- Open Access
PAK4 confers the malignance of cervical cancers and contributes to the cisplatin-resistance in cervical cancer cells via PI3K/AKT pathway
© Shu et al. 2015
Received: 21 July 2015
Accepted: 28 August 2015
Published: 28 September 2015
Multiple protein or microRNA markers have been recognized to contribute to the progression and recurrence of cervical cancers. Particular those, which are associated with the chemo- or radio-resistance of cervical cancers, have been proposed to be promising and to facilitate the definition for cervical cancer treatment options.
This study was designed to explore the potential prognosis value of p21-activated kinase (PAK)-4 in cervical cancer, via the Kaplan–Meier analysis, log-rank test and Cox regression analysis, and then to investigate the regulatory role of PAK4 in the cisplatin resistance in cervical cancer cells, via the strategies of both PAK4 overexpression and PAK4 knockout.
It was demonstrated that PAK4 was upregulated in cervical cancer tissues, in an association with the cancer’s malignance variables such as FIGO stage, lymph node or distant metastasis and the poor histological grade. The high PAK4 expression was also independently associated with poor prognosis to cervical cancer patients. Moreover, PAK4 confers cisplatin resistance in cervical cancer Hela or Caski cells. In addition, the PI3K/Akt pathway has been implicated in the PAK4-confered cisplatin resistance. And the PI3K/Akt inhibitor, LY294002, markedly deteriorated the cisplatin-mediated viability reduction of Hela or Caski cells, indicating the involvement of PI3K/Akt pathway in the cisplatin resistance in cervical cancer cells.
This study has confirmed the significant prognostic role of PAK4 level in cervical cancer patients and has recognized the regulatory role in cervical cancer progression. Moreover, our study has indicated that PAK4 also confers the chemoresistance of cervical cancer cells in a PI3K/Akt-dependent way. Thus, our study indicates PAK4 as a promising marker for cervical cancer treatment.
Cervical cancer records the third most common women malignancy, with an estimated global incidence of over 500,000 new cases , and leads secondly the death cause of women world widely, with an estimated 530,000 deaths per year . Multistep processes and molecular markers have been confirmed to be involved in the tumorigenesis, invasiveness of cervical cancers . Although radiotherapy, chemotherapy and surgery have recently been standardized for patients with cervical cancer, clinical outcomes still vary significantly. Therefore, it is important to expand the knowledge of the molecular pathways and markers of cervical cancers to identify prognostic markers and to improve therapeutic strategies. Cervical cancer is clinically staged according to such prognostic factors as clinical stage at diagnosis time, tumor size, vascular invasion, and adjacent/lymphatic metastasis. And such staging define the treatment option for single surgery or for multidisciplinary treatments with either concurrent chemoradiation or with neoadjuvant chemotherapy followed by surgery .
The etiology of cervical cancer has been largely attributed to infection of human papillomavirus (HPV) [5, 6]. However, HPV infection does not necessarily lead to such cancer . And accumulating studies gaining insight into other molecular characterization of it have identified many novel biological factors, which directly or indirectly regulate cell cycle, apoptosis, angiogenesis, or invasive or metastatic potential of cervical cancers [8–10]. Moreover, since the therapeutic resistance is a common phenomenon in cervical cancers, particularly in patients with advanced, recurrent, and metastatic disease . Thus, biomarkers of proteins [11, 12] and microRNAs [13–15], which are associated with the chemo- radio-resistance of cervical cancer have been proposed to be promising and to facilitate the definition for cervical cancer treatment options.
The small GTPases, i.e. Ras, Rho, Rac and Cdc42 are a family of G-proteins in the cytosol function independently as a hydrolase enzyme (bind and hydrolyze guanosine triphosphate (GTP)). p21-activated kinases (PAKs) are a family of serine/threonine protein kinases (PAK1-6) which are best characterized downstream effectors of Rac and Cdc42 . PAKs have increasingly recognized to be overexpressed and/or hyperactivated in several human tumors such as breast cancer, colon cancer, lung cancer and gastric cancer [17, 18], closely correlating with cancer development. PAKs are significantly relevant to tumorigenesis by regulating the Ras-induced cell cycle progression and metabolism [19, 20], epithelial–mesenchymal transition  and angiogenesis . Besides, PAK4 has been recognized to modulate the cancer migration and invasion via interacting with Met  or with DGCR6L . Moreover, PAK4 has recently been found to confer cisplatin resistance in gastric cancer cells  or in glioma . However, the oncogenic role of PAK4 in cervical cancer has not been reported.
This study was designed to explore the potential prognosis value of PAK4 in cervical cancer, and then to investigate the regulatory role of PAK4 in the cisplatin resistance in cervical cancer cells. Our results demonstrate that PAK4 is closely associated with the development and progression of cervical cancer and confers cisplatin resistance in cervical cancer cells.
Cervical cancer patients
Association PAK4 expression with clinicopathological features of human cervical cancer
No. (n = 95)
Tumor size (cm)
Cell culture and treatment
Human cervical cancer Hela and Caski cells were purchased from American Type Culture Collection (ATCC) (Rockville, MD, USA) and were cultured in Dulbecco’s Modified Eagle Medium (DMEM) (for Hela cells) or RPMI-1640 medium (for Caski cells), which was supplemented with 10 % fetal bovine serum (FBS) (GIBCO, Rockville, MD, USA), with 100 U/mL penicillin and 100 μg/mL streptomycin (CSPC, Shijiazhuang, China). Cells were incubated in a humidified atmosphere at 37 °C in 5 % CO2. For the cisplatin (Sigma-Aldrich, St. Louis, MO, USA) treatment, 85 % or higher confluent Hela or Caski cells were updated with DMEM or RPMI-1640 medium supplemented with 2 % FBS, and with 5 μM (for Hela cells) or 10 μM (for CaSki cells) cisplatin for 12, 24 or 48 h; For the PAK4 overexpression, the open reading frame (ORF) of PAK4 (NM_005884.3) was amplified by PCR with Phusion polymerase (New England Biolabs, Ipswich, MA, USA) and with the primers (Forward primer: 5′-ATG TTT GGG AAG AGG AAG AAG C-3′ and Reverse primer: 5′-TCA TCT GGT GCG GTT CTG GCG-3′). The ORF sequence was then cloned into the pcDNA3.1(+) vector (Invitrogen, Carlsbad, CA, USA), with Hind III (New England BioLabs, Beverly, MA, USA) and BamH I (New England BioLabs, Beverly, MA, USA) as restriction enzymes, and with the chloramphenicol acetyltransferase (CAT) as a control for PAK4. Hela or Caski cells with more than 85 % confluence were transfected with the recombinant pcDNA3.1(+)-PAK4 or pcDNA3.1(+)-Con plasmid with Lipofectamine 2000 (Invitrogen, Carlsbad, CA, USA). For the PAK4 knockout, the PAK4-specific siRNA (siRNA-PAK4) or siRNA-Con (Santa Cruz Biotechnology, Santa Cruz, CA, USA) with 25 or 50 nM were transfected with Lipofectamine RNAiMax (Invitrogen, Carlsbad, CA, USA) into the Hela or Caski cells to abrogate the HIWI expression. Phosphoinositide 3-kinase/ RAC-alpha serine/threonine-protein kinase (PI3K/Akt) inhibitor, LY294002 (Thermo Scientific, Rockford, IL, USA) was utilized with 10 or 20 nM (Hela cells) or with 15 or 30 nM (Caski cells) to block the PI3K/Akt pathway.
Quantitative analysis of PAK4 with RT-qPCR
To investigate the expression of PAK4 on mRNA level, Real-time quantitative polymerase chain reaction (RT-qPCR) was performed with PAK4-specific primers (Forward primer: 5′-CAG GGA AGG CAG GCA GCC GA-3′ and Reverse primer: 5′-CCT GTC ACC ACT GCC GCC AC-3′) with the mRNA samples from cervical cancer tissue specimens and cervical cancer Hela or Caski cells. mRNA samples were prepared from the cervical cancer tissues, peritumor tissues, or from Hela or Caski cells with the TRIzol reagent (Invitrogen, Carlsbad, CA, USA) according to the product’s manual, were supplemented with Rnase inhibitor (Takara, Tokyo, Japan), and were stored at −80 °C before use. RT-qPCR procedure was performed with SYBR green OneStep RT-PCR Kit (Takara, Tokyo, Japan) according to the manufacturer’s manual. PAK mRNA level was calculated and was presented as the relative level of PAK4 to β-actin (as control) by ∆∆ Ct method .
Cell viability assay with MTT
Cell viability was examined with methyl thiazolyl tetrazoliym assay (MTT). Briefly, Hela or Caski cells which were plated in 96-well plates with 85-90 % confluence post the treatment with cisplatin, post the plasmid or siRNA transfection or (and) post the treatment with LY294002 were updated with 50 μl MTT solution for a incubation at 37 °C for 2 h. Then cells were updated with 150 μl DMSO was added to dissolve the precipitate completely at room temperature. The optical density was measured at 570 nm using a spectrophotometer (Bio-Rad, Hercules, CA, USA).
Western blot analysis
Hela or Caski cells, post treatment, were harvested with a cell scraper and were homogenized in an ice-cold Cell lysis buffer (Bio-Rad, Hercules, CA, USA). Cellular lysates were centrifugated with 12,000 × g for 30 min at 4 °C, and the supernatant was collected. Protein samples were separated with 10 % (w/v) SDS-PAGE gel and were transferred to a nitrocellulose membrane (Millipore, Bedford, MA, USA). For analysis of PAK4, AKT with or without phosphorylated Ser473, blots were incubated with rabbit polyclone antibody against human PAK4 (diluted with 5 % BSA to 1: 500, PA5-15120, Thermo Scientific, Rockford, IL, USA), against PAK4 with phosphorylated Ser474 (diluted with 5 % BSA to 1: 500, PA5-17636, Thermo Scientific, Rockford, IL, USA), against AKT with (diluted with 5 % BSA to 1: 500, No. 4685, Cell Signaling Technology Inc., Danvers, MA, USA) or without phosphorylated Ser473 (diluted with 5 % BSA to 1: 500, No. 4060, Cell Signaling Technology Inc., Danvers, MA, USA) or against β-actin (diluted with 5 % BSA to 1: 1000, No.1320, Sinobio, Beijing, China) respectively. Then, the specific binding on the membrane was probed with Horseradish Peroxidase (HRP)-labeled anti-rabbit secondary antibody (diluted with 5 % BSA to 1: 1000, #7071, Cell Signaling Technology Inc., Danvers, MA, USA) and with enhanced chemiluminescence (ECL) detection kit (Amersham Pharmacia Biotech, Amersham, UK).
Statistical analysis was conducted using the GraphPad Prism (GraphPad Software, La Jolla, CA, USA). The chisquare test was used to evaluate the association of PAK4 overexpression with clinic-pathological characteristics. Kaplan–Meier analysis and log-rank test were utilized to curve the overall survical of cervical cancer patients. The univariate Cox regression was performed to examine the influence of each clinic-pathological characteristic on patient survival. And the multivariate analysis with Cox proportional hazards model for each variable that were significant in the univariate analysis. P < 0.05 or less was considered as statistically significant.
Upregulated PAK4 in cervical cancer, correlating with the cancer’s malignance
To recognize the association between the PAK4 high expression and each clinic-pathological characteristic, we analyzed the statistical difference in age, tumor size, HPV infection, tumor histology, FIGO stage, lymph node metastasis, distant metastasis and histological grade between the high PAK4 and low groups with chi-square test. And it was indicated in table 1 that there was no significant difference in age, tumor size, HPV infection, or tumor histology between the two groups of patients. However, the high PAK4 expression was markedly associated with the FIGO stage, lymph node metastasis, distant metastasis and histological grade of these cervical cancer patients. Those patients with higher FIGO stage (p = 0.00822), with lymph node (p = 0.00525) or distant (p = 0.02105) metastasis, or with poor histological grade (p = 0.03464) presented significantly higher level of PAK4 mRNA in their cervical cancer specimens.
High PAK4 expression associates with poor prognosis to cervical cancer patients
Univariate analysis of prognostic factors in cervical cancer patients
95 % Confidence Interval
< 65 vs ≥ 65
Tumor size (cm)
< 4 vs ≥4
Positive vs Negative
Squamous vs Others
Ib-IIa vs IIb-IIIa
Positive vs Negative
Positive vs Negative
Poor vs Well/moderate
High vs Low
Multivariate analysis of prognostic factors in cervical cancer patients
95 % Confidence Interval
Ib-IIa vs IIb-IIIa
Positive vs Negative
Poor vs Well/moderate
High vs Low
PAK4 confers cisplatin resistance in cervical cancer cells in vitro
PI3K/Akt-dependent pathway is implicated in the PAK4-confered cisplatin resistance
PAK4 activation/upregulation has been recognized to be associated with the malignance in various types of human cancers, such as cancers in ovarium , gaster [28, 18], hypar . The prognostic value and therapeutic potential of PAK4 has been confirmed in ovarian cancer . PAK4 has been indicated to correlate with poorer survival in patients with metastatic gastric cancer . Therefore, these findings suggested that PAK4 is indicative for the clinical progression and prognosis of GC. In the present study, we confirmed the upregulation of PAK4 in the tumor tissues than in the peritumor tissues in 93 cases of cervical cancers; and the PAK4 upregulation was markedly associated with the FIGO stage, lymph node metastasis, distant metastasis and histological grade of these cervical cancer patients, was significantly and independently prognostic for the overall survival time of these patients.
Accumulating evidence has confirmed the mediation of PAK4 in chemoresistance in various types of cancers. Recently, PAK4 has been indicated to enhance the survival and decrease the apoptosis of prostate cancer cells following chemotherapy , and to be a predictive marker of gemcitabine sensitivity in pancreatic cancer cell lines . And in gastric cancer, overexpressed PAK4 has also been suggested to confer the resistance to capecitabine/cisplatin chemotherapy [30, 24]. In the present study, PAK4 overexpression posed marked amelioration of the viability reduction of cervical Hela and Caski cells post the cisplatin treatment, time-dependently, whereas the knockout of PAK4 aggravated the cisplatin-mediated viability reduction in both types of cells. Therefore, our study confirmed the mediation of PAK4 in the resistance to cisplatin in Hela and Caski cells. In addition, the PI3K/Akt-dependent pathway was implicated in the PAK4-confered cisplatin resistance in Hela and Caski cells. The phosphorylated AKT was significantly promoted by the cisplatin treatment in Hela and Caski cells. However, the promotion to the phosphorylated AKT was inhibited by the knockout of PAK4. On the other side, the PI3K/Akt inhibitor, LY294002 markedly deteriorated the cisplatin-mediated viability reduction of Hela and Caski cells. Thus, our results confirmed the involvement of PI3K/Akt-dependent pathway in the PAK4-confered cisplatin resistance.
In summary, this study has confirmed the significant prognostic role of PAK4 level in cervical cancer patients and has recognized the regulatory role in cervical cancer progression. High PAK4 level is correlated with the advanced stage cervical cancer, and is an independent factor for predicting the clinical prognosis of patients with cervical cancer. Moreover, our study has indicated that PAK4 also confers the chemoresistance of cervical cancer cells in a PI3K/Akt-dependent way. Thus, our study indicates PAK4 as a promising marker for cervical cancer treatment.
The present study was supported by the grant from the School of Pharmaceutical Science and Technology, Tianjin University (N2013-3).
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