Plays a role in autophagy. Cycles between a juxta-nuclear trans-Golgi network compartment and late endosomes. Nutrient starvation induces accumulation on autophagosomes. Starvation-dependent trafficking requires ULK1, ATG13 and FAM48A.
Autophagy, fundamentally a lysosomal degradation pathway, functions in cells during normal growth and certain pathological conditions, including starvation, to maintain homeostasis. Autophagosomes are formed through a mechanism that is not well understood, despite the identification of many genes required for autophagy. We have studied the mammalian homologue of Atg9p, a multi-spanning transmembrane protein essential in yeast for autophagy, to gain a better understanding of the function of this ubiquitious protein. We show that both the N- and C-termini of mammalian Atg9 (mAtg9) are cytosolic, and predict that mAtg9 spans the membrane six times. We find that mAtg9 is located in the trans-Golgi network and late endosomes and colocalizes with TGN46, the cation-independent mannose-6-phosphate receptor, Rab7 and Rab9. Amino acid starvation or rapamycin treatment, which upregulates autophagy, causes a redistribution of mAtg9 from the TGN to peripheral, endosomal membranes, which are positive for the autophagosomal marker GFP-LC3. siRNA-mediated depletion of the putative mammalian homologue of Atg1p, ULK1, inhibits this starvation-induced redistribution. The redistribution of mAtg9 also requires PI 3-kinase activity, and is reversed after restoration of amino acids. We speculate that starvation-induced autophagy, which requires mAtg9, may rely on an alteration of the steady-state trafficking of mAtg9, in a Atg1-dependent manner.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionIntAct
To systematically investigate innate immune signaling networks regulating production of type I interferon, we analyzed protein complexes formed after microbial recognition. Fifty-eight baits were associated with 260 interacting proteins forming a human innate immunity interactome for type I interferon (HI5) of 401 unique interactions; 21% of interactions were modulated by RNA, DNA, or LPS. Overexpression and depletion analyses identified 22 unique genes that regulated NF-κB and ISRE reporter activity, viral replication, or virus-induced interferon production. Detailed mechanistic analysis defined a role for mind bomb (MIB) E3 ligases in K63-linked ubiquitination of TBK1, a kinase that phosphorylates IRF transcription factors controlling interferon production. Mib genes selectively controlled responses to cytosolic RNA. MIB deficiency reduced antiviral activity, establishing the role of MIB proteins as positive regulators of antiviral responses. The HI5 provides a dynamic physical and regulatory network that serves as a resource for mechanistic analysis of innate immune signaling.
The formation of a double membrane-bounded structure, the autophagosome, that occurs when a specialized membrane sac, called the isolation membrane, starts to enclose a portion of the cytoplasm.
Macroautophagy is an intracellular degradation system for the majority of proteins and some organelles that is conserved in all eukaryotic species. The precise role of autophagy in mammalian development and potential involvement in disease remain to be discerned. Yeast Atg9p is the first integral membrane protein shown to be essential for the cytoplasm to vacuole targeting (Cvt) pathway and autophagy, whereas its mammalian functional orthologue has yet to be identified. We have identified two human genes homologous to yeast Atg9p and designated these as APG9L1 and APG9L2. We have previously identified APG9L2 as NOS3AS, which participates in the post-transcriptional regulation of the endothelial nitric-oxide synthase (NOS3) gene on chromosome 7 through its antisense overlap. In human adult tissues, APG9L1 was ubiquitously expressed, whereas APG9L2 was highly expressed in placenta (trophoblast cells) and pituitary gland. In transient transfection assays we found that both proteins were primarily localized to the perinuclear region and also scattered throughout the cytosol as dots, a subset of which colocalized with an autophagosome-specific marker LC3 under starvation conditions. Finally, by the small interfering RNA-mediated knockdown of APG9L1 in HeLa cells, we demonstrated that APG9L1 is essential for starvation-induced autophagosome formation. In addition, APG9L2 can functionally complement APG9L1 in this process. These results, taken together with those of phylogenetic and sequence analyses, suggest that both APG9L1 and APG9L2 are functionally orthologous to the yATG9 in autophagosome formation. Moreover, APG9L2 is a vertebrate-specific gene that may have gained critical roles in mammalian-specific developmental events, such as placentation, through rapid evolution.
Protein participating in autophagy, a process of intracellular bulk degradation in which cytoplasmic components including organelles are sequestered within double-membrane vesicles that deliver the contents to the lysosome/vacuole for degradation. There are three primary forms of autophagy: chaperone-mediated autophagy, microautophagy and macroautophagy. During macroautophagy, the sequestering vesicles, termed autophagosomes, fuse with the lysosome or vacuole resulting in the delivery of an inner vesicle (autophagic body) into the lumen of the degradative compartment.
Protein involved in the intracellular transport of proteins from one location to another. All proteins (except the ones synthesized in mitochondria and plastids) are synthesized on ribosomes in the cytosol. Most proteins remain in the cytosol. Proteins with a signal sequence either become plasma membrane components or are exported from the cell of origin.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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