to identify the mechanism underlying colorectal cancer (CRC) chemoresistance focusing on the cell cycle mediator F-Box/WD repeat domain-containing 7 (FBXW7). From 55 consecutive CRC cases who underwent neoadjuvant chemotherapy (NAC) or neoadjuvant chemoradiotherapy (NACRT) at Kyoto University Hospital, pre-treatment endoscopic biopsy specimens were collected and divided into two groups upon immunohistochemical (IHC) analysis: 21 cases of FBXW7 high expression (FBXW7-high group) and 34 cases of low expression (FBXW7-low group). High FBXW7 expression in pre-treatment biopsy specimen was significantly associated with poor pathological therapeutic effect (p = 0.019). The proportion of FBXW7-positive cells in surgically resected CRC specimens from patients who underwent NAC or NACRT was significantly higher than that in the pre-treatment biopsy specimens (p < 0.001). The expression of FBXW7 was inversely correlated with that of Ki67 in both pre-treatment biopsy specimens and surgically resected specimens. FBXW7 expression in the EpCAM^high/CD44^high subpopulation isolated by flow cytometry from CRC samples was significantly higher than that in the EpCAM^high/CD44^low subpopulation. Cell-cycle analysis in CRC cell lines revealed that, upon FBXW7 silencing, the proportion of G0/G1 cells was significantly lower than that in control cells. Moreover, knockdown of FBXW7 in CRC cell lines increased the sensitivity to anti-cancer drugs in vitro and in vivo. A subset of CRC stem cells possesses chemoresistance through FBXW7 expression. Cell cycle arrest induced by FBXW7 expression should be considered as a potential therapeutic target to overcome chemoresistance in CRC stem cell subsets.

F-box/WD-40 repeat-containing protein 7: A potential target in the progression and treatment of gastrointestinal malignancy

Cancer is a principal cause of human morbidity and mortality, with gastrointestinal malignancies, in particular, resulting in a marked number of tumor-associated mortalities. The progression of gastrointestinal malignancy is regulated by a variety of aberrantly expressed proteins, a number of which facilitate tumor progression, whereas, others function as tumor suppressors. The detection of such proteins not only contributes to the early diagnosis of cancer, they may additionally serve as potential therapeutic targets. In normal tissues, numerous proteins encoded by proto-oncoproteins are degraded by ubiquitylation enzymes, consisting of F-box/WD-40 repeat-containing protein 7 (Fbw7) and other proteins, thus avoiding tumorigenesis and maintaining homeostasis. In tumor tissues, the downregulation of Fbw7, caused by various factors, leads to disorders in ubiquitinase synthesis, which may induce tumor progression and chemoresistance, particularly in gastrointestinal malignancy. Therefore, an in-depth study of the regulatory mechanisms involved in disorders of Fbw7 expression and the role of Fbw7 in chemoresistance of gastrointestinal tumors may suggest improvements for early diagnostic screening and targeted therapy.

FBXW7 in Cancer: What Has Been Unraveled Thus Far?

: The FBXW7 (F-box with 7 tandem WD40) protein encoded by the gene FBXW7 is one of the crucial components of ubiquitin ligase called Skp1-Cullin1-F-box (SCF) complex that aids in the degradation of many oncoproteins via the ubiquitin-proteasome system (UPS) thus regulating cellular growth. FBXW7 is considered as a potent tumor suppressor as most of its target substrates can function as potential growth promoters, including c-Myc, Notch, cyclin E, c-JUN, and KLF5. Its regulators include p53, C/EBP-δ, Numb, microRNAs, Pin 1, Hes-5, BMI1, Ebp2. Mounting evidence has indicated the involvement of aberrant expression of FBXW7 for tumorigenesis. Moreover, numerous studies have also shown its role in cancer cell chemosensitization, thereby demonstrating the importance of FBXW7 in the development of curative cancer therapy. This comprehensive review emphasizes on the targets, functions, regulators and expression of FBXW7 in different cancers and its involvement in sensitizing cancer cells to chemotherapeutic drugs.