Orphan kinases turn eccentric: A new class of cyclin Y-activated, membrane-targeted CDKs.
ABSTRACT 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.
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ABSTRACT: PCTAIRE1 is distant relative of the cyclin-dependent kinase family that has been implicated in spermatogenesis and neuronal development, but it has not been studied in cancer. Here we report that PCTAIRE1 is expressed in prostate, breast, and cervical cancer cells where its RNAi-mediated silencing causes growth inhibition with aberrant mitosis due to defects in centrosome dynamics. PCTAIRE1 was not similarly involved in proliferation of non-transformed cells including diploid human IMR-90 fibroblasts. Through yeast two-hybrid screening we identified tumor suppressor p27 as a PCTAIRE1 interactor. In vitro kinase assays showed PCTAIRE1 phosphorylates p27 at Ser10. PCTAIRE1 silencing modulated Ser10 phosphorylation on p27 and led to its accumulation in cancer cells but not in non-transformed cells. In a mouse xenograft model of PPC1 prostate cancer, conditional silencing of PCTAIRE1 restored p27 protein expression and suppressed tumor growth. Mechanistic studies in HeLa cells showed that PCTAIRE1 phosphorylates p27 during the S and M phases of the cell cycle. Notably, p27 silencing was sufficient to rescue cells from mitotic arrest caused by PCTAIRE1 silencing. Clinically, PCTAIRE1 was highly expressed in primary breast and prostate tumors compared to adjacent normal epithelial tissues. Together our findings reveal an unexpected role for PCTAIRE1 in regulating p27 stability, mitosis and tumor growth, suggesting PCTAIRE1 as a candidate cancer therapeutic target.Cancer Research 09/2014; · 9.28 Impact Factor
Article: Cyclin-dependent kinases.[Show abstract] [Hide abstract]
ABSTRACT: Cyclin-dependent kinases (CDKs) are protein kinases characterized by needing a separate subunit - a cyclin - that provides domains essential for enzymatic activity. CDKs play important roles in the control of cell division and modulate transcription in response to several extra- and intracellular cues. The evolutionary expansion of the CDK family in mammals led to the division of CDKs into three cell-cycle-related subfamilies (Cdk1, Cdk4 and Cdk5) and five transcriptional subfamilies (Cdk7, Cdk8, Cdk9, Cdk11 and Cdk20). Unlike the prototypical Cdc28 kinase of budding yeast, most of these CDKs bind one or a few cyclins, consistent with functional specialization during evolution. This review summarizes how, although CDKs are traditionally separated into cell-cycle or transcriptional CDKs, these activities are frequently combined in many family members. Not surprisingly, deregulation of this family of proteins is a hallmark of several diseases, including cancer, and drug-targeted inhibition of specific members has generated very encouraging results in clinical trials.Genome Biology 01/2014; 15(6):122. · 10.47 Impact Factor
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ABSTRACT: Medulloblastoma (MB) is the most common malignant brain tumor in children and is associated with a poor outcome. cMYC amplification characterizes a subgroup of MB with very poor prognosis. However, there exist so far no targeted therapies for the subgroup of MB with cMYC amplification. Here we used kinome-wide RNA interference screening to identify novel kinases that may be targeted to inhibit the proliferation of c-Myc-overexpressing MB. The RNAi screen identified a set of 5 genes that could be targeted to selectively impair the proliferation of c-Myc-overexpressing MB cell lines: AKAP12 (A-kinase anchor protein), CSNK1α1 (casein kinase 1, alpha 1), EPHA7 (EPH receptor A7) and PCTK1 (PCTAIRE protein kinase 1). When using RNAi and a pharmacological inhibitor selective for PCTK1, we could show that this kinase plays a crucial role in the proliferation of MB cell lines and the activation of the mammalian target of rapamycin (mTOR) pathway. In addition, pharmacological PCTK1 inhibition reduced the expression levels of c-Myc. Finally, targeting PCTK1 selectively impaired the tumor growth of c-Myc-overexpressing MB cells in vivo. Together our data uncover a novel and crucial role for PCTK1 in the proliferation and survival of MB characterized by cMYC amplification. INTRODUCTION Medulloblastoma (MB), a tumor arising in the cerebellum or medulla is the most prevalent malignant brain tumor in children . Current treatments including surgery, craniospinal radiotherapy and chemotherapy have improved survival rates, which nowadays are approximately 80% [2, 3]. Nevertheless, there are still numerous patients with poor prognosis and survivors suffer from diminished quality of life caused by the aggressive therapy . The current classification system for medulloblastoma is based on morphology (histopathology), and include variants such as desmoplastic/nodular, MBEN (medulloblastoma with extensive nodularity), classic medulloblastoma, large cell, and anaplastic medulloblastoma [4, 5]. During the past few years, transcriptome-based, molecular studies on cohorts of MB have depicted this tumor not as a single disease, but as a cluster of individual molecular subgroups. Four subtypes have been proposed with distinct characteristics in terms of gene expression, mutational profiles, epidemiology, and prognosis: Wnt, Shh, Group 3, and Group 4 [3, 6-8]. The most aggressive MB subtype (Group 3), that consists of 'classical' medulloblastomas and partially of the large cells/anaplastic (LCA) tumors is associated with amplification in cMyc . Current treatments fail to cure two thirds of patients in this particular group . Thus, it remains of great interest to investigate which role c-Myc plays in the biology of MB. c-Myc, a potent and frequently deregulatedOncotarget 11/2014; 1. · 6.63 Impact Factor