Frequent Nek1 overexpression in human gliomas

https://doi.org/10.1016/j.bbrc.2016.05.156Get rights and content

Highlights

  • Nek1 is upregulated in multiple human glioma tissues and cell lines.

  • Nek1 overexpression correlates with glioma grades and patients’ KPS score.

  • Nek1 overexpression correlates with patients’ poor overall survival.

  • siRNA knockdown of Nek1 inhibits glioma cell growth.

  • siRNA knockdown of Nek1 sensitizes human glioma cells to temozolomide.

Abstract

Never in mitosis A (NIMA)-related kinase 1 (Nek1) regulates cell cycle progression to mitosis. Its expression and potential functions in human gliomas have not been studied. Here, our immunohistochemistry (IHC) assay and Western blot assay results showed that Nek1 expression was significantly upregulated in fresh and paraffin-embedded human glioma tissues. Its level in normal brain tissues was low. Nek1 overexpression in human gliomas was correlated with the proliferation marker (Ki-67), tumor grade, Karnofsky performance scale (KPS) and more importantly, patients’ poor survival. Further studies showed that Nek1 expression level was also increased in multiple human glioma cell lines (U251-MG, U87-MG, U118, H4 and U373). Significantly, siRNA-mediated knockdown of Nek1 inhibited glioma cell (U87-MG/U251-MG) growth. Nek1 siRNA also sensitized U87-MG/U251-MG cells to temozolomide (TMZ), causing a profound apoptosis induction and growth inhibition. The current study indicates Nek1 might be a novel and valuable oncotarget of glioma, it is important for glioma cell growth and TMZ-resistance.

Introduction

Glioma patients are often with low five-year survival [1]. The prognosis of glioblastoma multiforme (GBM), or grade IV glioma, is extremely poor [2], [3], [4]. Postoperative radiation and/or temozolomide (TMZ) are the current standard treatments for glioma [2], [5], [6]. Yet, the overall survival has not been improved [2], [5], [6]. One hurdle is the molecular heterogeneity of glioma [3]. Therefore, it is extremely important to identify novel and valuable oncotargets of human glioma [3].

Never in mitosis A (NIMA) was originally identified in Aspergillus nidulans as a serine/threonine kinase [7], [8]. It is important for cell cycle progression [7], [8]. Studies have shown that dominant-negative form of NIMA could inhibit the progression of cell cycle into mitosis [9]. Human NIMA-related kinases (Neks) have high homology to NIMA in their N-terminal catalytic domain, but diverge substantially from NIMA at their non-catalytic C-terminals [10]. Thus far, at least eleven human Neks have been identified [9], [10]. It is now known that Neks exert similar functions as NIMA, and regulate cell cycle progression and mitosis [9], [10].

Nek1 is an important member of Nek family kinases [11], [12]. Studies demonstrate that Nek1 expression and activity are increased during mitosis [11], [12]. On the other hand, overexpression of a dominant negative form of Nek1 or Nek1 siRNA caused spindle defects, abnormal chromosome segregation, mitotic arrest and cell apoptosis [9], [11], [12], [13]. Considering that both cell cycle progression and mitosis are key players of tumor cell progression, we here tested expression and potential functions of Nek1 in human gliomas.

Section snippets

Primary human glioma specimens and immunohistochemistry (IHC) assay

Human glioma specimens (n = 70, from 2000 to 2013) were collected using protocols approved by the Ethics Committee of the Shanghai Jiao Tong University. All tumors were from patients with newly diagnosed glioma (no prior radiation or chemotherapy treatment). Formalin-fixed, paraffin-embedded sections were prepared and reviewed by two double-blinded neuropathologists. Normal brain specimens were acquired from ten patients undergoing surgery for epilepsy at the Ruijin Hospital, Shanghai Jiao Tong

Nek1 overexpression in human glioma tissues and cells

First, Western blot assay was applied to test protein expression of Nek1 in a panel of fresh human glioma operative specimens. As compared to the normal brain tissues, Nek1 protein expression in glioma tissues was significantly upregulated (Fig. 1A and B). Further, Nek1 overexpression was more significant in high-grade glioma tissues (Fig. 1A and B). Overexpression of Nek1 was also detected in several human glioma cell lines, including U251-MG, U87-MG, U118, H4 and U373 (Fig. 1C and D). Note

Discussion

NIMA family kinases are important for cell cycle regulation [7], [8], [9], [16]. The NIMA homologous kinase Nek shows high homology sequence with NIMA in the N-terminal catalytic domain [10]. At least eleven Neks have been characterized thus far [10]. Recent studies have implied that Neks are also important for tumor progression and apoptosis-resistance [17]. For example, Nek8 expression is upregulated in primary human breast tumors [17]. Overexpression of inactive Nek8 decreased the growth

Conflicts of interest

The authors declare no conflict of interest.

References (17)

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