Identification and cellular localization of human PFTAIRE1

PFTK1 kinase regulates axogenesis during development via RhoA activation

BACKGROUND

PFTK1/Eip63E is a member of the cyclin-dependent kinases (CDKs) family and plays an important role in normal cell cycle progression. Eip63E expresses primarily in postnatal and adult nervous system in Drosophila melanogaster but its role in CNS development remains unknown. We sought to understand the function of Eip63E in the CNS by studying the fly ventral nerve cord during development.

RESULTS

Our results demonstrate that Eip63E regulates axogenesis in neurons and its deficiency leads to neuronal defects. Functional interaction studies performed using the same system identify an interaction between Eip63E and the small GTPase Rho1. Furthermore, deficiency of Eip63E homolog in mice, PFTK1, in a newly generated PFTK1 knockout mice results in increased axonal outgrowth confirming that the developmental defects observed in the fly model are due to defects in axogenesis. Importantly, RhoA phosphorylation and activity are affected by PFTK1 in primary neuronal cultures. We report that GDP-bound inactive RhoA is a substrate of PFTK1 and PFTK1 phosphorylation is required for RhoA activity.

CONCLUSIONS

In conclusion, our work establishes an unreported neuronal role of PFTK1 in axon development mediated by phosphorylation and activation of GDP-bound RhoA. The results presented add to our understanding of the role of Cdks in the maintenance of RhoA-mediated axon growth and its impact on CNS development and axonal regeneration.

Hsa_circRNA_102229 facilitates the progression of triple-negative breast cancer via regulating the miR-152-3p/PFTK1 pathway

BACKGROUND

Increasing evidence has suggested that circular RNAs (circRNAs) may act as an important regulatory factor in tumor progression. However, how circRNAs exert their functions in triple-negative breast cancer (TNBC) remains not clearly understood.

METHODS

First, circRNA microarrays were conducted to identify aberrantly expressed circRNAs in TNBC tissues. Kaplan-Meier survival analysis was conducted to calculate the correlation between the level of hsa_circRNA_102229 and outcomes of patients with TNBC. The effect of hsa_circRNA_102229 and serine/threonine-protein kinase PFTAIRE 1 (PFTK1) on TNBC cells was clarified by cell counting kit-8, transwell and wound healing assays, as well as by a flow cytometry. The molecular mechanism of hsa_circRNA_102229 was clarified through bioinformatics, a dual-luciferase reporter assay, western blotting, fluorescence in situ hybridization and real-time polymerase chain reaction. Tumor xenograft experiments were performed to analyze growth and metastasis of TNBC in vivo.

RESULTS

In TNBC tissues and cells, hsa_circ_102229 was remarkably up-regulated. Patients with TNBC presenting high hsa_circ_102229 exhibited poor prognosis. Moreover, hsa_circ_102229 could promote the migration, proliferation and invasion, whereas it inhibited the apoptosis of TNBC cells. Furthermore, hsa_circ_102229 directly targeted miR-152-3p and could regulate the expression of PFTK1 by targeting miR-152-3p. Rescue assays suggested that hsa_circ_102229 may exert its function in TNBC cells by regulating PFTK1. Additionally, knockdown of hsa_circ_102229 slowed down TNBC tumorigenesis and lung metastasis in a tumor xenograft animal model.

CONCLUSIONS

Hsa_circ_102229 might serve as a competing endogenous RNA (ceRNA) to modulate PFTK1 expression via regulating miR-152-3p to affect the functions of TNBC cells. Hsa_circ_102229 acts as a newly discovered biomarker for TNBC treatment.

The anti-tumor effect of miR-539-3p on colon cancer via regulating cell viability, motility, and nude mouse tumorigenicity with CDK14 inhibition

BACKGROUND

Colon cancer is one of the major causes of morbidity and mortality worldwide. MicroRNAs (miRNAs) play important functions in the growth and metastasis of colon cancer. This study aimed to investigate the anti-tumor effect of micro ribonucleic acid 539-3p (miR-539-3p) on colon cancer via regulation of cell viability, motility, and nude mouse tumorigenicity with cyclin-dependent kinase 14 (CDK14) inhibition.

METHODS

The target relationship between miR-539-3p and CDK14 was predicted using TargetScan software, and were detected by luciferase reporter assay. Cell counting kit-8 (CCK-8) assay and flow cytometry were employed to examine cell proliferation and apoptosis. Western blotting was employed to measure the protein expression levels of p27, cleaved caspase-3, and epithelial (E)- and neural (N)-cadherin. The effect of miR-539-3p on tumor growth was evaluated by establishing a xenograft tumor model in nude mice.

RESULTS

The target relationship of CDK14 and miR-539-3p was identified as a negative regulator. Overexpression of miR-539-3p significantly inhibited SW620 and SW480 cell proliferation, promoted cell apoptosis, and suppressed cell invasion by targeting CDK14. The xenograft tumor model showed that the overexpression of miR-539-3p reduced tumor weight and volume. Immunohistochemical staining revealed that the overexpression of miR-539-3p inhibited the expression of Ki67 and E-cadherin. Additionally, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining showed that overexpression of miR-539-3p induced apoptosis.

CONCLUSIONS

Overexpression of miR-539-3p inhibited SW620 and SW480 cell proliferation, promoted cell apoptosis, and suppressed cell invasion by targeting CDK14. Therefore, miR-539-3p may be a useful diagnostic and therapeutic biomarker for colon cancer.

Downregulation of PFTK1 Inhibits Migration and Invasion of Non-Small Cell Lung Cancer

Background

PFTK1, a novel cyclin-dependent kinase, plays pivotal roles in tumorigenesis. Cell motility and invasiveness could be enhanced by PFTK1 in various tumors. However, the function of PFTK1 in NSCLC metastasis remains unclear. In this study, the potential role of PFTK1 in NSCLC metastasis was determined.

Materials and Methods

In this study, the potential function of PFTK1 in lung cancer patients was analyzed with the Kaplan–Meier plotter database. RNA interference-mediated knockdown of PFTK1 was established in two NSCLC cell lines (H1299 and 95C) to explore the role of PFTK1 in NSCLC. The efficacy of downregulation of PFTK1 was examined by Western blot and immunofluorescence. The role of PFTK1 in cell migration and invasion ability was detected by wound healing and transwell assays. The protein levels in lung cancer cells were determined by Western blot. Immunofluorescence analysis was used to evaluate the structure of filamentous actin.

Results

Overexpression of PFTK1 was associated with the poor survival prognosis in NSCLC patients. PFTK1 knockdown cells were constructed successfully. Suppression of PFTK1 significantly inhibited the cell migration and invasion in H1299 and 95C cells. Notably, after PFTK1 downregulation, the epithelial–mesenchymal transition (EMT) markers vimentin, ZEB1 and β-catenin were obviously decreased. Additionally, immunofluorescence analysis indicated that PFTK1 downregulation remarkably induced filamentous actin depolymerization.

Conclusion

In summary, PFTK1 could significantly promote lung cancer metastasis through changing EMT progress and modulating intracellular cytoskeleton F-actin expression. Taken together, our findings indicated that PFTK1 might serve as a novel therapeutic target for the inhibition of NSCLC progression.

CDK14 involvement in proliferation migration and invasion of esophageal cancer

Background

CDK14 has significant involvement in tumorigenesis of cancers including hepatocellular carcinoma, gastric carcinoma and breast cancer. In esophageal cancer, CDK14 is useful as a prognostic marker and as a predictor of response to chemotherapy. However, the exact mechanism of CDK14 n chemotherapy for esophageal squamous cell carcinoma (ESCC) has not been explored.

Methods

Western blots and immunohistochemistry (IHC) analysis were performed to analyse the expression of CDK14 in ESCC. Co-immunoprecipitation and immunofluorescence assays were used to explore the mechanism of CDK14 involvement in ESCC. Colony formation assays and proliferation assays were used to investigate the function of CDK14 in ESCC. At last, we constructed two truncated mutants of CDK14 by the PCR technology to research the functional structural domain.

Results

Western blots and IHC analysis showed that CDK14 expression was higher n tumor tissues and cell lines than that in normal tissues. IHC staining revealed that CDK14 positively correlated with clinical pathological variables of tumor size (P=0.001), tumor grade (P=0.004), Ki-67 (P=0.012) and survival (P=0.000). Immunoprecipitation and immunofluorescence assays revealed that CDK-activating kinase (CAK), namely CDK7/CCNH complex physically interacted and was collocated with CDK14 in the cell nucleus. This direct interaction increased CDK14 phosphorylation and inhibited Rb function through phosphorylation. In vitro starvation and refeeding assays demonstrated that CDK14 expression was related to proliferation of ESCC cells. Overexpression of CDK14 in Eca109 cells increased colony formation and reduced sensitivity to cisplatin. Overexpressing CDK7 with CDK14 strengthened these effects, demonstrating that CDK7 was a major component in CDK14 activation.

Conclusions

Expression of CDK14 worsened the effects of cisplatin chemotherapy by promoting ESCC proliferation.

Identification of Differentially Expressed Genes Induced by Aberrant Methylation in Oral Squamous Cell Carcinomas Using Integrated Bioinformatic Analysis

Oral squamous cell carcinoma (OSCC) is a malignant disease. Methylation plays a key role in the etiology and pathogenesis of OSCC. The goal of this study was to identify aberrantly methylated differentially expressed genes (DEGs) in OSCCs, and to explore the underlying mechanisms of tumorigenesis by using integrated bioinformatic analysis. Gene expression profiles (GSE30784 and GSE38532) were analyzed using the R software to obtain aberrantly methylated DEGs. Functional enrichment analysis of screened genes was performed using the DAVID software. Protein–protein interaction (PPI) networks were constructed using the STRING database. The cBioPortal software was used to exhibit the alterations of genes. Lastly, we validated the results with the Cancer Genome Atlas (TCGA) data. Twenty-eight upregulated hypomethylated genes and 24 downregulated hypermethylated genes were identified. These genes were enriched in the biological process of regulation in immune response, and were mainly involved in the PI3K-AKT and EMT pathways. Additionally, three upregulated hypomethylated oncogenes and four downregulated hypermethylated tumor suppressor genes (TSGs) were identified. In conclusion, our study indicated possible aberrantly methylated DEGs and pathways in OSCCs, which could improve the understanding of the underlying molecular mechanisms. Aberrantly methylated oncogenes and TSGs may also serve as biomarkers and therapeutic targets for the precise diagnosis and treatment of OSCCs in the future.

Downregulation of dual-specificity tyrosine-regulated kinase 2 promotes tumor cell proliferation and invasion by enhancing cyclin-dependent kinase 14 expression in breast cancer

Tumor progression is the main cause of death in patients with breast cancer. Accumulating evidence suggests that dual-specificity tyrosine-regulated kinase 2 (DYRK2) functions as a tumor suppressor by regulating cell survival, differentiation, proliferation and apoptosis. However, little is known about the mechanisms of transcriptional regulation by DYRK2 in cancer progression, particularly with respect to cancer proliferation and invasion. Here, using a comprehensive expression profiling approach, we show that cyclin-dependent kinase 14 (CDK14) is a target of DYRK2. We found that reduced DYRK2 expression increases CDK14 expression, which promotes cancer cell proliferation and invasion in vitro, in addition to tumorigenicity in vivo. CDK14 and DYRK2 expression inversely correlated in human breast cancer tissues. We further identified androgen receptor (AR) as a candidate of DYRK2-dependent transcription factors regulating CDK14. Taken together, our findings suggest a mechanism by which DYRK2 controls CDK14 expression to regulate tumor cell proliferation and invasion in breast cancer. Targeting of this pathway may be a promising therapeutic strategy for treating breast cancer.

MicroRNA-613 impedes the proliferation and invasion of glioma cells by targeting cyclin-dependent kinase 14

Increasing evidence has suggested that microRNAs (miRNAs) are critical regulators of tumorigenesis. MicroRNA-613 (miR-613) has recently been reported as a novel tumor-related miRNA that plays an important role in multiple cancers. However, the expression and functional significance of miR-613 in glioma remains unclear. In this study, we aimed to investigate the biological function of miR-613 in glioma. We found that miR-613 expression was frequently downregulated in glioma tissues and cell lines compared with normal controls. Overexpression of miR-613 impeded proliferation and colony formation and induced cell cycle arrest in G0/G1 phase, and also inhibited the invasive ability of glioma cells. By contrast, miR-613 inhibition had the opposite effects. Bioinformatic analysis and dual-luciferase reporter assays showed that miR-613 directly targets the 3'-untranslated region of cyclin-dependent kinase 14 (CDK14). Real-time quantitative PCR and Western blot analysis showed that CDK14 expression is negatively regulated by miR-613. In addition, miR-613 expression was inversely correlated with CDK14 expression in clinical glioma tissues. Moreover, overexpression of miR-613 decreased the protein expression of β-catenin and inhibited the activation of Wnt signaling. Importantly, the antitumor effects of miR-613 were significantly reversed by CDK14 overexpression. Overall, our results show that miR-613 inhibits glioma cell proliferation and invasion by downregulating CDK14, suggesting that miR-613 and CDK14 may serve as potential therapeutic targets for the treatment of glioma.

High expression of PFTK1 in cancer cells predicts poor prognosis in colorectal cancer

The serine/threonine-protein kinase PFTAIRE 1 (PFTK1) is a member of the cyclin‑dependent kinase family that is highly expressed in several malignant tumors, including hepatocellular carcinoma, esophageal, breast and gastric cancers, and glioma. It contributes to tumor progression and influences tumor prognosis. However, the expression and clinicopathological significance of PFTK1 in human colorectal cancer (CRC) remain to be elucidated. The present study aimed to examine the expression of PFTK1 and to evaluate the clinical significance of its expression in human CRC. Reverse transcription‑quantitative polymerase chain reaction was performed on 10 fresh CRC and 10 surrounding normal tissue samples to detect and compare the expression of PFTK1 mRNA in CRC and normal colorectal tissues. Immunohistochemistry was performed on 179 CRC tissue specimens and 47 control samples of normal colorectal lesions to characterize the expression of PFTK1 protein. Kaplan‑Meier overall survival (OS) rate and Cox regression analyses were performed to evaluate the prognosis of patients with CRC. The expression of PFTK1 mRNA in CRC tissues (1.433±0.168) was significantly higher compared with normal tissues (0.853±0.107; t=1.97 ('t' was the value obtained from quantification of the mRNA data, following a paired t‑test), P=0.008). High PFTK1 expression in cancerous cells was detected in 92 of the CRC specimens (51.40%), and high levels of PFTK1 were associated with tumor node metastasis (TNM) stage (P=0.042), tumor classification (P=0.022) and preoperative carcinoembryonic antigen (CEA) level (P<0.001). Kaplan‑Meier OS rate and Cox regression analysis revealed that high PFTK1 expression level (hazard ratio (HR)=1.999; P=0.019) was an independent prognostic factor of CRC patients. The degree of differentiation (HR, 0.368, P=0.003), TNM classification (HR, 2.118, P=0.001) and preoperative CEA level (HR, 2.302, P=0.003) were also predictors of the prognosis of patients with CRC. The present study suggested that PFTK1 may be a potential anticancer target and prognostic marker in patients with CRC.

Knockdown of PFTAIRE Protein Kinase 1 (PFTK1) Inhibits Proliferation, Invasion, and EMT in Colon Cancer Cells

PFTK1 is a member of the cyclin-dependent kinase (CDK) family and is upregulated in many types of tumors. However, its expression and role in colon cancer remain unclear. In this study, we aimed to investigate the expression and function of PFTK1 in colon cancer. Our results showed that PFTK1 was highly expressed in colon cancer cell lines. The in vitro experiments demonstrated that knockdown of PFTK1 inhibited the proliferation, migration, and invasion of colon cancer cells as well as the epithelial-to-mesenchymal transition (EMT) progress. Furthermore, knockdown of PFTK1 suppressed the expression of Shh as well as Smo, Ptc, and Gli-1 in colon cancer cells. Taken together, these results suggest that knockdown of PFTK1 inhibited the proliferation and invasion of colon cancer cells as well as the EMT progress by suppressing the Sonic hedgehog signaling pathway. Therefore, these findings reveal that PFTK1 may be a potential therapeutic target for the treatment of colon cancer.

Knockdown of PFTK1 Expression by RNAi Inhibits the Proliferation and Invasion of Human Non-Small Lung Adenocarcinoma Cells

PFTK1 (PFTAIRE protein kinase 1), also named CDK14 (cyclin-dependent kinase 14), is a member of the cell division cycle 2 (CDC2)-related protein kinase family. It is highly expressed in several malignant tumors. However, the role of PFTK1 in the progression of non-small cell lung cancer (NSCLC) is still elusive. In this study, we aimed to explore the expression and function of PFTK1 in NSCLC cells. Our results showed that PFTK1 was significantly upregulated in human NSCLC cell lines. Silencing the expression of PFTK1 inhibited the proliferation of NSCLC cells. In addition, silencing the expression of PFTK1 endowed NSCLC cells with decreased migration and invasion abilities, as well as epithelial-mesenchymal transition (EMT) progress in A549 cells. A mechanistic study showed that knockdown of PFTK1 inhibited the expression of β-catenin, cyclin D1, and c-Myc in A549 cells. In summary, we report that small interfering RNA (siRNA)-PFTK1 might inhibit the proliferation and invasion of NSCLC cells by suppressing the Wnt/β-catenin signaling pathway. Therefore, PFTK1 may represent a novel therapeutic target for the treatment of NSCLC.

Activation/Proliferation-associated Protein 2 (Caprin-2) Positively Regulates CDK14/Cyclin Y-mediated Lipoprotein Receptor-related Protein 5 and 6 (LRP5/6) Constitutive Phosphorylation

Low-density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) are co-receptors for Wnt ligands. Upon ligand binding, LRP5/6 undergo glycogen synthase kinase 3 (GSK3)/casein kinase I (CKI)-mediated phosphorylation at multiple PPP(S/T)P motifs in the intracellular domain, which is essential for canonical Wnt signal transduction. On the other hand, in the Wnt-off state, the mitosis-specific CDK14-Cyclin Y kinase complex phosphorylates Ser-1490 of LRP5/6 at G₂/M, thereby priming the receptor for Wnt-induced phosphorylation. However, it remains unclear how CDK14/Cyclin Y is recruited to LRP5/6 and whether there are other cofactors involved in this process. Previously, we identified Caprin-2 as a positive regulator of canonical Wnt signaling by promoting GSK3-depedent LRP5/6 phosphorylation upon Wnt stimulation. Here we uncovered that Caprin-2 positively regulates constitutive LRP5/6 Ser-1490 phosphorylation by complexing with CDK14/Cyclin Y. Caprin-2-mediated LRP5/6 phosphorylation is cell cycle-dependent in a pattern similar to that of CDK14/Cyclin Y-dependent LRP5/6 phosphorylation. Moreover, knockdown of Caprin-2 disrupts not only the interaction between CDK14 and Cyclin Y but also the interaction between CDK14/Cyclin Y and LRP6. Overall, our findings revealed an unrecognized role of Caprin-2 in facilitating LRP5/6 constitutive phosphorylation at G₂/M through forming a quaternary complex with CDK14, Cyclin Y, and LRP5/6.

RNAi-mediated downregulation of cyclin Y to attenuate human breast cancer cell growth

Cyclin Y (CCNY) is a newly identified PFTK1 interacting protein and has been found to be associated with the proliferation and tumorigenesis of human non-small cell lung cancer. In the present study, we analyzed the expression levels of CCNY in 65 cases of breast cancer (BC) tissues and in four BC cell lines, BT-474, MDA-MB-231, T-47D and MCF-7. Lentivirus-mediated short hairpin RNA (shRNA) was employed to knock down CCNY expression in MCF-7 and MDA-MB-231 cells. The effects of CCNY depletion on cell growth were examined by MTT, colony formation and flow cytometry assays. The results showed that immunohistochemical expression of CCNY in tumor tissues is stronger than that in normal tissues. CCNY was also expressed in all four BC cells. The knockdown of CCNY resulted in a significant reduction in cell proliferation and colony formation ability. Cell cycle analysis showed that CCNY knockdown arrested MDA-MB‑231 cells in the G0/G1 phase. Furthermore, depletion of CCNY inhibited BC cell growth via the activation of Bad and GSK3β, as well as cleavages of PARP and caspase-3 in a p53-dependent manner. Therefore, we believe that CCNY has biological effect in BC development, and its inhibition via an RNA interference lentiviral system may provide a therapeutic option for BC.

Aberrant regulation of Wnt signaling in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies in the world. Several signaling pathways, including the wingless/int-1 (Wnt) signaling pathway, have been shown to be commonly activated in HCC. The Wnt signaling pathway can be triggered via both catenin β1 (CTNNB1)-dependent (also known as “canonical”) and CTNNB1-independent (often referred to as “non-canonical”) pathways. Specifically, the canonical Wnt pathway is one of those most frequently reported in HCC. Aberrant regulation from three complexes (the cell-surface receptor complex, the cytoplasmic destruction complex and the nuclear CTNNB1/T-cell-specific transcription factor/lymphoid enhancer binding factor transcriptional complex) are all involved in HCC. Although the non-canonical Wnt pathway is rarely reported, two main non-canonical pathways, Wnt/planar cell polarity pathway and Wnt/Ca²⁺ pathway, participate in the regulation of hepatocarcinogenesis. Interestingly, the canonical Wnt pathway is antagonized by non-canonical Wnt signaling in HCC. Moreover, other signaling cascades have also been demonstrated to regulate the Wnt pathway through crosstalk in HCC pathogenesis. This review provides a perspective on the emerging evidence that the aberrant regulation of Wnt signaling is a critical mechanism for the development of HCC. Furthermore, crosstalk between different signaling pathways might be conducive to the development of novel molecular targets of HCC.

PFTK1 regulates cell proliferation, migration and invasion in epithelial ovarian cancer

PFTK1, also named Cyclin-Dependent Kinase 14 (CDK14), is a member of the cell division cycle 2 (CDC2)-related protein kinase family. It is a serine/threonine-protein kinase involved in the regulation of cell cycle progression and cell proliferation. In this study, we investigated the role of PFTK1 in epithelial ovarian cancer (EOC) development. The expression of PFTK1 was detected by Western blot and immunohistochemistry staining, both of which demonstrated that PFTK1 was overexpressed in EOC tissues and cells. Statistical analysis showed the expression of PFTK1 was associated with multiple clinicopathological factors, including tumor grade, FIGO stage, lymph node metastatis, Ki-67 expression and predicted a poor prognosis of EOC patients. With in vitro studies we found that PFTK1 expression was decreased in serum-starved ovarian cancer cells, and progressively increased after serum-re-feeding. Knocking PFTK1 down by small interfering RNA (siRNA) significantly inhibited ovarian cancer cell proliferation, migration and invasion. Taken together, our study suggested that PFTK1 played an important role in ovarian cancer development.

PFTK1 Promotes Gastric Cancer Progression by Regulating Proliferation, Migration and Invasion

PFTK1, also known as PFTAIRE1, CDK14, is a novel member of Cdc2-related serine/threonine protein kinases. Recent studies show that PFTK1 is highly expressed in several malignant tumors such as hepatocellular carcinoma, esophageal cancer, breast cancer, and involved in regulation of cell cycle, tumors proliferation, migration, and invasion that further influence the prognosis of tumors. However, the expression and physiological significance of PFTK1 in gastric cancer remain unclear. In this study, we analyzed the expression and clinical significance of PFTK1 by Western blot in 8 paired fresh gastric cancer tissues, nontumorous gastric mucosal tissues and immunohistochemistry on 161 paraffinembedded slices. High PFTK1 expression was correlated with the tumor grade, lymph node invasion as well as Ki-67. Through Cell Counting Kit (CCK)-8 assay, flow cytometry, colony formation, wound healing and transwell assays, the vitro studies demonstrated that PFTK1 overexpression promoted proliferation, migration and invasion of gastric cancer cells, while PFTK1 knockdown led to the opposite results. Our findings for the first time supported that PFTK1 might play an important role in the regulation of gastric cancer proliferation, migration and would provide a novel promising therapeutic strategy against human gastric cancer.

Knockdown of PFTK1 Inhibits the Migration of Glioma Cells

The prognosis of glioma patients is generally poor, so it is urgent to find out the underlying molecular mechanisms. PFTK1 is a member of cyclin-dependent kinases (Cdks) family and has been reported to contribute to tumor migration and invasion. In this study, we aimed to explore the expression and function in human glioma. Western blot and immunohistochemistry were used to evaluate the expression of PFTK1. PFTK1 expression was higher in glioma tissues compared with normal brain tissues, and its level was associated with the WHO grade in Western blot analysis. The suppression of PFTK1 expression by RNA interference was shown to inhibit the migration of glioma cells. Knockdown of PFTK1 increases E-cadherin expression and decreases vimentin expression. These data show that PFTK1 may participate in the pathogenic process of glioma, suggesting that PFTK1 can become a potential therapeutic strategy for gastric cancer.

Upregulated PFTK1 promotes tumor cell proliferation, migration, and invasion in breast cancer

PFTK1 was a cell division cycle 2-related serine/threonine protein kinase, which was up-regulated in breast cancer tissues and breast cancer lines. And up-regulated PFTK1 was highly associated with grade, axillary lymph node status, and Ki-67. Moreover, Kaplan-Meier curve showed that up-regulated PFTK1 was related to the poor breast carcinoma patients' overall survival. Here, we first discovered and confirmed that cyclin B was a new interacting protein of PFTK1, and the complex might increase the amount of DVL2, which triggers Wnt/β-catenin signaling pathway. Furthermore, knockdown of PFTK1 attenuated cell proliferation, anchorage-independent cell growth, and cell migration and invasion by inhibiting the transcriptional activation of β-catenin for cyclin D1, MMP9, and HEF1, whereas exogenous expression of PFTK1 might promote MDA-MB-231 cells proliferation, migration, and invasion via promoting PFTK1-DVL2-β-catenin axis. Our findings supported the notion that up-regulated PFTK1 might promote breast cancer progression and metastasis by activating Wnt signaling pathway through the PFTK1-DVL2-β-catenin axis.

PFTK1 interacts with cyclin Y to activate non-canonical Wnt signaling in hepatocellular carcinoma

PFTK1 is a Cdc2-related protein kinase that is frequently upregulated in human hepatocellular carcinoma (HCC) where it correlates with metastatic features and motile phenotypes. To understand the modulated pathway underlining the PFTK1 action, here we show a physical interaction between PFTK1 and cyclin Y (CCNY) in promoting noncanonical Wnt signaling. In HCC cells, we found PFTK1 forms a direct complex with CCNY, and together readily upregulate key components of Wnt signaling (Dvl2 and Naked1). Exogenous expression of PFTK1 and CCNY activated Rho GTPases, which are known targets of the noncanonical path. In line with Rho GTPases activation, we also found marked actin polymerizations in cells with PFTK1-CCNY co-expressions. Our findings highlight a PFTK1-CCNY complex in activating noncanonical Wnt signaling in HCC cells.

Orphan kinases turn eccentric: a new class of cyclin Y-activated, membrane-targeted CDKs

PCTAIRE kinases (PCTK) are a highly conserved, but poorly characterized, subgroup of cyclin-dependent kinases (CDK). They are characterized by a conserved catalytic domain flanked by N- and C-terminal extensions that are involved in cyclin binding. Vertebrate genomes contain three highly similar PCTAIRE kinases (PCTK1,2,3, a.k.a., CDK16,17,18), which are most abundant in post-mitotic cells in brain and testis. Consistent with this restricted expression pattern, PCTK1 (CDK16) has recently been shown to be essential for spermatogenesis. PCTAIREs are activated by cyclin Y (CCNY), a highly conserved single cyclin fold protein. By binding to N-myristoylated CCNY, CDK16 is targeted to the plasma membrane. Unlike conventional cyclin-CDK interactions, binding of CCNY to CDK16 not only requires the catalytic domain, but also domains within the N-terminal extension. Interestingly, phosphorylation within this domain blocks CCNY binding, providing a novel means of cyclin-CDK regulation. By using these functional characteristics, we analyzed "PCTAIRE" sequence containing protein kinase genes in genomes of various organisms and found that CCNY and CCNY-dependent kinases are restricted to eumetazoa and possibly evolved along with development of a central nervous system. Here, we focus on the structure and regulation of PCTAIREs and discuss their established functions.

Genome-wide association analysis of incident coronary heart disease (CHD) in African Americans: a short report

African Americans have the highest rate of mortality due to coronary heart disease (CHD). Although multiple loci have been identified influencing CHD risk in European-Americans using a genome-wide association (GWAS) approach, no GWAS of incident CHD has been reported for African Americans. We performed a GWAS for incident CHD events collected during 19 years of follow-up in 2,905 African Americans from the Atherosclerosis Risk in Communities (ARIC) study. We identified a genome-wide significant SNP (rs1859023, MAF = 31%) located at 7q21 near the PFTK1 gene (HR = 0.57, 95% CI 0.46 to 0.69, p = 1.86×10⁻⁰⁸), which replicated in an independent sample of over 8,000 African American women from the Women's Health Initiative (WHI) (HR = 0.81, 95% CI 0.70 to 0.93, p = 0.005). PFTK1 encodes a serine/threonine-protein kinase, PFTAIRE-1, that acts as a cyclin-dependent kinase regulating cell cycle progression and cell proliferation. This is the first finding of incident CHD locus identified by GWAS in African Americans.

In the United States, African Americans are at high risk for coronary heart disease (CHD). Although environmental and social factors have a role, genetic factors also contribute to CHD risk and mortality. Research to identify genetic factors for CHD susceptibility has been carried out mostly in Europeans and European Americans and little has been done in African Americans. Genome wide association studies (GWAS) provide a means to identify susceptibility loci without any a priori assumptions about the functional importance of a gene. In this study, we used GWAS to identify a novel genomic region associated with incident CHD events in African Americans from the ARIC study and replicated this finding in a large sample of African American women. This region contains several genes, including PFTK1, that regulate cell cycle progression and cell proliferation. This is the first report of a susceptibility locus for incident CHD identified by GWAS in African Americans.

A novel interplay between oncogenic PFTK1 protein kinase and tumor suppressor TAGLN2 in the control of liver cancer cell motility

The PFTK1 gene encodes a cdc2-related serine/threonine protein kinase that has been shown to confer cell migratory properties in hepatocellular carcinoma (HCC). However, the prognostic value and biological mechanism by which PFTK1 promotes HCC motility remain largely unknown. Here, we showed from tissue microarray that common upregulations of PFTK1 in primary HCC tumors (n=133/180) correlated significantly with early age onset (40 years), advance tumor grading and presence of microvascular invasion (P0.05). To understand downstream phosphorylated substrate(s) of PFTK1, phospho-proteins in PFTK1 expressing and knockdown Hep3B cells were profiled by two-dimensional-polyacrylamide gel electrophoresis mass spectrometric analysis. Protein identification of differential spots revealed β-actin (ACTB) and transgelin2 (TAGLN2) as the two most profound phosphorylated changes affected by PFTK1. We verified the presence of TAGLN2 serine phosphorylation and ACTB tyrosine phosphorylation. Moreover, reduced TAGLN2 and ACTB phosphorylations in PFTK1-suppressed Hep3B corresponded to distinct actin depolymerizations and marked inhibition on cell invasion and motility. Given that TAGLN2 is a tumor suppressor whose function has been ascribed in cancer metastasis, we examined if TAGLN2 is an intermediate substrate in the biological path of PFTK1. We showed in PFTK1-suppressed cells that knockdown of TAGLN2 over-rode the inhibitory effect on cell invasion and motility, and a recovery on actin polymerization was evident. Interestingly, we also found that unphosphorylated TAGLN2 in PFTK1-suppressed cells elicited strong actin-binding ability, a mechanism that possibly halts the actin cytoskeleton dynamics. Site-directed mutagenesis of TAGLN2 suggested that PFTK1 regulates the actin-binding affinity of TAGLN2 through the S83 and S163 residues, which if mutated can significantly affect HCC cell motility. Taken together, our data propose a novel, oncogene-tumor suppressor interplay, where oncogenic PFTK1 confers HCC cell motility through inactivating the actin-binding motile suppressing function of TAGLN2 via phosphorylation.

Phosphorylation of Caldesmon by PFTAIRE1 kinase promotes actin binding and formation of stress fibers

Caldesmon (CaD) is an actin-binding protein that is capable of stabilizing actin filaments. Phosphorylation of CaD is widely accepted in the actin cytoskeletal modeling and promotion of cell migration. In this study, we show that CaD is a downstream phosphorylation substrate of PFTK1, a novel Cdc-2-related ser/thr protein kinase. Our study stemmed from an earlier investigation where we demonstrated that PFTK1 kinase conferred cell migratory advantages in human hepatocellular carcinoma (HCC) cells. Here, we showed that PFTK1-knockdown cells exhibited much reduced CaD phosphorylation and consequently caused dissociation of CaD from the F-actin fibers. The cellular localization of CaD was also altered in the absence of PFTK1. Immunofluorescence analysis revealed that PFTK1-abrogated cells exhibited a diffused and blurred appearance of CaD localization, whereas intact co-localization with F-actins was apparent in PFTK1-expressing cells. Without the binding of CaD to actin, disappearance of actin stress fibers was also evident in PFTK1-abrogated cells. In addition, we found that CaD is also commonly up-regulated in HCC tumors when compared to adjacent non-malignant liver (P = 0.022). Taken together, our results highlight a novel biological cascade that involved the phosphorylation activation of CaD by PFTK1 kinase in promoting formation of actin stress fibers.

Why cyclin Y? A highly conserved cyclin with essential functions

Cyclin Y is one of the most highly conserved members of the cyclin superfamily of proteins, which are famous for their crucial roles in regulating the cell cycle and transcription. Despite this high degree of conservation, very little was known about Cyclin Y function prior to a handful of studies published in this past year. Cyclins typically function by activating cyclin-dependent kinases (Cdks) and one insight has come from the identification of a Cdk that is activated by Cyclin Y. Yeast two-hybrid data first linked Cyclin Y with Cdk14, known as Eip63E in Drosophila or PFTAIRE1 in vertebrates. In Drosophila, both Cyclin Y and Eip63E are essential at many stages of development, from embryogenesis to metamorphosis and null mutants show a similar spectrum of developmental defects. In cultured cells, Cyclin Y and Eip63E were shown to phosphorylate the Wg/Wnt co-receptor Arrow/LRP6 in a ligand-independent manner. Eip63E is recruited to LRP6 at the plasma membrane by interacting with Cyclin Y, which is tethered to the membrane through an N-terminal myristoylation. Cyclin Y-dependent LRP6 phosphorylation appears to prime the receptor for subsequent ligand-dependent phosphorylation and activation of the canonical Wnt signaling pathway. Interestingly, Wnt receptor phosphorylation and signaling is maximal in G₂/M when Cyclin Y is at its highest levels, suggesting that Cyclin Y may serve to entrain Wnt signaling to the cell cycle. Given the wide range of roles for Wnt signaling during development, these studies may help explain why Cyclin Y is required at several developmental stages and in turn why these proteins are so well conserved in metazoans.

PEG10 is a probable target for the amplification at 7q21 detected in hepatocellular carcinoma

DNA copy number aberrations in human hepatocellular carcinoma (HCC) cell lines were investigated using a high-density oligonucleotide microarray, and a novel amplification at the chromosomal region 7q21 was detected. Molecular definition of the amplicon indicated that PEG10 (paternally expressed gene 10), a paternally expressed imprinted gene, was amplified together with CDK14 (cyclin-dependent kinase 14; previously PFTAIRE protein kinase 1, PFTK1) and CDK6 (cyclin-dependent kinase 6). An increase in PEG10 copy number was detected in 14 of 34 primary HCC tumors (41%). PEG10, but not CDK14 or CDK6, was significantly overexpressed in 30 of 41 tumors (73%) from HCC patients, compared with their nontumorous counterparts. These results suggest that PEG10 is a probable target, acting as a driving force for amplification of the 7q21 region, and may therefore be involved in the development or progression of HCCs.

Cyclin Y, a novel membrane-associated cyclin, interacts with PFTK1

A novel cyclin, CCNY, was identified as a PFTK1 interacting protein in a yeast two-hybrid screen. The cyclin box in CCNY and the PFTAIRE motif in PFTK1 are both required for the interaction which was confirmed by in vivo and in vitro assays. Two transcripts (4 and 2kb), of CCNY were detected by Northern blot analysis and CCNY was enriched at the plasma membrane due to an N-terminal myristoylation signal. We propose that binding of CCNY to PFTK1 enhances PFTK1 kinase activity and changes its intracellular location.

Identification of PFTAIRE protein kinase 1, a novel cell division cycle-2 related gene, in the motile phenotype of hepatocellular carcinoma cells

Metastasis is a major cause of cancer morbidity and mortality in individuals with hepatocellular carcinoma (HCC), yet little is known about the underlying molecular basis. Using genetic information derived from chromosome-based comparative genomic hybridization, we have reported previously on regional chromosome 7q21-q22 gains in close association with HCC progression. In this study, we undertook cDNA microarray-based comparative genomic hybridization, to examine the 7q21-q22 region for the involved gene(s) in HCC. High-resolution mapping analysis highlighted 7 candidates, namely PFTAIRE protein kinase 1 (PFTK1), ODAG, CDK6, CAS1, PEX1, SLC25A, and PEG10, within the region. Quantitative reverse transcription (RT)-PCR evaluation further indicated upregulation of a single candidate gene, PFTK1, that correlated significantly with both advanced metastatic HCCs (P = 0.032) and tumor microvascular invasion (P = 0.012). Given that little is known about the function(s) of PFTK1, which is a novel cell division cycle (Cdc)2-related gene, we examined its potential role in the motile phenotype of HCC cells by both ectopic expression and knockdown investigations. RNA-interference knockdown of PFTK1 in invasive Hep3B cells resulted in a significant reduction in cell invasion, chemotactic migration, and cell motility (P < 0.001). Conversely, ectopic expression of PFTK1 in noninvasive HKCI-C3 cells induced substantial cellular invasion and migration (P < or = 0.007). In neither cell line was there any effect on cell viability. Immunofluorescence showed marked filamentous actin polymerizations in PFTK1-expressing cells.

CONCLUSION

In this study, we have thus provided preliminary evidence that overexpression of PFTK1 may confer a motile phenotype in malignant hepatocytes that accounts for the association of upregulation of this gene in metastatic HCC.

Functional characterization of human PFTK1 as a cyclin-dependent kinase

Cyclin-dependent kinases (CDKs) are crucial regulators of the eukaryotic cell cycle whose activities are controlled by associated cyclins. PFTK1 shares limited homology to CDKs, but its ability to associate with any cyclins and its biological functions remain largely unknown. Here, we report the functional characterization of human PFTK1 as a CDK. PFTK1 specifically interacted with cyclin D3 (CCND3) and formed a ternary complex with the cell cycle inhibitor p21(Cip1) in mammalian cells. We demonstrated that the kinase activity of PFTK1 depended on CCND3 and was negatively regulated by p21(Cip1). Moreover, we identified the tumor suppressor Rb as a potential downstream substrate for the PFTK1/CCND3 complex. Importantly, knocking down PFTK1 expression by using siRNA caused cell cycle arrest at G(1), whereas ectopic expression of PFTK1 promoted cell proliferation. Taken together, our data strongly suggest that PFTK1 acts as a CDK that regulates cell cycle progression and cell proliferation.

A Cdc2-related protein kinase hPFTAIRE1 from human brain interacting with 14-3-3 proteins

hPFTAIRE1 (PFTK1), a Cdc2-related protein kinase, is highly expressed in human brain. It exhibits cytoplasmic distribution in Hela cells, although it contains two nuclear localization signals (NLSs) in its N-terminus. To search for its substrates and regulatory components, we screened a two-hybrid library by using the full-length hPFTAIRE1 as a bait. Four 14-3-3 isoforms (beta, epsilon, eta, tau) were identified interacting with the hPFTAIRE1. We found a putative 14-3-3 binding consensus motif (RHSSPSS) in the hPFTAIRE1, which overlapped with its second NLS. Deletion of the RHSSPSS motif or substitution of Ser119 with Ala in the conserved binding motif abolished the specific interaction between the hPFTAIRE1 and the 14-3-3 proteins. The mutant S120A hPFTAIRE1 also showed a weak interaction to the 14-3-3 proteins. The results suggested that the Ser119 is crucial for the interaction between hPFTAIRE1 and the 14-3-3 proteins. All the hPFTAIRE1 mutants distributed in cytoplasm of Hela cells and human neuroblastoma cells (SH-SY5Y) when fused to the C-terminus of a green fluorescent protein (GFP), indicating that binding with the 14-3-3 proteins does not contribute to the subcellular localization of the hPFTAIRE1, although the binding may be involved in its signaling regulation.

Analysis of the interaction between hPFTAIRE1 and PLZF in a yeast two-hybrid system

hPFTAIRE1 is a Cdc2-related kinase family member. To search its substrates and regulatory proteins, hPFTAIRE1 was fused to LexA and used as a bait to screen a human brain LexA two-hybrid library. In this screening, seven hPFTAIRE1 interacting proteins, including promyelocytic leukemia zinc finger (PLZF), were obtained. The interaction between PLZF and hPFTAIRE1 was confirmed by beta-galactosidase assay and Leu growth activity. PLZF encodes a transcription factor belonging to the POZ/BTB domain and Krüpel zinc finger (POK) family. The highly conserved POZ/BTB domain plays a critical role in protein-protein interaction. We deleted the POZ/BTB and Krüpel zinc finger domains, respectively, and observed the interaction between hPFTAIRE1 and truncated PLZFs by liquid beta-galactosidase activity assay. A weak interaction was detected between hPFTAIRE1 and PLZF. We also observed the interaction between PLZF and another Cdc2-related kinase, PCTAIRE1. A similar result was observed. The interaction between PLZF and hPFTAIRE1 or PCTAIRE1 was confirmed by co-immunoprecipitation assay in a yeast system. PLZF is a phosphoprotein and plays multiple roles during cell growth. Our results suggest that hPFTAIRE1 and PCTAIRE1 may play important roles in the functional regulation of PLZF.

Everolimus suppresses cancellous bone loss, bone resorption, and cathepsin K expression by osteoclasts

The proliferation inhibitor of the macrolide class, everolimus, is a drug shown to be effective in the prevention of organ transplant rejection and to have a potential in the treatment of rheumatoid arthritis and certain cancers. As these diseases or their current treatments are associated with bone loss, we examined the effect of everolimus on mouse and human bone cells in vitro and on bone in an ovariectomized (OVX) rat model. Everolimus potently inhibited primary mouse and human osteoclast activity in the pit assay (IC50 values of 0.6-4.0 nM), as well as osteoclast formation, measured as the number of tartrate-resistant acid phosphatase (TRAP) multinucleated cells (IC50 values of 7.7-10.5 nM). Inhibition of osteoblastic differentiation was also observed (IC50 value of 13.5 nM). As expected, everolimus inhibited proliferation of osteoclast precursors and stimulated apoptosis, albeit with insufficient potency and efficacy to explain inhibition of osteoclast activity. Thus, everolimus appeared to directly inhibit bone resorption, which is in accord with the detected inhibition of mRNA and protein expression of cathepsin K; the main collagen-degrading protease in osteoclasts. Despite the in vitro antiproliferative activity of everolimus and the observed inhibition of osteoblast differentiation, no detrimental effects were detected at different skeletal sites in mature OVX rats at doses up to 3 mg/kg/day. This everolimus dose also prevented the OVX-induced loss of cancellous bone by 60%, an effect predominantly associated with decreased osteoclast-mediated bone resorption, resulting in a partial preservation of the cancellous bone network. Everolimus inhibited S6 kinase 1 activity in rat blood cells, skin, and bone, at doses equivalent to those used for efficacy experiments in the OVX rat model, which demonstrated in vivo targeting of the expected molecular pathway. In conclusion, everolimus directly inhibits bone resorption by osteoclasts and thus could at least be neutral or protective for bone in vivo, which would favor its use in disease indications associated with bone loss.