The biogenesis of double-membrane vesicles called autophagosomes, which sequester and transport intracellular material for degradation in lysosomes or vacuoles, is a central event in autophagy. This process requires a unique set of factors called autophagy-related (Atg) proteins. The Atg proteins assemble to organize the preautophagosomal structure (PAS), at which a cup-shaped membrane, the isolation membrane (or phagophore), forms and expands to become the autophagosome. The molecular mechanism of autophagosome biogenesis remains poorly understood. Previous studies have shown that Atg2 forms a complex with the phosphatidylinositol 3-phosphate (PI3P)-binding protein Atg18 and localizes to the PAS to initiate autophagosome biogenesis; however, the molecular function of Atg2 remains unknown. In this study, we show that Atg2 has two membrane-binding domains in the N- and C-terminal regions and acts as a membrane tether during autophagosome formation in the budding yeast Saccharomyces cerevisiae. An amphipathic helix in the C-terminal region binds to membranes and facilitates Atg18 binding to PI3P to target the Atg2-Atg18 complex to the PAS. The N-terminal region of Atg2 is also involved in the membrane binding of this protein but is dispensable for the PAS targeting of the Atg2-Atg18 complex. Our data suggest that this region associates with the endoplasmic reticulum (ER) and is responsible for the formation of the isolation membrane at the PAS. Based on these results, we propose that the Atg2-Atg18 complex tethers the PAS to the ER to initiate membrane expansion during autophagosome formation.

The budding yeast kinase Hrr25 regulates two selective autophagy–related pathways by phosphorylating degradation target receptors and thereby promoting their interaction with Atg11 and the formation of autophagosomal membrane.

We examined the correlation among the levels of urinary monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8), hyperglycemia, and renal injuries in patients with type 2 diabetic nephropathy. The levels of urinary MCP-1, IL-8, protein excretion, blood urea nitrogen (BUN), serum creatinine (s-Cr), glycohemoglobin A1c (HbA1c), and fasting plasma glucose (FPG) were measured in 24 patients with type 2 diabetic nephropathy and 14 healthy adults as controls. Diabetic nephropathy was classified into three stages: stage 1 = normoalbuminuric, stage 2 = microalbuminuric, and stage 3 = macroalbuminuric. All of the patients showed normal ranges in renal function tests. Levels of urinary MCP-1 in all patients with diabetic nephropathy were significantly higher than those in healthy adults (P < 0.05). The levels of urinary MCP-1 in patients with diabetic nephropathy increased gradually according to the clinical stage of this disease. In contrast, the levels of urinary IL-8 in patients with diabetic nephropathy increased in stages 2 and 3. There was a significant correlation between the levels of urinary IL-8 and those of HbA1c. High glucose may stimulate MCP-1 and/or IL-8 production and their excretion into the urine independently of the phases or pathological lesions of this disease. It appears that IL-8 increased in the early stage of diabetic nephropathy, and MCP-1 increased in the advanced stage of this disease. It was concluded that measurement of urinary MCP-1 and IL-8 may be useful for evaluating the degree of renal injuries in patients with type 2 diabetic nephropathy.

Mitochondria play unexpected roles in sperm tail elongation in Drosophila by providing a structural platform for microtubule reorganization to support the robust elongation taking place at the tip of the very long sperm tail. The identification of mitochondria as an organizer of cytoskeletal dynamics extends our understanding of mechanisms of cell morphogenesis.

Heparin-binding EGF-like growth factor (HB-EGF) is synthesized as a type I transmembrane protein (proHB-EGF) and expressed on the cell surface. The ectodomain shedding of proHB-EGF at the extracellular region on the plasma membrane yields a soluble EGF receptor ligand and a transmembrane-cytoplasmic fragment (HB-EGF-CTF). The cytoplasmic domain of proHB-EGF (HB-EGF-cyto) interacts with transcriptional repressors to reverse their repressive activities. However, how HB-EGF-cyto accesses transcriptional repressors is yet unknown. The present study demonstrates that, after exposure to shedding stimuli, both HB-EGF-CTF and unshed proHB-EGF translocate to the nuclear envelope. Immunoelectron microscopy and digitonin-permeabilized cells showed that HB-EGF-cyto signals are at the inner nuclear membrane. A short sequence element within the HB-EGF-cyto allows a transmembrane protein to localize to the nuclear envelope. The dominant-active form of Rab5 and Rab11 suppressed nuclear envelope targeting. Collectively, these data demonstrate that membrane-anchored HB-EGF is targeted to the inner nuclear membrane via a retrograde membrane trafficking pathway.