Sabine Westphal

VIPP1, a nuclear gene of Arabidopsis thaliana essential for thylakoid membrane formation

The conversion of light to chemical energy by the process of photosynthesis is localized to the thylakoid membrane network in plant chloroplasts. Although several pathways have been described that target proteins into and across the thylakoids, little is known about the origin of this membrane system or how the lipid backbone of the thylakoids is transported and fused with the target membrane. Thylakoid biogenesis and maintenance seem to involve the flow of membrane elements via vesicular transport. Here we show by mutational analysis that deletion of a single gene called VIPP1 (vesicle-inducing protein in plastids 1) is deleterious to thylakoid membrane formation. Although VIPP1 is a hydrophilic protein it is found in both the inner envelope and the thylakoid membranes. In VIPP1 deletion mutants vesicle formation is abolished. We propose that VIPP1 is essential for the maintenance of thylakoids by a transport pathway not previously recognized.

Vipp1 deletion mutant of Synechocystis: A connection between bacterial phage shock and thylakoid biogenesis?

Plant chloroplasts originated from an endosymbiotic event by which an ancestor of contemporary cyanobacteria was engulfed by an early eukaryotic cell and then transformed into an organelle. Oxygenic photosynthesis is the specific feature of cyanobacteria and chloroplasts, and the photosynthetic machinery resides in an internal membrane system, the thylakoids. The origin and genesis of thylakoid membranes, which are essential for oxygenic photosynthesis, are still an enigma. Vipp1 (vesicle-inducing protein in plastids 1) is a protein located in both the inner envelope and the thylakoids of Pisum sativum and Arabidopsis thaliana. In Arabidopsis disruption of the VIPP1 gene severely affects the plants ability to form properly structured thylakoids and as a consequence to carry out photosynthesis. In contrast, Vipp1 in Synechocystis appears to be located exclusively in the plasma membrane. Yet, as in higher plants, disruption of the VIPP1 gene locus leads to the complete loss of thylakoid formation. So far VIPP1 genes are found only in organisms carrying out oxygenic photosynthesis. They share sequence homology with a subunit encoded by the bacterial phage shock operon (PspA) but differ from PspA by a C-terminal extension of about 30 amino acids. In two cyanobacteria, Synechocystis and Anabaena, both a VIPP1 and a pspA gene are present, and phylogenetic analysis indicates that VIPP1 originated from a gene duplication of the latter and thereafter acquired its new function. It also appears that the C-terminal extension that discriminates VIPP1 proteins from PspA is important for its function in thylakoid formation.

Apoptosis: Targets in Pancreatic Cancer

Pancreatic adenocarcinoma is characterized by poor prognosis, because of late diagnosis and lack of response to chemo- and/or radiation therapies. Resistance to apoptosis mainly causes this insensitivity to conventional therapies. Apoptosis or programmed cell death is a central regulator of tissue homeostasis. Certain genetic disturbances of apoptotic signaling pathways have been found in carcinomas leading to tumor development and progression. In the past few years, the knowledge about the complex pathways of apoptosis has strongly increased and new therapeutic approaches based on this knowledge are being developed. This review will focus on the role of apoptotic proteins contributing to pancreatic cancer development and progression and will demonstrate possible targets to influence this deadly disease.

A vesicle transport system inside chloroplasts

Intracellular transport via membrane vesicle traffic is a well known feature of eukaryotic cells. Yet, no vesicle transport system has been described for prokaryotes or organelles of prokaryotic origin, such as chloroplasts and mitochondria. Here we show that chloroplasts possess a vesicle transport system with features similar to vesicle traffic in homotypic membrane fusion. Vesicle formation and fusion is affected by specific inhibitors, e.g. nucleotide analogues, protein phosphatase inhibitors and Ca2+ antagonists. This vesicle transfer is an ongoing process in mature chloroplasts indicating that it represents an important new pathway in the formation and maintenance of the thylakoid membranes.

PKC|[mu]| prevents CD95-mediated apoptosis and enhances proliferation in pancreatic tumour cells

Loss of growth control and a marked resistance to apoptosis are considered major mechanisms driving tumour progression. Protein kinases C (PKC) have been shown to be important in the regulation of proliferation and apoptosis. In this report, we investigated the role of the PKC-like kinase PKCμ in the control of these processes in pancreatic adenocarcinoma cells. We demonstrate that in these cells, PKCμ expression strongly correlates with resistance to CD95-induced apoptosis. Inhibition of PKCμ with Goe6983 sensitized resistant cells to CD95-induced apoptosis. In CD95-sensitive Colo357 cells, forced overexpression of PKCμ strongly reduced CD95-mediated apoptosis, an effect that could be reversed by pretreatment with Goe6983. In addition, PKCμ overexpression led to a strongly enhanced cell growth and to a significant increase of telomerase activity. In an attempt to identify the signalling pathways affected by PKCμ, we identified the antiapoptotic proteins c-FLIPL and survivin to be strongly upregulated in PKCμ overexpressing cells. Immunohistochemical analysis of pancreatic tumour tissue of 48 patients and 10 normal pancreatic tissues revealed marked overexpression of PKCμ in tumours. In conclusion, we showed that PKCμ controls proliferative, as well as anti-apoptotic, signalling pathways and therefore plays an important role in acquiring the malignant phenotype of pancreatic tumours.

Cell and chloroplast division requires ARTEMIS

Chloroplasts are endosymbiotic organelles of cyanobacterial origin. It seems reasonable to assume that cell division and organelle division still share general principles, as shown for the FtsZ proteins. However, further components involved in this process are largely unknown. Here we describe ARTEMIS, a nuclear-encoded protein of chloroplast inner envelope membranes that is required for organelle division. ARTEMIS consists of three distinct modules: an N-terminal receptor-like region, a centrally positioned glycine-rich stretch containing a nucleoside triphosphate-binding site, and a C-terminal YidC/Oxa1p/Alb3 protein translocase-like domain. Analysis of Arabidopsis En-1 transposon mutants as well as ARTEMIS antisense plants revealed chloroplasts arrested in the late stages of division. Chloroplasts showed clearly separated and distinct multiple thylakoid systems, whereas the final organelle fission remained unaccomplished. Inactivation of a cyanobacterial gene with sequence similarity to the YidC/Oxa1p/Alb3-like domain of ARTEMIS resulted in aberrant cell division, which could be rescued by the Arabidopsis protein. ARTEMIS represents a so-far-unrecognized link between prokaryotic cell fission and chloroplast division.

Humane duktale Pankreas-Adenokarzinome zeigen eine hohe Expression von Proteinkinase Cμ, einem starken Induktor von Apoptose-Resistenz und Zellproliferation

Aim of the study Recently, we have shown that CD95-resistant pancreatic adenocarcinoma cells express high levels of Protein Kinase Cμ (PKCμ). In this study we investigated the role of PKCμ in the regulation of proliferation and apoptosis. Additionally we tested the expression of PKCμ in pancreatic tumour tissues.