Endothelial nitric-oxide synthase antisense (NOS3AS) gene encodes an autophagy-related protein (APG9-like2) highly expressed in trophoblast.
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.
Yamada
Takahiro
T
Program in Genetics and Genomic Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
Carson
Andrew R
AR
Caniggia
Isabella
I
Umebayashi
Kyohei
K
Yoshimori
Tamotsu
T
Nakabayashi
Kazuhiko
K
Scherer
Stephen W
SW
D000818:Animals; D016375:Antisense Elements (Genetics) / Q000096:biosynthesis / Q000235:genetics*; D001343:Autophagy / Q000235:genetics* / Q000502:physiology; D000071183:Autophagy-Related Proteins; D002645:Chickens; D004285:Dogs; D004331:Drosophila melanogaster; D018507:Gene Expression Regulation, Developmental; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000235:genetics*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D002679:Pan troglodytes; D051381:Rats; D012441:Saccharomyces cerevisiae; D023741:Takifugu; D014327:Trophoblasts / Q000201:enzymology*; D015027:Zebrafish
C503283:ATG9B protein, human; D016375:Antisense Elements (Genetics); C503284:Atg9b protein, mouse; D000071183:Autophagy-Related Proteins; D008565:Membrane Proteins; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; C496316:Nos3 protein, rat