epidermal-growth-factor and Starvation

Autophagy requires diverse membrane sources and involves membrane trafficking of mATG9, the only membrane protein in the ATG family. However, the molecular regulation of mATG9 trafficking for autophagy initiation remains unclear. Here we identified two conserved classic adaptor protein sorting signals within the cytosolic N-terminus of mATG9, which mediate trafficking of mATG9 from the plasma membrane and trans-Golgi network (TGN) via interaction with the AP1/2 complex. Src phosphorylates mATG9 at Tyr8 to maintain its endocytic and constitutive trafficking in unstressed conditions. In response to starvation, phosphorylation of mATG9 at Tyr8 by Src and at Ser14 by ULK1 functionally cooperate to promote interactions between mATG9 and the AP1/2 complex, leading to redistribution of mATG9 from the plasma membrane and juxta-nuclear region to the peripheral pool for autophagy initiation. Our findings uncover novel mechanisms of mATG9 trafficking and suggest a coordination of basal and stress-induced autophagy.

Topics: Amino Acid Sequence; Autophagy; Autophagy-Related Protein-1 Homolog; Autophagy-Related Proteins; Cell Membrane; Conserved Sequence; Epidermal Growth Factor; HEK293 Cells; HeLa Cells; Humans; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Phosphorylation; Phosphotyrosine; Protein Transport; src-Family Kinases; Starvation; Stress, Physiological; Vesicular Transport Proteins

Epidermal growth factor (EGF) stimulates repair in the damaged intestine, but its role in the normal intestine is not clear. Because EGF receptors are found on the basolateral surface but not the luminal surface, we hypothesized that mucosal permeability regulates EGF binding. Adult male rats were divided into 3 groups, one that was fed normal chow (the control), one that was starved for 4 days, and one that was given methotrexate (MTX) intragastrically (10 mg/kg/day for 3 days). The rats were sacrificed and everted sacks of the jejunum were made and incubated in EGF solution. Western blot analysis of mucosal homogenates showed that the amount of phosphotyrosyl EGF receptor in the starved and MTX-treated groups was, respectively, about 1.5 times and 2 times that in the control group. The mucosal permeability in the starved and MTX treated groups also increased and varied directly with the amount of phosphotyrosyl EGF receptor. These results suggest that in the adult rat intestine, luminal EGF may play a role only under tissue damage, where enhanced permeability permits the EGF to pass through the mucosa and bind to its receptor on the basolateral membrane.

Topics: Animals; Epidermal Growth Factor; ErbB Receptors; Indicators and Reagents; Intestinal Mucosa; Intestine, Small; Intubation, Gastrointestinal; Male; Methotrexate; Nucleic Acid Synthesis Inhibitors; Permeability; Phenolsulfonphthalein; Phosphorylation; Rats; Rats, Wistar; Starvation; Time Factors

Topics: Animals; Calcium; Eating; Epidermal Growth Factor; Liver; Male; Mitochondria, Liver; Oxygen Consumption; Pyruvate Dehydrogenase Complex; Rats; Rats, Inbred Strains; Reference Values; Starvation

Insulin and EGF cause identical stimulation (congruent to 40%) of fatty acid synthesis in hepatocytes isolated from rats which have been starved and then refed a low-fat diet. In both cases this stimulation is associated with increased phosphorylation of ATP-citrate lyase and of a specific site on acetyl-CoA carboxylase. However, the altered phosphorylation of acetyl-CoA carboxylase is not associated with a change in kinetic parameters which is detectable in the purified enzyme. Whatever the mechanism involved, stimulation of fatty acid synthesis by growth factors may have a role in providing new phospholipid for growth of membranes.

Topics: Acetyl-CoA Carboxylase; Animals; ATP Citrate (pro-S)-Lyase; Epidermal Growth Factor; Fatty Acids; Female; Insulin; Ligases; Liver; Phosphoproteins; Phosphorylation; Pregnancy; Rats; Starvation

Epidermal growth factor (EGF) has been measured in extracts of submandibular glands from mice with hereditary muscular dystrophy. RIA results show that adult male and female dystrophic mice have significantly less submandibular gland EGF than do unafflicted controls. Despite the differences in gland content of the protein, serum levels of EGF are similar in both dystrophic and control animals. Furthermore, submandibular gland concentrations of amylase are normal in the dystrophic mice, indicating that not all proteins synthesized by the glands are affected. Gel filtration studied reveal that the elution properties of EGF in extracts of glands from dystrophic and control animals are indistinguishable. Unexpectedly, the chromatographic profiles indicate that most of the EGF in gland extracts elutes as a low molecular weight protein when the molecule is studied at low, biologically active concentrations; only a small portion of the protein is associated with a high molecular weight complex. Under the same experimental conditions, submandibular gland nerve growth factor maintains its association with other components in a high molecular weight form.

Topics: Amylases; Animals; Carrier Proteins; Chromatography, Gel; Epidermal Growth Factor; Female; Male; Mice; Molecular Weight; Muscular Dystrophy, Animal; Peptides; Sex Factors; Starvation; Submandibular Gland