F-box and leucine-rich repeat protein 5 promotes colon cancer progression by modulating PTEN/PI3K/AKT signaling pathway

doi:10.1016/j.biopha.2018.08.119

Biomedicine & Pharmacotherapy

Volume 107, November 2018, Pages 1712-1719

https://doi.org/10.1016/j.biopha.2018.08.119 Get rights and content

Abstract

The hyper-activation of PI3K/AKT signaling is common in many kinds of malignant tumors and promotes cell growth. Moreover, FBXL5 is reported to play an important role in the progression of gastric cancer and cervical cancer. In this view, this study aims to explore the function of FBXL5 in the progression of colon cancer and determine if PI3K/AKT signaling pathway involves in this process. Western blotting, RT-PCR, and immunohistochemistry were used to detect the expression pattern of FBXL5 in colon cancer tissues and cell lines. Immunofluorescence, Duolink, and immunoprecipitation (IP) assays were performed to evaluate the interaction between FBXL5 and PI3K/AKT signaling. Results showed that FBXL5 was elevated in colon cancer tissues and cells, which had physical interaction with PTEN protein and negatively regulated its expression, whereas positively modulated PI3K, AKT and mTOR expression and their phosphorylation. Besides, FBXL5 promoted cell proliferation and tumorigenesis and inhibited apoptosis by modulating PTEN/PI3K/AKT signaling. In conclusion, this study demonstrated that FBXL5 functioned as an oncogene in the progression of colon cancer through regulating PTEN/PI3K/AKT signaling.

Introduction

Colorectal carcinoma (CRC) ranks the third most common malignant tumor in men and the second most common type of malignant tumor in women [1]. In 2012, approximately 694,000 CRC-related deaths were recorded [1]. In patients with stage I disease, 5-year relative survival is greater than 90%. However, survival is only slightly greater than 10% in stage IV CRC patients [2,3]. Despite efforts have been made to improve clinical treatment, the prognosis of colon cancer patients has shown no marked progress in recent years. Therefore, it is essential to explore the cancer biology underlying colon cancer.

The ubiquitin protein ligase complex SKP1-cullin-F-box is made up of Skp1, Cullin 1, and an F-box protein that interacts with many substrates for proteasome-dependent destruction [4]. Accumulated evidence suggests that this complex plays crucial roles in tumorigenesis via modulating cell proliferation, apoptosis, metastasis, and angiogenesis [5]. For example, recent studies have identified that FBXW7 is a haplo-insufficient tumor suppressor, which targets several proto-oncoproteins, including cyclin E, c-Myc, c-jun, and Mcl1, for degradation [[6], [7], [8]]. F-box and leucine-rich repeat protein 5 (FBXL5) is a member of the F-box protein family, which is characterized by an F-box motif consisting of 40 amino acids [[9], [10], [11]]. Until now, FBXL5 is reported to function as a tumor suppressor in gastric cancer [[12], [13], [14]] and cervical cancer [15]. However, the effects of FBXL5 in colon cancer and the underlying molecular mechanism have remained unclear.

Phosphatase and tensin homolog, deleted on chromosome 10 (PTEN), a major tumor suppressor, has been identified to play a vital role in colon carcinogenesis [16]. PTEN induces lipid phosphatase activity and regulates cell survival and apoptosis through repressing the oncogenic PI3K/AKT signaling [17,18]. Besides, PTEN, as a phosphatase for phosphoinositol lipids, also plays an important role in the regulation of tumor metastasis [19], including colon cancer [20,21]. In our preliminary study, we found that overexpression of FBXL5 induced excessive activation of the PI3K/AKT signaling pathway in colon cancer (Fig. 3A). However, the molecular mechanism of FBXL5 and PI3K/AKT in colon cancer progression remains unclear.

In view of the association of FBXL5 expression with PI3K/AKT signaling activation, the present study investigated the effects and underlying mechanism of FBXL5 and PI3K/AKT in colon cancer occurrence and development. Results demonstrated that FBXL5 expression was elevated in colon cancer, which improved cell growth and tumorigenesis and repressed cell apoptosis by modulating the PI3K/AKT signaling pathway in which the expression PTEN was decreased, whereas that of AKT, PI3K, and mammalian rapamycin (mTOR) was increased. These findings point to a new therapeutic strategy for colon cancer.

Section snippets

Patients and sample preparation

The study was approved by the Human Research Committee of Southwest Medical University and was performed in accordance with the Helsinki Declaration. The colon cancer samples and paired adjacent non-tumor tissues were obtained from patients with colon cancer. And all of the patients receipted a radical colectomy only without any form of chemotherapy or radiation.

Immunohistochemistry

Paraffin sections of colon tissues were sliced into sections that were 4 μm thick by a slicing machine. Then, staining protocol was

Increased expression of FBXL5 in colon cancer tissues and cell lines

To explore the effects of FBXL5 on the development of colon cancer, we firstly determined the expression pattern of FBXL5 in colon cancer tissues and cell lines. Results of the immunohistochemistry analysis of FBXL5 expression in 29 paired colon cancer tissues and adjacent tissues showed that the score of FBXL5 protein expression in colon cancer tissues was significantly higher than that in the adjacent tissues (Fig. 1A). Western blotting and RT-PCR analysis demonstrated that both the protein

Discussion

FBXL5^−/− mice show an embryonic lethality phenotype, with growth defects readily apparent prior to day E9, despite normal placentation, cardiovascular, and gastrulation development [25]. Previous biochemical studies demonstrated that FBXL5 played a critical role in the maintenance of cellular iron homeostasis by targeting IRP1 and IRP2 for ubiquitination [26]. Research also showed that cells from FBXL5 knockout mice showed a tendency toward apoptosis due to unrestrained IRP activity, which is

Competing interests

The authors declare that they have no competing interests.

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F-box and leucine-rich repeat protein 5 promotes colon cancer progression by modulating PTEN/PI3K/AKT signaling pathway

Abstract

Introduction

Section snippets

Patients and sample preparation

Immunohistochemistry

Increased expression of FBXL5 in colon cancer tissues and cell lines

Discussion

Competing interests

Lancet

J. Biol. Chem.

J. Inorg. Biochem.

J. Biol. Chem.

Am. J. Pathol.

J. Biol. Chem.

Cell Metab.

J. Biol. Chem.

Eur. J. Surg. Oncol.

Global cancer statistics

CA Cancer J. Clin.

Personalizing colon cancer adjuvant therapy: selecting optimal treatments for individual patients

J. Clin. Oncol.

Mechanisms and function of substrate recruitment by F-box proteins

Nat. Rev. Mol. Cell Biol.

SCF ubiquitin ligase-targeted therapies

Nat. Rev. Drug Discov.

Phosphorylation-dependent ubiquitination of cyclin E by the SCFFbw7 ubiquitin ligase

Science

Phosphorylation-dependent degradation of c-Myc is mediated by the F-box protein Fbw7

EMBO J.

SCF(FBW7) regulates cellular apoptosis by targeting MCL1 for ubiquitylation and destruction

Nature

FBXL5 targets cortactin for ubiquitination-mediated destruction to regulate gastric cancer cell migration

Tumour Biol.

FBXL5 inhibits metastasis of gastric cancer through suppressing Snail1

Cell. Physiol. Biochem.

FBXL5 attenuates RhoGDI2-induced cisplatin resistance in gastric cancer cells

Eur. Rev. Med. Pharmacol. Sci.