Polo-like kinase 1 as a biomarker predicts the prognosis and immunotherapy of breast invasive carcinoma patients

Invasive breast carcinoma(BRCA)is associated with poor prognosis and high risk of mortality.Therefore,it is critical to identify novel biomarkers for the prognostic assessment of BRCA.Methods:The expression data of polo-like kinase 1(PLK1)in BRCA and the corresponding clinical information were extracted from TCGA and GEO databases.PLK1 expression was validated in diverse breast cancer cell lines by quantitative real-time polymerase chain reaction(qRT-PCR)and western blotting.Single sample gene set enrichment analysis(ssGSEA)was performed to evaluate immune infiltration in the BRCA microenvironment,and the random forest(RF)and support vector machine(SVM)algorithms were used to screen for the hub infiltrating cells and calculate the immunophenoscore(IPS).The RF algorithm and COX regression model were applied to calculate survival risk scores based on the PLK1 expression and immune cell infiltration.Finally,a prognostic nomogram was constructed with the risk score and pathological stage,and its clinical potential was evaluated by plotting calibration charts and DCA curves.The application of the nomogram was further validated in an immunotherapy cohort.Results:PLK1 expression was significantly higher in the tumor samples in TCGA-BRCA cohort.Furthermore,PLK1 expression level,age and stage were identified as independent prognostic factors of BRCA.While the IPS was unaffected by PLK1 expression,the TMB and MATH scores were higher in the PLK1-high group,and the TIDE scores were higher for the PLK1-low patients.We also identified 6 immune cell types with high infiltration,along with 11 immune cell types with low infiltration in the PLK1-high tumors.A risk score was devised using PLK1 expression and hub immune cells,which predicted the prognosis of BRCA patients.In addition,a nomogram was constructed based on the risk score and pathological staging,and showed good predictive performance.Conclusions:PLK1 expression and immune cell infiltration can predict post-immunotherapy prognosis of BRCA patients.

Overexpression of polo-like kinase1 predicts a poor prognosis in hepatocellular carcinoma patients

AIM： To elucidate the role of overexpressed polo-like kinasel （PLK1）in hepatocellular carcinoma （HCC）. METHODS： We prospectively collected clinicopathological, immunohistochemical and semi-quantitative reverse transcription-polymerase chain reaction （RT-PCR） data from 135 HCC patients undergoing successful hepatectomy. The correlations between PLK1 mRNA expression and clinicopathologic variables were analyzed by Mann-Whitney U test. Prognostic factors were identified by univariate and multivariate analyses. RESULTS： Immunohistochemical results showed overexpression of PLK1 was mainly found in tumor tissues compared with tumor-free tissue. A similar mRNA result was obtained by semi-quantitative RT-PCR. A total of 111 samples were positive for PLK1 mRNA expression. The positive expression was correlated with venous invasion, tumor nodules and Edmondson grade. Furthermore, 1, 3, 5-year survival rates in the positive expression group were significantly lower than the negative control group. Multivariate analysis showed that positive PLK1 expression was an independent risk factor for HCC. CONCLUSION： PLK1 could be a potential biomarker for diagnosis and therapy for HCC.

Polo-like kinase 1,a new therapeutic target in hepatocellular carcinoma

AIM： To investigate the role of polo-like kinase 1 （PLK1） as a therapeutic target for hepatocellular carcinoma （HCC）. METHODS： PLK1 gene expression was evaluated in HCC tissue and HCC cell lines. Gene knockdown with short-interfering RNA （siRNA） was used to study PLK1 gene and protein expression using real-time reverse transcription polymerase chain reaction （RT-PCR） and Western blotting, and cell proliferation using 3-（4,5-dim ethylthiazol-2-yl）-5-（3-carboxymethoxyphenyl）-2（4-sulf ophenyl）-2H-tetrazolium （MTS） and bromodeoxyuridine （BrdU） assays. Apoptosis was evaluated using the terminal deoxynucleotidyl transferase dUTP nick end label- ing （TUNEL） assay, and caspase-inhibition assay. Huh-7 cells were transplanted into nude mice and co-cultured with PLK1 siRNA or control siRNA, and tumor progres- sion was compared with controls. RESULTS： RT-PCR showed that PLK1 was overexpre- ssed 12-fold in tumor samples compared with controls, and also was overexpressed in Huh-7 cells, siRNA against PLK1 showed a reduction in PLK1 gene and protein expression of up to 96% in Huh-7 cells, and a reduction in cell proliferation by 68% and 92% in MTS and BrdU cell proliferation assays, respectively. There was a 3-fold increase in apoptosis events, and TUNEL staining and caspase-3 assays suggested that this was caspase-independent. The pan-caspase inhibitor Z-VAD-FMK was unable to rescue the apoptotic cells. Immnofluorescence co-localized endonuclease-G to fragmented chromosomes, implicating it in apoptosis. Huh-7 cells transplanted subcutaneously into nude mice showed tumor regression in siPLKl-treated mice, but not in controls. CONCLUSION： Knockdown of PLK1 overexpression in HCC was shown to be a potential therapeutic target, leading to apoptosis through the endonuclease-G path- way.

Dual targeting of Polo-like kinase 1 and baculoviral inhibitor of apoptosis repeat-containing 5 in TP53-mutated hepatocellular carcinoma

BACKGROUND Hepatocellular carcinoma(HCC),often diagnosed at advanced stages without curative therapies,is the fifth most common malignant cancer and the second leading cause of cancer-related mortality.Polo-like kinase 1(PLK1)is activated in the late G2 phase of the cell cycle and is required for entry to mitosis.Interestingly,PLK1 is overexpressed in many HCC patients and is highly associated with poor clinical outcome.Baculoviral inhibitor of apoptosis repeatcontaining 5(BIRC5)is also highly overexpressed in HCC and plays key roles in this malignancy.AIM To determine the expression patterns of PLK1 and BIRC5,as well as their correlation with p53 mutation status and patient clinical outcome.METHODS The expression patterns of PLK1 and BIRC5,and their correlation with p53 mutation status or patient clinical outcome were analyzed using a TCGA HCC dataset.Cell viability,cell apoptosis,and cell cycle arrest assays were conducted to investigate the efficacy of the PLK1 inhibitors volasertib and GSK461364 and the BIRC5 inhibitor YM155,alone or in combination.The in vivo efficacy of volasertib and YM155,alone or in combination,was assessed in p53-mutated Huh7-derived xenograft models in immune-deficient NSIG mice.RESULTS Our bioinformatics analysis using a TCGA HCC dataset revealed that PLK1 and BIRC5 were overexpressed in the same patient subset and their expression was highly correlated.The overexpression of both PLK1 and BIRC5 was more frequently detected in HCC with p53 mutations.High PLK1 or BIRC5 expression significantly correlated with poor clinical outcome.PLK1 inhibitors(volasertib and GSK461364)or a BIRC5 inhibitor(YM155)selectively targeted Huh7 cells with mutated p53,but not HepG2 cells with wild-type p53.The combination treatment of volasertib and YM155 synergistically inhibited the viability of Huh7 cells via apoptotic pathway.The efficacy of volasertib and YM155,alone or in combination,was validated in vivo in a Huh7-derived xenograft model.CONCLUSION PLK1 and BIRC5 are highly co-expressed in p53-mutated HCC and inhibition of both PLK1 and BIRC5 synergistically compromises the viability of p53-mutated HCC cells in vitro and in vivo.

丝/苏氨酸蛋白激酶Plk1研究进展

Plk1是一类从酵母到人类都高度保守的丝氨酸/苏氨酸蛋白激酶。Plk1与不同的细胞周期检查点的精密调控有关,从而确保了细胞周期事件按照严格的时间和顺序正常进行。Plk1在增殖活跃的细胞中呈高水平表达,Plk1的高度表达和肿瘤患者的低存活率之间具有显著的统计相关性。Plk1可能是非常有效的抗癌药物设计的靶点。目前已有几种Plk1的小分子抑制剂在体内外的实验中显示出了良好的应用前景。

中心体Plk1在儿童急性白血病中的表达及其意义

目的研究Polo-like kinase1(Plk1)在儿童急性白血病骨髓细胞中的表达水平。方法采用免疫组化法检测Plk1在儿童急性白血病骨髓细胞中的表达水平。结果 30例急性非淋巴细胞白血病(acute non-lymphoblastic Ieukemia,ANLL)及30例急性淋巴细胞白血病(acute lymphoblastic leukemia,ALL)儿童患者与19例正常儿童(normal,N)骨髓细胞比较,Plk1表达有显著性差异(χ2=43.947,P<0.01),在ANLL及ALL中表达水平明显高于正常儿童。结论 Plk1在儿童急性白血病中呈异常高表达,可能成为白血病治疗的有效靶点及重要标志物。

ATP非竞争性的Plk1抑制剂研究进展

Polo样激酶1(Plk1)是一种丝/苏氨酸蛋白激酶,在有丝分裂中起着重要作用。目前进入临床的Plk1抑制剂大部分是作用于ATP结合口袋的,此类ATP竞争性抑制剂活性高,但选择性差,易交叉耐药。因此,ATP非竞争性的抑制剂受到关注。本文阐述了ATP非竞争性的Plk1抑制剂的研究进展。

Polo-like kinase 1短发卡RNA重组腺病毒载体构建及其生物学应用

目的构建针对人类Polo-like kinase1（Plk1）基因的短发卡RNA（shRNA）真核表达载体，并进行腺病毒包被。方法设计并合成含有小发夹结构的Plk1 shRNA对应模板序列，退火并与pYr-1．1载体重组质粒；通过LR体外同源重组将pYr-1．1-Plk1—shRNA表达框构建至pAd—DEST腺病毒表达载体上；包装重组腺病毒；感染人类胰腺癌细胞BxPC-3验证干扰效率。实验分3组：对照组（Control）、空载组[rAd-增强绿色荧光蛋白（tAd—EGFP）]、实验组（rAd—shPlk1），实时定量反转录聚合酶链反应（RT-qPCR）和Western blot检测Plk1基因的表达，流式细胞术检测细胞周期的变化及对细胞凋亡的影响。结果腺病毒感染BxPC-3细胞后，RT-qPCR检测Plk1 mRNA表达量：对照组1．047±0．315、空载组1．121±0．199、实验组0．119±0．050；Western blot检测Plk1蛋白表达量：对照组0．760±0．088、空载组0．743±0．101、实验组0．050±0．043，实验组较对照组及空载组Plk1 mRNA和蛋白水平均明显降低（P〈0．01）。流式细胞术检测G2期细胞比例：对照组6．077±0．056、空载组6．533±1．644、实验组33．427±7．774，实验组G：期细胞数比例显著高于空载组和对照组（P〈0．01）。感染24h后实验组的细胞凋亡率明显高于空载组和对照组（P〈0．01）。结论成功构建包被有Plk1 shRNA的腺病毒表达载体，且重组腺病毒载体可以抑制Plk1基因的表达，引起细胞周期G2／M期停滞和促进细胞凋亡。

MCC1019,a selective inhibitor of the Polo-box domain of Polo-like kinase 1 as novel,potent anticancer candidate

Polo-like kinase(PLK1) has been identified as a potential target for cancer treatment.Although a number of small molecules have been investigated as PLK1 inhibitors, many of which showed limited selectivity. PLK1 harbors a regulatory domain, the Polo box domain(PBD), which has a key regulatory function for kinase activity and substrate recognition. We report on 3-bromomethylbenzofuran-2-carboxylic acid ethyl ester(designated: MCC1019) as selective PLK1 inhibitor targeting PLK1 PBD. Cytotoxicity and fluorescence polarization-based screening were applied to a library of 1162 drug-like compounds to identify potential inhibitors of PLK1 PBD. The activity of compound MC1019 against the PLK1 PBD was confirmed using fluorescence polarization and microscale thermophoresis.This compound exerted specificity towards PLK1 over PLK2 and PLK3. MCC1019 showed cytotoxic activity in a panel of different cancer cell lines. Mechanistic investigations in A549 lung adenocarcinoma cells revealed that MCC1019 induced cell growth inhibition through inactivation of AKT signaling pathway, it also induced prolonged mitotic arrest—a phenomenon known as mitotic catastrophe, which is followed by immediate cell death via apoptosis and necroptosis. MCC1019 significantly inhibited tumor growth in vivo in a murine lung cancer model without affecting body weight or vital organ size, and reduced the growth of metastatic lesions in the lung. We propose MCC1019 as promising anti-cancer drug candidate.

Effect of antisense RNA targeting polo-like kinase 1 on cell cycle and proliferation in A549 cells

Background Expression of polo-like kinase 1 (Plk1) is elevated in lung cancer and has been proposed as having prognostic value and related to resistance to chemotherapy and radiation. In addition, Plk1 has several functions in mitotic progression. In this study, the authors investigated t he effect of Plk1 depletion on cell cycle progression and proliferation in A549 cells, a lung cancer cell line.Methods A recombinant plasmid containing antisense RNA targeting Plk1 (pcDNA3-Plk1) was transfected into A549 cells. Reverse transcription-polymerase chain reaction and Western blot were used to examine Plk1 gene expression. Cell proliferation was evaluated by direct cell counting and bromodeoxyuridine (BrdU) labelling. Cell cycle and apoptosis were examined by flow cytometry. Expression of α-tubulin was detected by immunofluorescence, and the inhibition rate (IR) by chemotherapeutic agents was determined by 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl-tetrazolium bromide assay.Results After transfection into A549 cells, pcDNA3-Plk1 reduced Plk1 mRNA by 46.75% for 24 hours and by 61.84% for 48 hours. Plk1 protein was significantly decreased simultaneously (P<0.05). Abnormal morphological changes of cells and growth inhibition were observed in pcDNA3-Plk1 transfected groups. The BrdU labelling index was 25.59% 48 hours after transfection, which was significantly lower than that of the control groups (P<0.05). Forty-eight hours after transfection, there showed absence of microtubule polymerization and spindle abnormalities in staining for α-tubulin. A549 cells showed a strong G 2/M arrest and apoptosis 72 hours post transfection. IR of vinorelbine in pcDNA3-Plk1 transfected groups was significantly higher than that of the other groups (P<0.05, respectively).Conclusions Plk1 depletion interferes with spindle formation, induces cell cycle arrest and apoptosis, and consequently inhibits cell proliferation in A549 cells. Moreover, it sensitizes lung cancer cells to chemotherapy.

Polo-like kinase 1,on the rise from cell cycle regulation to prostate cancer development

Polo-like kinase 1(Plk1),a well-characterized member of serine/threonine kinases Plk family,has been shown to play pivotal roles in mitosis and cytokinesis in eu-karyotic cells.Recent studies suggest that Plk1 not only controls the process of mitosis and cytokinesis,but also,going beyond those previously described functions,plays critical roles in DNA replication and Pten null prostate cancer initiation.In this review,we briefly summarize the functions of Plk1 in mitosis and cytokinesis,and then mainly focus on newly discov-ered functions of Plk1 in DNA replication and in Pten-null prostate cancer initiation.Furthermore,we briefly introduce the architectures of human and mouse pros-tate glands and the possible roles of Plk1 in human prostate cancer development.And finally,the newly chemotherapeutic development of small-molecule Plk1 inhibitors to target Plk1 in cancer treatment and their translational studies are also briefly reviewed.

Diversity evolution and jump of Polo-like kinase 1 inhibitors

Polo-like kinase 1 （Plkl）, a member of a family of serine/threonine kinases, is an attractive target for the development of anti- cancer drugs because it is involved in the regulation of cell-cycle progression and cytokinesis. This kinase provides two pock- ets for developing Plkl inhibitors： the N-terminal catalytic domain （NCD） and the polo-box domain （PBD）. For both of the two pockets, some natural products were identified as Plkl inhibitors and some synthetic Plkl inhibitors were developed by mimicking ATP and phosphopeptides, natural products binding to NCD and PBD respectively. This article not only reviews the progression of Plkl inhibitors binding to these two pockets, but also discusses diversity evolution and jump in the process of drug development using Plkl inhibitors as examples and how they impact on drug design and pharmacopbore modeling.

Aurora B kinase activation requires survivin priming phosphorylation by PLK1

During cell division,chromosome segregation is orchestrated by the interaction of spindle microtubules with the centromere.Accurate attachment of spindle microtubules to kinetochore requires the chromosomal passenger of Aurora B kinase complex with borealin,INCENP and survivin(SUR).The current working model argues that SUR is responsible for docking Aurora B to the centromere whereas its precise role in Aurora B activation has been unclear.Here,we show that Aurora B kinase activation requires SUR priming phosphorylation at Ser20 which is catalyzed by polo-like kinase 1(PLK1).Inhibition of PLK1 kinase activity or expression of non-phosphorylatable SUR mutant prevents Aurora B activation and correct spindle microtubule attachment.The PLK1-mediated regulation of Aurora B kinase activity was examined in real-time mitosis using fluorescence resonance energy transfer-based reporter and quantitative analysis of native Aurora B substrate phosphorylation.We reason that the PLK1-mediated priming phosphorylation is critical for orchestrating Aurora B activity in centromere which is essential for accurate chromosome segregation and faithful completion of cytokinesis.

Transferrin-guided intelligent nanovesicles augment the targetability and potency of clinical PLK1 inhibitor to acute myeloid leukemia

Acute myeloid leukemia(AML)remains a most lethal hematological malignancy,partly because of its slow development of targeted therapies compared with other cancers.PLK1 inhibitor,volasertib(Vol),is among the few molecular targeted drugs granted breakthrough therapy status for AML;however,its fast clearance and dose-limiting toxicity greatly restrain its clinical benefits.Here,we report that transferrin-guided polymersomes(TPs)markedly augment the targetability,potency and safety of Vol to AML.Vol-loaded TPs(TPVol)with 4%trans-ferrin exhibited best cellular uptake,effective down-regulation of p-PLK1,p-PTEN and p-AKT and superior apoptotic activity to free Vol in MV-4-11 leukemic cells.Intravenous injection of TPVol gave 6-fold higher AUC than free Vol and notable accumulation in AML-residing bone marrow.The efficacy studies in orthotopic MV-4-11 leukemic model demonstrated that TPVol significantly reduced leukemic cell proportions in periphery blood,bone marrow,liver and spleen,effectively enhanced mouse survival rate,and impeded bone loss.This transferrin-guided nano-delivery of molecular targeted drugs appears to be an interesting strategy towards the development of novel treatments for AML.

The substrates of Plk1, beyond the functions in mitosis

Polo-like kinase 1(Plk1)is a key regulator of cell division in eukaryotic cells.In this short review,we briefly summarized the well-established functions modulated by Plk1 during mitosis.Beyond mitosis,we focused mainly on the unexpected processes in which Plk1 emerges as a critical player,including microtubule dynamics,DNA replication,chromosome dynamics,p53 regulation,and recovery from the G2 DNA-damage checkpoint.Our discussion is mainly based on the critical substrates targeted by Plk1 during these cellular events and the functional significance associated with each phosphorylation event.

Methylation of PLK1 by SET7/9 ensures accurate kinetochore–microtubule dynamics

Faithful segregation of mitotic chromosomes requires bi-orientation of sister chromatids, which relies on the sensing of correct attachments between spindle microtubules and kinetochores. Although the mechanisms underlying PLK1 activation have been extensively studied, the regulatory mechanisms that couple PLK1 activity to accurate chromosome segregation are not well understood. In particular, PLK1 is implicated in stabilizing kinetochore–microtubule attachments, but how kinetochore PLK1 activity is regulated to avoid hyperstabilized kinetochore–microtubules in mitosis remains elusive. Here, we show that kinetochore PLK1 kinase activity is modulated by SET7/9 via lysine methylation during early mitosis. The SET7/9-elicited dimethylation occurs at the Lys191 of PLK1, which tunes down its activity by limiting ATP utilization. Overexpression of the non-methylatable PLK1 mutant or chemical inhibition of SET7/9 methyltransferase activity resulted in mitotic arrest due to destabilized kinetochore–microtubule attachments. These data suggest that kinetochore PLK1 is essential for stable kinetochore–microtubule attachments and methylation by SET7/9 promotes dynamic kinetochore–microtubule attachments for accurate error correction. Our findings define a novel homeostatic regulation at the kinetochore that integrates protein phosphorylation and methylation with accurate chromosome segregation for maintenance of genomic stability.

Polo样激酶1在肾癌组织中的表达及其抑制剂BI2536对肾癌细胞株A498增殖的影响

目的 探讨Polo样激酶1（polo-like kinase 1,PLK1）在肾透明细胞癌及其癌旁组织中的表达情况,以及PLK1抑制剂BI2536对肾透明细胞癌A498细胞增殖的影响.方法 收集2013年1月至2014年12月12例肾癌根治手术标本（肾癌组）.男7例,女5例.年龄41～68岁,平均49岁.肿瘤均为单发,左肾癌5例,右肾癌7例,肿瘤最大径2.1～5.3 cm,无局部及远处转移.所有患者术前未行放、化疗,术后病理诊断均为透明细胞癌.同时收集距离肿瘤2 cm的癌旁组织作为对照组,病理检查证实无癌变.利用蛋白质印迹法检测癌组织及其癌旁组织中的PLK1蛋白的表达情况,并进行定量分析.采用流式细胞学技术分别测定0、20、40、60 μg,/L的PLK1抑制剂BI2536作用于肾透明细胞癌A498细胞48 h后对其增殖的影响.结果 PLK1在肾癌组和对照组的表达量分别为0.74±0.2和0.21-0.13,差异有统计学意义（P=0.02）.浓度0、20、40、60 μg/L BI2536作用48 h后,阻滞于G2/M期的A498细胞百分比分别为（10.28±0.47）％、（14.35 ±0.85）％、（20.49±0.78）％、（23.90±0.54）％,随着BI2536浓度的增加,阻滞于G2/M期的A498细胞比例增多（P＜0.05）.结论 PLK1在肾透明细胞癌组织中高表达,PLK1抑制剂BI2536能够抑制肾透明细胞癌细胞的增殖.

Novel molecular targets in hepatocellular carcinoma

Globally,hepatocellular carcinoma(HCC)is a leading cause of cancer and cancerrelated deaths.The therapeutic efficacy of locoregional and systemic treatment in patients with advanced HCC remains low,which results in a poor prognosis.The development of sorafenib for the treatment of HCC has resulted in a new era of molecular targeted therapy for this disease.However,the median overall survival was reported to be barely higher in the sorafenib treatment group than in the control group.Hence,in this review we describe the importance of developing more effective targeted therapies for the management of advanced HCC.Recent investigations of molecular signaling pathways in several cancers have provided some insights into developing molecular therapies that target critical members of these signaling pathways.Proteins involved in the Hedgehog and Notch signaling pathways,Polo-like kinase 1,arginine,histone deacetylases and Glypican-3 can be potential targets in the treatment of HCC.Monotherapy has limited therapeutic efficacy due to the development of inhibitory feedback mechanisms and induction of chemoresistance.Thus,emphasis is now on the development of personalized and combination molecular targeted therapies that can serve as ideal therapeutic strategies for improved management of HCC.

A combination therapy for KRAS-mutant lung cancer by targeting synthetic lethal partners of mutant KRAS

The KRAS gene is frequently mutated in multiple cancer types,but it fell off the drug discovery radar for many years because of its inherent "undruggable" structure and undefined biological properties.As reported in the paper entitled "Suppression of KRas-mutant cancer through the combined inhibition of KRAS with PLK1 and ROCK" in Nature Communications,we performed a synthetic lethal screening with a combinatorial strategy on a panel of clinical drugs;we found that combined inhibition of polo-like kinase 1 and RhoA/Rho kinase markedly suppressed tumor growth in mice.An increase in the expression of the tumor suppressor P21^(WAF1/CIP1) contributed to the synergistic mechanism of the combination therapy.These findings open a novel avenue for the treatment of KRAS-mutant lung cancer.

Cytokinesis and cancer:Polo loves ROCK'n' Rho(A)

Cytokinesis is the last step of the M （mitosis） phase, yet it is crucial for the faithful division of one cell into two. Cytokinesis failure is often associated with cancer. Cytoldnesis can be morphologically divided into four steps： cleavage furrow initiation, cleavage furrow ingression, midbody formation and abscission. Molecular studies have revealed that RhoA as well as its regulators and effectors are im- portant players to ensure a successful cytokinesis. At the same time, Polo-like kinase 1 （Plkl） is an important kinase that can target many substrates and carry out different functions during mitosis, including cytokinesis. Recent studies are beginning to unveil a closer tie be- tween Plkl and RhoA networks. More specifically, Plkl phosphorylates the centralspindlin complex Cyk4 and MKLPI/CHO1, thus re- cruiting RhoA guanine nucleotide-exchange factor （GEF） Ect2 through its phosphopeptide-binding BRCT domains. Ect2 itself can be phosphorylated by Plkl in vitro. Plkl can also phosphorylate another GEF MyoGEF to regulate RhoA activity. Once activated, RhoA-GTP will activate downstream effectors, including ROCK1 and ROCK2. ROCK2 is among the proteins that associate with Plkl Polo-binding domain （PBD） in a large proteomic screen, and Plkl can phosphorylate ROCK2 in vitro. We review current understandings of the interplay between Plkl, RhoA proteins and other proteins （e.g., NudC, MKLP2, PRC 1, CEP55） involved in cytokinesis, with particular emphasis of its clinical implications in cancer.