Cell Cycle Proteins

Pathogen recognition by the plant immune system is governed by structurally related, polymorphic products of disease resistance (R) genes. RAR1 and/or SGT1b mediate the function of many R proteins. RAR1 controls preactivation R protein accumulation by an unknown mechanism. We demonstrate that Arabidopsis SGT1b has two distinct, genetically separable functions in the plant immune system: SGT1b antagonizes RAR1 to negatively regulate R protein accumulation before infection, and SGT1b has a RAR1-independent function that regulates programmed cell death during infection. The balanced activities of RAR1 and SGT1, in concert with cytosolic HSP90, modulate preactivation R protein accumulation and signaling competence.

Axon degeneration is an early event in many neurodegenerative disorders. In some, the mechanism is related to injury-induced Wallerian degeneration, a proactive death program that can be strongly delayed by the neuroprotective slow Wallerian degeneration protein (Wld(S)) protein. Thus, it is important to understand the Wallerian degeneration mechanism and how Wld(S) blocks it. Wld(S) location is influenced by binding to valosin-containing protein (VCP), an essential protein for many cellular processes including membrane fusion and endoplasmic reticulum-associated degradation. In mice, the N-terminal 16 amino acids (N16), which mediate VCP binding, are essential for Wld(S) to protect axons, a role which another VCP binding sequence can substitute. In Drosophila, the Wld(S) phenotype is weakened by a similar N-terminal truncation and by knocking down the VCP homologue ter94. Neither null nor floxed VCP mice are viable so it is difficult to confirm the requirement for VCP binding in mammals in vivo. However, the hypothesis can be tested further by introducing a Wld(S) missense mutation, altering its affinity for VCP but minimizing the risk of disturbing other aspects of its structure or function. We introduced the R10A mutation, which weakens VCP binding in vitro, and expressed it in transgenic mice. R10AWld(S) fails to co-immunoprecipitate VCP from mouse brain, and only occasionally and faintly accumulates in nuclear foci for which VCP binding is necessary but not sufficient. Surprisingly however, axon protection remains robust and indistinguishable from that in spontaneous Wld(S) mice. We suggest that either N16 has an additional, VCP-independent function in mammals, or that the phenotype requires only weak VCP binding which may be driven forwards in vivo by the high VCP concentration.

UV irradiation has been reported to induce p21(WAF1/CIP1) protein degradation through a ubiquitin-proteasome pathway, but the underlying biochemical mechanism remains to be elucidated. Here, we show that ser-114 phosphorylation of p21 protein by glycogen synthase kinase 3beta (GSK-3beta) is required for its degradation in response to UV irradiation and that GSK-3beta activation is a downstream event in the ATR signaling pathway triggered by UV. UV transiently increased GSK-3beta activity, and this increase could be blocked by caffeine or by ATR small interfering RNA, indicating ATR-dependent activation of GSK-3beta. ser-114, located within the putative GSK-3beta target sequence, was phosphorylated by GSK-3beta upon UV exposure. The nonphosphorylatable S114A mutant of p21 was protected from UV-induced destabilization. Degradation of p21 protein by UV irradiation was independent of p53 status and prevented by proteasome inhibitors. In contrast to the previous report, the proteasomal d...

Summary Primary cilia, which emanate from the cell surface, exhibit assembly and disassembly dynamics along the progression of cell cycle. However, the mechanism that links ciliary dynamics and cell cycle regulation remains elusive. Here, we report that Polo-like kinase 1 (Plk1), one of the key cell cycle regulators, which regulate centrosome maturation, bipolar spindle assembly and cytokinesis, acts as a pivotal player that connects the ciliary dynamics and cell cycle regulation. We found that the kinase activity of ...

Proliferation is an important part of cancer development and progression. This is manifest by altered expression and/or activity of cell cycle related proteins. Constitutive activation of many signal transduction pathways also stimulates cell growth. Early steps in tumor development are associated with a fibrogenic response and the development of a hypoxic environment which favors the survival and proliferation of cancer stem cells. Part of the survival strategy of cancer stem cells may manifested by alterations in cell metabolism. Once tumors appear, growth and metastasis may be supported by overproduction of appropriate hormones (in hormonally dependent cancers), by promoting angiogenesis, by undergoing epithelial to mesenchymal transition, by triggering autophagy, and by taking cues from surrounding stromal cells. A number of natural compounds (e.g., curcumin, resveratrol, indole-3-carbinol, brassinin, sulforaphane, epigallocatechin-3-gallate, genistein, ellagitannins, lycopene a...

There is an urgent need to develop new drugs against eukaryotic parasitic protozoa such as Plasmodium, Trypanosoma and Leishmania, which cause the diseases malaria, trypanosomiasis and the leishmaniases respectively. The biology of these organisms has many unusual facets that might be exploited for drug design, and the recent availability of parasite genome sequence data has facilitated the search for novel drug targets. Here we review current understanding of the cell cycle in these parasites and show that important structural and functional differences exist between parasite and mammalian cell cycle control machineries and signal transduction pathways, which might be utilised for rational drug design. Potential targets include protein kinases from the cyclin-dependent kinase, cAMP-dependent kinase and mitogen activated protein kinase families.

DivIVA appears to be a mediator of inhibition by MinCD of division at the cell poles in Bacillus subtilis. Gel permeation and ultracentrifugation techniques were used to show self-association of DivIVA into a form consisting of 10-12 monomers in vitro. Western blot analysis of non-denaturating polyacrylamide gels confirms the presence of similar oligomers in B. subtilis cell lysates. These oligomers persist in a B. subtilis strain containing the divIVA1 mutation, in which proper vegetative septum positioning is abolished. In contrast, the divIVA2 mutation, which has a similar biological impact, appears to produce a protein with different oligomerization properties. The results of the present study suggest that oligomerization of DivIVA is important, but not sufficient for its function in the cell division process.

B-myb gene is expressed in neuroblastoma cells and down-regulated during differentiation. We used B-myb-transfected LAN-5 cells, which constitutively express high level of B-myb, to detect changes at phenotypic and morphological levels in basal and differentiation conditions. Our results demonstrate that the overexpression of B-myb markedly affects the cytoskeletal composition, the pattern of neurotransmitter enzymes and the extracellular matrix expression. In general, B-myb transfected neuroblastoma cells show a broad potentiality without a direction toward a specific neuroectodermal differentiation pathway. On the other hand, we confirm inhibition of the neuronal differentiation upon retinoic acid (RA) treatment of B-myb transfected cells. Furthermore, the ultrastructural analyses are supportive of a change in the metabolism in B-myb transfected cell treated with RA. Our data suggest that B-myb expression is compatible with an early phase of differentiation of neuroectodermal cells, but must be down-regulated for the completion of the differentiative programme.