Drosophila Cyclin J is a mitotically stable Cdk1 partner without essential functions

Chatterboxes: the structural and functional diversity of cyclins

Proteins of the cyclin family have divergent sequences and execute diverse roles within the cell while sharing a common fold: the cyclin box domain. Structural studies of cyclins have played a key role in our characterization and understanding of cellular processes that they control, though to date only ten of the 29 CDK-activating cyclins have been structurally characterized by X-ray crystallography or cryo-electron microscopy with or without their cognate kinases. In this review, we survey the available structures of human cyclins, highlighting their molecular features in the context of their cellular roles. We pay particular attention to how cyclin activity is regulated through fine control of degradation motif recognition and ubiquitination. Finally, we discuss the emergent roles of cyclins independent of their roles as cyclin-dependent protein kinase activators, demonstrating the cyclin box domain to be a versatile and generalized scaffolding domain for protein-protein interactions across the cellular machinery.

Rs6265 polymorphism in brain-derived neurotrophic factor (Val/Val and Val/Met) promotes proliferation of bladder cancer cells by suppressing microRNA-205 and enhancing expression of cyclin J

BACKGROUND

In this study, we evaluated the effect of rs6265 polymorphism on the expression of brain-derived neurotrophic factor (BDNF) and relevant downstream targets, as well as the involvement of this polymorphism in bladder cancer.

METHOD

A computational analysis and luciferase assays were used to explore the interaction among BDNF, miR-205, and cyclin J (CCNJ). Real-time polymerase chain reaction (RT-PCR) and Western blot analysis were carried out to determine the effect of rs6265 polymorphism on the expression of BDNF and relevant downstream genes.

RESULT

BDNF directly inhibited miR-205 expression but enhanced the expression of CCNJ, which was identified as a virtual target gene of miR-205. Furthermore, the inhibitory effect of BDNF carrying the Val genotype, defined as BDNF (Val), on miR-205 expression was much stronger than that of BDNF (Met), while the inductive effect of BDNF (Val) on CCNJ expression was much weaker than that of BDNF (Met). miR-205 and CCNJ small interfering RNA (siRNA) were found to reduce cell proliferation and arrest the cells in G0/G1 phase. In addition, miR-205 expression in patients carrying BDNF genotyped as Met/Met (defined as Met/Met group) was much higher than patients carrying BDNF genotyped as Val/Val and Val/Met (defined as Val/Val group and Val/Met group). As an inhibitor of CCNJ expression, the inhibitory effect of miR-205 was much higher in the Met/Met group than that in the Val/Val and Val/Met groups.

CONCLUSION

In summary, we suggested that the rs6265 polymorphism in BDNF upregulates the expression of CCNJ in bladder cancer via the inhibition of miR-205 expression, which leads to the promoted proliferation of bladder cancer cells.

Up-regulation of miR-146a increases the sensitivity of non-small cell lung cancer to DDP by downregulating cyclin J

Background

Cisplatin (DDP)-based chemotherapy is the common first-line therapy for lung cancer. However, their efficacy is often limited by primary drug resistance and/or acquired drug resistance. The aim of this study was to investigate the function of miRNA-146a (miR-146a) in DDP-resistant non-small cell lung cancer (NSCLC), as well as the underlying mechanisms.

Methods

The effect of overexpression of miR-146a and/or knockdown of cyclin J (CCNJ) in A549/DDP and SPC-A1/DDP cells were investigated as follows. The cellular sensitivity to DDP, cell apoptosis, cell cycle and cell mobility were detected by CCK-8, flow cytometry, hoechst staining and cell invasion/migration assay, respectively. The effects of miR-146a overexpression in NSCLC resistant cells were further analyzed in a nude mouse xenograft model.

Results

Overexpression of miR-146a and/or knockdown of CCNJ significantly increased the sensitivity to DDP in A549/DDP and SPC-A1/DDP cells compared to NC group via arresting cell cycle, enhancing cell apoptosis, inhibiting cell viability and motility in vitro and in vivo. Furthermore, miR-146a could specially degrade the mRNA of CCNJ, as examined by dual luciferase report assay.

Conclusion

The study indicates a crucial role of miR-146a in the development of acquired drug resistance to DDP in NSCLC cells. Further understanding of miR-146a mediated crosstalk networks may promote the clinical use of miR-146a analogue in NSCLC therapy.

Enterocyte Purge and Rapid Recovery Is a Resilience Reaction of the Gut Epithelium to Pore-Forming Toxin Attack

Besides digesting nutrients, the gut protects the host against invasion by pathogens. Enterocytes may be subjected to damage by both microbial and host defensive responses, causing their death. Here, we report a rapid epithelial response that alleviates infection stress and protects the enterocytes from the action of microbial virulence factors. Intestinal epithelia exposed to hemolysin, a pore-forming toxin secreted by Serratia marcescens, undergo an evolutionarily conserved process of thinning followed by the recovery of their initial thickness within a few hours. In response to hemolysin attack, Drosophila melanogaster enterocytes extrude most of their apical cytoplasm, including damaged organelles such as mitochondria, yet do not lyse. We identify two secreted peptides, the expression of which requires CyclinJ, that mediate the recovery phase in which enterocytes regain their original shape and volume. Epithelial thinning and recovery constitute a fast and efficient response to intestinal infections, with pore-forming toxins acting as alarm signals.

A role for Drosophila Cyclin J in oogenesis revealed by genetic interactions with the piRNA pathway

Cyclin J (CycJ) is a poorly characterized member of the Cyclin superfamily of cyclin-dependent kinase regulators, many of which regulate the cell cycle or transcription. Although CycJ is conserved in metazoans its cellular function has not been identified and no mutant defects have been described. In Drosophila, CycJ transcript is present primarily in ovaries and very early embryos, suggesting a role in one or both of these tissues. The CycJ gene (CycJ) lies immediately downstream of armitage (armi), a gene involved in the Piwi-associated RNA (piRNA) pathways that are required for silencing transposons in the germline and adjacent somatic cells. Mutations in armi result in oogenesis defects but a role for CycJ in oogenesis has not been defined. Here we assessed oogenesis in CycJ mutants in the presence or absence of mutations in armi or other piRNA pathway genes. CycJ null ovaries appeared normal, indicating that CycJ is not essential for oogenesis under normal conditions. In contrast, armi null ovaries produced only two egg chambers per ovariole and the eggs had severe axis specification defects, as observed previously for armi and other piRNA pathway mutants. Surprisingly, the CycJ armi double mutant failed to produce any mature eggs. The double null ovaries generally had only one egg chamber per ovariole and the egg chambers frequently contained an overabundance of differentiated germline cells. Production of these compound egg chambers could be suppressed with CycJ transgenes but not with mutations in the checkpoint gene mnk, which suppress oogenesis defects in armi mutants. The CycJ null showed similar genetic interactions with the germline and somatic piRNA pathway gene piwi, and to a lesser extent with aubergine (aub), a member of the germline-specific piRNA pathway. The strong genetic interactions between CycJ and piRNA pathway genes reveal a role for CycJ in early oogenesis. Our results suggest that CycJ is required to regulate egg chamber production or maturation when piRNA pathways are compromised.

Established and novel Cdk/cyclin complexes regulating the cell cycle and development

The identification of new members in the Cdk and cyclin families, functions for many of which are still emerging, has added new facets to the cell cycle regulatory network. With roles extending beyond the classical regulation of cell cycle progression, these new players are involved in diverse processes such as transcription, neuronal function, and ion transport. Members closely related to Cdks and cyclins such as the Speedy/RINGO proteins offer fresh insights and hope for filling in the missing gaps in our understanding of cell division. This chapter will present a broad outlook on the cell cycle and its key regulators with special emphasis on the less-studied members and their emerging roles.