The oncoprotein HBXIP up-regulates Skp2 via activating transcription factor E2F1 to promote proliferation of breast cancer cells
Introduction
The hepatitis B virus X-interacting protein (HBXIP), encoding a 18 kDa protein, was originally identified by its interaction with the C-terminus of the hepatitis B virus X protein (HBx) and located at human chromosome 1 p13.3 [1]. HBXIP inhibited the apoptosis induced by HBx in hepotoma cells [2]. HBXIP could form complex with survivin, an anti-apoptotic protein that was overexpressed in most human cancers [1], [3], resulting in the suppression of apoptosis through the mitochondrial/cytochrome pathway. HBXIP was also required for bipolar spindle formation and was a regulator of centrosome dynamics and cytokinesis in cells [4]. Our previous studies reported that HBXIP could promote cell proliferation and migration through S100A4 and IL-8 [5], [6]. However, the mechanism by which HBXIP enhances the proliferation of breast cancer cells remains unclear.
S-phase kinase-associated protein 2 (Skp2) belongs to the family of the F-box proteins. It was originally discovered by Beach and colleagues in 1995, because of its ability to interact with the cell cycle protein cyclin A [7]. Skp2 contains the N-terminal domain, F-box domain, and C-terminal leucine-rich repeats (LRRs) [8]. The Skp2 protein levels changes during the cell cycle, which is low in early G1 phase, while it is high during G1/S transition [9]. This alteration in the Skp2 protein level during cell cycle progression is partly due to a change in its gene expression and protein stability [10]. Co-transfection of cyclin E and Skp2 synergistically promoted cell cycle progression in cultured primary hepatocytes in the absence of mitogen or in the presence of growth inhibitors. Furthermore, transfection of hepatocytes in vivo with cyclin E and Skp2 promoted abundant hepatocyte replication and hyperplasia of the liver [11]. Subsequent experiments revealed that Skp2 was involved in cell cycle progression. Overexpression of Skp2 was frequently observed in numerous human cancers, such as colorectal, gastric, breast, prostate, lung, sarcoma, ovarian and other cancers [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]. These observations suggest that Skp2 may contribute to the development of human cancers. Accumulated evidence suggests that Skp2 displays a proto-oncogenic role in vitro and in vivo.
In the present study, we try to gain insight into the effect of HBXIP on regulation of Skp2 in promotion of proliferation of breast cancer cells. Our data indicate that HBXIP is able to up-regulate Skp2 through E2F1 in breast cancer cells, resulting in the promotion of cell proliferation. Our findings provide insights into the mechanisms by which HBXIP enhances the proliferation of breast cancer cells.
Section snippets
Immunohistochemistry (IHC)
Breast cancer tissue array (No. 08C14), comprising 49 breast tumors, was purchased from Xi’an Aomei Biotechnology (Xi’an, China). Immunohistochemistry assay was performed as described previously [6]. The slides were incubated with rabbit anti-HBXIP (Proteintech Group, Chicago, USA) (or rabbit anti-Skp2, Boster Group, Wuhan, China) antibody at 4 °C for overnight. After incubation at room temperature for 30 min with biotinylated secondary antibody, the slides were incubated with
The expression levels of HBXIP are positively associated with those of Skp2 in clinical breast cancer tissues
Our previous report showed that 75% clinical breast cancer tissues were positive for HBXIP by IHC staining [6]. It has been reported that Skp2 is overexpressed in breast cancer tissues and cell lines [14]. Thus, we supposed that Skp2 might be correlated with HBXIP in breast cancer. Then, we try to investigate the expression correlation between HBXIP and Skp2 by IHC using tissue arrays which are from the same tissue paraffin block. Our data showed that the positive rate of HBXIP was 77.55%
Discussions
Our studies show that HBXIP is a novel oncoprotein. HBXIP was highly expressed in breast cancer tissues and metastatic lymph node tissues and significantly associated with the growth and metastasis of breast cancer cells [6], [32]. However, the underlying mechanism is poorly understood. Skp2 has an established role in tumors. Many studies have shown that the over-expression of Skp2 is observed in a variety of human cancers, including colorectal cancer, gastric cancer, breast cancer, prostate
Acknowledgements
This work was supported by grants from the National Basic Research Program of China (973 Program, Nos. 2011CB512113, and 2009CB521702) and National Natural Science Foundation of China (Nos. 81071623, 81071624 and 81272217).
References (40)
- et al.
The oncoprotein HBXIP uses two pathways to up-regulate S100A4 in promotion of growth and migration of breast cancer cells
J. Biol. Chem.
(2012) - et al.
MiR-520b regulates migration of breast cancer cells by targeting hepatitis B X-interacting protein and interleukin-8
J. Biol. Chem.
(2011) - et al.
p19Skp1 and p45Skp2 are essential elements of the cyclin A-CDK2 S phase kinase
Cell
(1995) - et al.
Crashing waves of destruction: the cell cycle and APC(Cdh1) regulation of SCF(Skp2)
Cancer cell
(2004) - et al.
Skp2 overexpression increases the expression of MMP-2 and MMP-9 and invasion of lung cancer cells
Cancer Lett.
(2010) - et al.
SKP2 oncogene is a direct MYC target gene and MYC down-regulates p27(KIP1) through SKP2 in human leukemia cells
J. Biol. Chem.
(2011) - et al.
Expression of Skp2, a p27(Kip1) ubiquitin ligase, in malignant lymphoma: correlation with p27(Kip1) and proliferation index
Blood
(2002) - et al.
The combination of high cyclin E and Skp2 expression in breast cancer is associated with a poor prognosis and the basal phenotype
Hum. Pathol.
(2008) - et al.
E2F1-regulated microRNAs impair TGFbeta-dependent cell-cycle arrest and apoptosis in gastric cancer
Cancer cell
(2008) - et al.
MiRNA-205 suppresses melanoma cell proliferation and induces senescence via regulation of E2F1 protein
J. Biol. Chem.
(2011)
Cloning and characterization of a novel hepatitis B virus X binding protein that inhibits viral replication
J. Virol.
Human ATP-dependent RNA/DNA helicase hSuv3p interacts with the cofactor of survivin HBXIP
FEBS. J.
HBXIP functions as a cofactor of survivin in apoptosis suppression
EMBO. J.
HBXIP, cellular target of hepatitis B virus oncoprotein, is a regulator of centrosome dynamics and cytokinesis
Cancer Res.
Deregulated proteolysis by the F-box proteins SKP2 and beta-TrCP: tipping the scales of cancer
Nat. Rev. Cancer
The amelioration of renal damage in Skp2-deficient mice canceled by p27 Kip1 deficiency in Skp2-/-p27-/-mice
PLoS. One.
Induction of hepatocyte proliferation and liver hyperplasia by the targeted expression of cyclin E and skp2
Oncogene
Skp2 overexpression is a prognostic factor in patients with ovarian adenocarcinoma
Clin. Cancer Res.
Clinical and biological significance of S-phase kinase-associated protein 2 (Skp2) gene expression in gastric carcinoma: modulation of malignant phenotype by Skp2 overexpression, possibly via p27 proteolysis
Cancer Res.
Significance of skp2 expression in primary breast cancer
Clin. Cancer Res.
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These authors contributed equally to the work.