Autophagy Driven by a Master Regulator of Hematopoiesis

Abstract

Developmental and homeostatic remodeling of cellular organelles is mediated by a complex process termed autophagy. The cohort of proteins that constitute the autophagy machinery functions in a multistep biochemical pathway. Though components of the autophagy machinery are broadly expressed, autophagy can occur in specialized cellular contexts, and mechanisms underlying cell-type-specific autophagy are poorly understood. We demonstrate that the master regulator of hematopoiesis, GATA-1, directly activates transcription of genes encoding the essential autophagy component microtubule-associated protein 1 light chain 3B (LC3B) and its homologs (MAP1LC3A, GABARAP, GABARAPL1, and GATE-16). In addition, GATA-1 directly activates genes involved in the biogenesis/function of lysosomes, which mediate autophagic protein turnover. We demonstrate that GATA-1 utilizes the forkhead protein FoxO3 to activate select autophagy genes. GATA-1-dependent LC3B induction is tightly coupled to accumulation of the active form of LC3B and autophagosomes, which mediate mitochondrial clearance as a critical step in erythropoiesis. These results illustrate a novel mechanism by which a master regulator of development establishes a genetic network to instigate cell-type-specific autophagy.C ellular differentiation requires massive remodeling of subcellular structures to accommodate specialized functions of cell progeny. For example, the differentiation of committed hematopoietic progenitors into erythrocytes requires disposal of mitochondria (mitophagy) and nuclei (enucleation), which are not required for erythrocyte function. The process whereby cells consume organelles is termed autophagy (29). Autophagy mediates morphological remodeling in developmental and pathophysiological contexts. A cohort of autophagy proteins functions in a multistep reaction to generate an autophagosome that engulfs damaged organelles (53). The subsequent fusion of the loaded autophagosome with the lysosome results in proteolysis of the engulfed proteins.Core components of the autophagy machinery are broadly expressed, and therefore diverse cell types are competent to execute autophagy. A recent proteomics analysis expanded the repertoire of proteins linked to autophagy and illustrated their complex interaction networks (2). Many questions remain unanswered regarding how this complex network of apparently ubiquitous autophagy components is established and what role cell-type-specific factors have in instigating and regulating autophagy.Since autophagy is a critical step in erythrocyte development (19,39,41,57), it is particularly instructive to analyze cell-typespecific autophagy in this context. Targeted deletion of the BCL-2 family member NIX yields anemia, impaired erythroid maturation, and impaired mitophagy during terminal erythroid differentiation (39, 41). Furthermore, a conditional knockout in hematopoietic cells of Atg7, which encodes a protein resembling a ubiquitin-activating enzyme, yields severe anemia, defective erythropoiesis, and lethality shortly af...

RCAD/Ufl1, a Ufm1 E3 ligase, is essential for hematopoietic stem cell function and murine hematopoiesis

“…This result is consistent with previous reports demonstrating that FOXO3A-and GATA-1-driven pro-autophagy gene programs function as a cytoprotective mechanism in HSCs and erythroid progenitors. 32,36 However, RCAD KO mice appear to exhibit more severe phenotype comparing to either ATG7 or FIP200 KO mice. RCAD KO embryos usually died around E11.5.…”

A large-scale analysis of autophagy-related gene expression identifies new regulators of autophagy

“…We also report that the deletion of GLN3 increases the expression of ATG8 and ATG29 in growing conditions, suggesting that the Gln3 protein is directly or indirectly involved in the repression of some ATG genes. Previous studies showed that the mammalian GATA1 and GATA4 transcription factors are involved in the expression of several autophagy-related genes, 20,23 suggesting that the function of the GATA family members in regulating autophagy is conserved from yeast to mammals.…”

“…Recent studies show that the transcriptional regulation of ATG genes is critical for autophagy: the level of Atg8, for example, correlates with autophagosome size, 16 that of Atg9 correlates with their number, 17 and the amount of Atg7 modulates autophagy amplitude. 18 In higher eukaryotes the family of FOXO transcription factors, GATA1 as well as the master regulator TFEB, activate autophagy, [19][20][21] while ZKSCAN3 and GATA4 are involved in the repression of mammalian autophagy-related genes. [22][23] In yeast, recent studies characterized Ume6 and Pho23 as transcriptional repressors of ATG genes and negative regulators of autophagy.…”

Guidelines for the use and interpretation of assays for monitoring autophagy

“…Along these lines, the erythroid transcription factor GATA1 and its coregulator Friend of GATA1 induce the transcription of multiple genes encoding autophagy components; this developmentally regulated transcriptional response is coupled to increases in autophagosome number as well as the percent of cells that contain autophagosomes. 466 Finally, CEBPB/C/EBPβ is a transcription factor that regulates autophagy in response to the circadian cycle. 467 Although less work has been done on post-transcriptional regulation, several studies implicate microRNAs in controlling the expression of proteins associated with autophagy.…”