Chromosomal mapping of the PFTAIRE gene, Pftk1, a cdc2-related kinase expressed predominantly in the mouse nervous system

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.

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.

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.

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.

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.