TIP47 (tail-interacting protein of 47 kD) was characterized as a cargo selection device for mannose 6-phosphate receptors (MPRs), directing their transport from endosomes to the trans-Golgi network. In contrast, our current analysis shows that cytosolic TIP47 is not recruited to organelles of the biosynthetic and endocytic pathways. Knockdown of TIP47 expression had no effect on MPR distribution or trafficking and did not affect lysosomal enzyme sorting. Therefore, our data argue against a function of TIP47 as a sorting device. Instead, TIP47 is recruited to lipid droplets (LDs) by an amino-terminal sequence comprising 11-mer repeats. We show that TIP47 has apolipoprotein-like properties and reorganizes liposomes into small lipid discs. Suppression of TIP47 blocked LD maturation and decreased the incorporation of triacylglycerol into LDs. We conclude that TIP47 functions in the biogenesis of LDs.

Hypoxia-inducible protein 2 (HIG2) has been implicated in canonical Wnt signaling, both as target and activator. The potential link between hypoxia and an oncogenic signaling pathway might play a pivotal role in renal clear-cell carcinoma characterized by constitutive activation of hypoxia-inducible factors (HIFs), and hence prompted us to analyze HIG2 regulation and function in detail. HIG2 was up-regulated by hypoxia and HIF inducers in all cell types and mouse organs investigated and abundantly expressed in renal clear-cell carcinomas. Promoter analyses, gel shifts, and siRNA studies revealed that HIG2 is a direct and specific target of HIF-1, but not responsive to HIF-2. Surprisingly, HIG2 was not secreted, and HIG2 overexpression neither stimulated proliferation nor activated Wnt signaling. Instead, we show that HIG2 decorates the hemimembrane of lipid droplets, whose number and size increase on hypoxic inhibition of fatty acid β-oxidation, and colocalizes with the lipid droplet proteins adipophilin and TIP47. Normoxic overexpression of HIG2 was sufficient to increase neutral lipid deposition in HeLa cells and stimulated cytokine expression. HIG2 could be detected in atherosclerotic arteries and fatty liver disease, suggesting that this ubiquitously inducible HIF-1 target gene may play an important functional role in diseases associated with pathological lipid accumulation.

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IntroductionThe proteasome, a large multicatalytic proteinase complex, is responsible for the degradation of most intracellular proteins. The proteasome has a central role in catabolism of a wide variety of proteins controlling cellular division, growth, function, and death. Numerous examples of regulatory proteins including cyclins, cyclin-dependent kinases and kinase inhibitors, oncogenes, tumor suppressor genes, and transcriptional activators and inhibitors have been found to undergo proteasomal proteolysis. Inhibition of the proteasome induces the accumulation of important regulatory intracellular proteins like cytoplasmic inhibitor of NF-B (IB␣), p53 tumor suppressor gene, and p21 and p27 cyclin-dependent kinase inhibitors, which leads to decreased NF-B activity, increased p53-mediated transcription of genes involved in apoptosis, and dysregulation of the cell cycle. [1][2][3][4] In cancer cells, the proteasome is essential to mechanisms underlying tumor cell growth, apoptosis, angiogenesis, and metastasis, thereby representing a novel target for cancer therapy. [3][4][5] Pharmacologic inhibitors of the proteasome have been shown to possess antitumor activity and have significant efficacy against a variety of malignancies. 1-2 The best characterized proteasome inhibitor, bortezomib (Velcade, previously known as PS-341; Millennium Pharmaceuticals, Cambridge, MA), is a dipeptidyl boronic acid that reversibly inhibits the chymotrypsin-like activity of the proteasome. This agent displays remarkable selectivity toward the proteasome relative to serine and cysteine proteases, and it possesses unique antitumor properties as shown in a National Cancer Institute (NCI) tumor cell line screen and in several murine xenograft models. [6][7][8][9][10][11] Bortezomib is the first proteasome inhibitor that was clinically tested in patients and became a therapeutic modality for multiple myeloma.Hodgkin lymphoma (HL) accounts for approximately 30% of all malignant lymphomas 12 with the common feature that neoplastic cells constitute only a small minority of the cells in the affected tissue, often corresponding to less than 2% of the total tumor load. Classical HL (cHL), representing approximately 95% of all HLs, is a fatal disease with 90% of untreated patients dying within 2 to 3 years. 12 The tumor cells of cHL, designated Hodgkin-ReedSternberg (H-RS) cells, are mainly derived from germinal center or post-germinal center B cells, while few (less than 2%) are derived from T cells. H-RS cells lack specific functional markers of mature B or T cells, seem to be arrested in maturation, and therefore should be physiologically prone to undergo apoptosis. [13][14] The mechanisms of apoptotic resistance in H-RS cells have been intensively investigated during the last decade. It has been shown that H-RS cells are resistant to CD95-mediated apoptosis 15 due to the constitutive expression of cFLIP. 16 In addition, H-RS cells display a defective mitochondrial apoptotic pathway 17 and uniformly show up-regulated XIAP expression, 18 whic...

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An 13 Medizinischen Fakultäten fördert die DFG Clinician Scientist‐Programme / Neue Impulse durch wissenschaftliche Qualifizierung parallel zur Facharztweiterbildung