Ubiquitin-specific protease 14 regulates ovarian cancer cisplatin-resistance by stabilizing BCL6 oncoprotein

https://doi.org/10.1016/j.bbrc.2020.01.150Get rights and content

Highlights

  • USP14 is overexpressed in cisplatin-resistant ovarian cancer cells.

  • USP14 promotes ovarian cancer cell proliferation.

  • USP14 controls the stability of BCL6.

  • BCL6 is required for cisplatin resistance in ovarian cancer cells A2780CP.

Abstract

Ubiquitin-specific protease 14 (USP14) is one of the three proteasome-associated deubiquitinating enzymes and implicated in the progression of various cancers. However, the role of USP14 in ovarian cancer remains unknown. By using an unbiased qRT-PCR screen, here we show that USP14 is considerably increased in cisplatin-resistant ovarian cancer cells. Overexpression of USP14 confers resistance to cisplatin-sensitive ovarian cancer cells. Genetic or pharmacological inhibition of USP14 is able to reverse cisplatin-resistance of ovarian cancer cells, which was accompanied by decreased protein expression of BCL6. Besides, BCL6 protein level was also increased in cisplatin-resistant ovarian cancer cells and silencing of BCL6 in these cells restored their sensitivity to cisplatin. At the molecular lever, we found that USP14 interacted with BCL6 and prevented it from proteasomal-dependent degradation. Thus, our results provide a rationale to target USP14-BCL6 axis in ovarian cancer that may be therapeutically beneficial.

Introduction

Ovarian cancer is one of the common malignant tumors of female genital organs. Its incidence is less than cervical cancer and endometrial cancer in gynecological malignant tumors, but with the highest mortality rate [1]. Most ovarian cancers are diagnosed at an advanced stage, and the 5-year survival rate is about 30% [2]. The treatment of ovarian cancer is mainly based on surgery, supplemented by chemotherapy, targeted therapy and other comprehensive treatments [3]. The treatment of advanced ovarian cancer is slightly different from other advanced tumors. When possible, it can be treated with surgery for cytoreductive treatment, and then assisted with platinum drugs for chemotherapy [4]. However, despite these advantages, the prognosis of advanced ovarian cancer is still unsatisfactory and about 70% of ovarian cancer patients died because of tumor recurrence and chemotherapy resistance within 5 years [5]. Therefore, it is crucial to understand the mechanism of ovarian cancer resistance to platinum drugs and to identify new targets for ovarian cancer treatment.

Ubiquitination is a post-translational modification that usually targets a substrate protein for proteasome-dependent degradation. Ubiquitination requires a three steps enzymatic process and implicated in numerous physiological and pathological processes, including signal transduction, cell cycle regulation, protein trafficking, DNA damage repair and cancer [6]. Importantly, ubiquitination is also a reversible process, and the deubiquitinating enzymes (DUBs) prevent protein degradation through the removal of ubiquitin from their substrates [7]. Recently, DUBs have emerged as potential targets for pharmacological intervention of various diseases, including neurological disorders, infectious diseases, and cancer [8]. However, the role of DUBs in cisplatin-resistant ovarian cancer cells remains to be elucidated.

The deubiquitinating enzyme USP14 belongs to the ubiquitin-specific protease (USP) family and specifically interacts with the 26 S proteasome [9]. USP14 controls multiple cellular functions by regulating the conversion of some key proteins, thereby affecting the activation of multiple signaling pathways [10]. USP14 also plays an important role in tumorigenesis, making it a critical drug target for cancer treatment [11]. It has been reported that USP14 serves as a positive regulator of the Wnt signaling pathway. USP14 can affect the phosphorylation level of Dishevelled (Dvl) by regulating its ubiquitination level, thereby interfering with the activation of downstream Wnt signaling pathway [12]. In addition, USP14 and β-catenin are highly correlated in the expression level of HCC, suggesting that high expression of USP14 may enhance Wnt/β-catenin signaling pathway and promote tumor cell proliferation [12]. Despite this progress, the role of USP14 in ovarian cancer remains completely unknown.

BCL6 is a transcription factor that is involved in chromosomal translocations in diffuse large B-cell lymphoma and nodular lymphocyte predominant Hodgkin lymphoma [13]. Recent studies found that BCL6 was also overexpressed in non-haematopoietic lineages and even in several cancer types [14]. BCL6 is targeted for ubiquitylation and proteasomal degradation by FBXO11 [15]. However, the deubiquitination enzyme of BCL6 has not been identified.

In this study, we found that USP14 is overexpressed in cisplatin-resistant ovarian cancer cells and required for cisplatin resistance. Genetic or pharmacological inhibition of USP14 recovered their sensitivity to cisplatin, leading to enhanced proteasomal-dependent degradation of BCL6.

Section snippets

Cell lines and reagents

Human ovarian cancer cell lines A2780, COC1and cisplatin-resistant subline A2780/CP, COC1/CP were purchased from SUER Biological Inc. (Shanghai, China). Cells were cultured in Dulbecco’s modified Eagle Medium (DMEM; Gibco BRL, Grand Island, NY, USA) with 10% FBS (Gibco, Gaithersburg, MD, USA), 100 U/ml penicillin and 100 μg/mL streptomycin (Beyotime, China), and maintained at 37 °C in a humidified chamber (5% CO2). Cisplatin was purchased from abcam (ab141398). Cycloheximide (239764) was

USP14 is overexpressed in cisplatin-resistant ovarian cancer cells

To investigate which deubiquitination enzymes are involved in cisplatin resistance, we examined the mRNA expression levels of several members of the USP family in cisplatin-sensitive ovarian cancer cells A2780 and cisplatin-resistant cells A2780CP by QRT-RCR. Interestingly, USP14 is the only member whose mRNA expression was dramatically increased in A2780CP cells compared with that in A2780 cells (Fig. 1A). Consistent with the mRNA levels, the USP14 protein levels were also significantly

Discussion

B cell lymphoma (BCL) family genes play an important role in the regulation of cells apoptosis. More than 25 genes have been found in this family, which could be divided into two subfamilies with either apoptosis promotion or inhibition ability [19]. The proto-oncogene BCL6 is originally found in malignant lymphoma, and its high expression is associated with the prognosis of some lymphoma patients [13]. BCL6 also belongs to BCL family with anti-apoptotic effects and is a sequence-specific

Declaration of competing interest

The authors declared that they have no conflicts of interest to this work.

Acknowledgements

This work was partially supported by grant from the Jingzhou Central Hospital of Jingzhou City

References (22)

  • T.E.T. Mevissen et al.

    Mechanisms of deubiquitinase specificity and regulation

    Annu. Rev. Biochem.

    (2017)
  • Cited by (16)

    • Implication of BAG5 downregulation in metabolic reprogramming of cisplatin-resistant ovarian cancer cells via mTORC2 signaling pathway

      2021, Biochimica et Biophysica Acta - Molecular Cell Research
      Citation Excerpt :

      These data indicated that −1031 to −564 fragment of BAG5 promoter might contain the regulatory elements responsible for different transactivation in cisplatin-sensitive and cisplatin-resistant ovarian cancer cells. Bcl6 attracted our attention while searching on BAG5 gene because of the following reasons: firstly, a potential Bcl6 responsive elements located on −739 to −724 of BAG5 gene just falls into the regulatory region responsible for different transactivation in cisplatin-resistant and cisplatin-sensitive ovarian cancer cells; secondly, it has been reported that Bcl6 is upregulated in cisplatin-resistant ovarian cancer [32], and Bcl6 functions as a oncogene and its high expression is a negative prognostic factor in patients with ovarian cancer [33–35]; thirdly, Bcl6 functions as a transcriptional repressor for a variety of genes [36–39]. Western blot confirmed an increase of Bcl6 expression in SKOV3/DDP and A2780/DDP cells (Fig. 6E).

    • Ubiquitin-specific protease 14 promotes radio-resistance and suppresses autophagy in oral squamous cell carcinoma

      2021, Experimental Cell Research
      Citation Excerpt :

      USP14 can modulate the progression of multiple different kinds of tumors, including OSCC, through mediating cancer cell proliferation, apoptosis and cell cycle arrest [8–10]. Additionally, the expression change of USP14 is associated with drug resistance in myeloma and ovarian cancer [11,12]. Tumor cell sensitivity to radiotherapy has been reported as a key influencing factor that regulates the prognosis of patients with OSCC [19].

    View all citing articles on Scopus
    View full text