Recruitment of TIP47 to lipid droplets is controlled by the putative hydrophobic cleft

Ohsaki, Yuki; Mutoh, T.; Maeda, Morihiro; Tauchi-Sato, Kumi; Fujimoto, Toyoshi

doi:10.1016/j.bbrc.2006.06.074

Cited by 53 publications

(63 citation statements)

References 31 publications

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“…The amount of ADRP could be upregulated by proteasomal inhibition (Xu et al, 2005), but this did not occur in Huh7 cells under the present experimental conditions (data not shown). The suppressive effects upon the ApoB-crescent were more evident upon introduction of ADRP than of TIP47, probably because only a small fraction of TIP47 is localized to LDs under normal conditions (Ohsaki et al, 2006b). Consistent with the results of the overexpression experiments, downregulation of either ADRP or TIP47 using siRNA significantly increased the frequency of ApoB-crescents (Fig.…”

Section: Adrp and Tip47 Suppress Apob-crescent Formationsupporting

confidence: 79%

“…Our previous results have suggested that ApoB in the ApoBcrescent is destined for proteasomal and autophagic degradation (Ohsaki et al, 2006b). Combined with our present results, the ApoBcrescent is likely to be related to the degradation mechanism that copes with lipidated ApoB (Liao et al, 1998;Fisher et al, 2001;Olofsson and Boren, 2005).…”

Section: Journal Of Cell Science 121 (14)supporting

confidence: 71%

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Lipid droplets are arrested in the ER membrane by tight binding of lipidated apolipoprotein B-100

Ohsaki

Cheng

Suzuki

et al. 2008

Journal of Cell Science

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142

132

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Apolipoprotein B-100 (ApoB) is a major component of very-low-density lipoproteins, and is deposited in a region around lipid droplets (LDs) called the `ApoB-crescent'. The ApoB-crescent is thought to be related to ApoB degradation because it drastically increases when proteasome or autophagy is inhibited. In the present study, we found that ApoB-crescents were significantly reduced when ApoB lipidation was suppressed by either the inhibition or knockdown of the microsomal triglyceride-transfer protein. By contrast, ApoB-crescents increased under conditions that are presumed to cause lipidated ApoB abnormalities in secretory compartments. By electron microscopic analyses, we identified the ApoB-crescent as a thin cholesterol-rich ER cistern fused to an LD, and – topologically – this structure is equivalent to a lipid-ester globule between the two leaflets of the ER membrane. ApoB localized in the thin cisternal lumen, and its binding to LDs was resistant to alkaline treatment. Overexpression of ADRP or TIP47 suppressed the increase in the number of ApoB-crescents, whereas knockdown of these proteins had the opposite effect. From these results, we inferred that the ApoB-crescent is formed by an LD that is arrested in the ER membrane by tight binding of lipidated ApoB to its luminal surface. We suggest that ApoB processing and LD formation are closely linked.

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Section: Adrp and Tip47 Suppress Apob-crescent Formationsupporting

confidence: 79%

Section: Journal Of Cell Science 121 (14)supporting

confidence: 71%

Lipid droplets are arrested in the ER membrane by tight binding of lipidated apolipoprotein B-100

Ohsaki

Cheng

Suzuki

et al. 2008

Journal of Cell Science

Self Cite

142

132

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“…Thus, significant variation in the amino acid sequence of adipophilin may alter the structure to prevent closure of the four helix bundle and the dissociation of adipophilin from the surfaces of lipid droplets to fold into a stable soluble protein. Interestingly, published deletion mutagenesis studies for TIP47 (40) and adipophilin (41)(42)(43) reveal that sequences predicted to form these four helices are insufficient to direct the targeting of either nascent protein to lipid droplets. However, a natural splice variant of TIP47 mRNA produces a truncated form of the protein in human steroidogenic cells that includes the four helix bundle sequence but lacks the majority of N-terminal amino acids (44); this alternative form of TIP47 reportedly associates with lipid droplets (31).…”

Section: The Perilipin Family Of Structural Lipid Droplet Proteins: Lmentioning

confidence: 99%

“…However, targeting sequences have not yet been identified for S3-12, and the conformation of the protein at the lipid droplet surface is unknown. It is interesting, however, that deletion of part or all of the 11-mer repeat sequences reduced the targeting of nascent OXPAT/MLDP (46) but not TIP47 (40) or perilipin (54) to lipid droplets. Similar experiments provide ambiguous results for adipophilin; mutation of putative 11-mer repeat sequences reduced adipophilin targeting to lipid droplets in some studies (41,42) but not in others (43).…”

Section: The Perilipin Family Of Structural Lipid Droplet Proteins: Lmentioning

confidence: 99%

Thematic review series: Adipocyte Biology. The perilipin family of structural lipid droplet proteins: stabilization of lipid droplets and control of lipolysis

Brasaemle

2007

Journal of Lipid Research

884

784

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The majority of eukaryotic cells synthesize neutral lipids and package them into cytosolic lipid droplets. In vertebrates, triacylglycerol-rich lipid droplets of adipocytes provide a major energy storage depot for the body, whereas cholesteryl ester-rich droplets of many other cells provide building materials for local membrane synthesis and repair. These lipid droplets are coated with one or more of five members of the perilipin family of proteins: adipophilin, TIP47, OXPAT/MLDP, S3-12, and perilipin. Members of this family share varying levels of sequence similarity, lipid droplet association, and functions in stabilizing lipid droplets. The most highly studied member of the family, perilipin, is the most abundant protein on the surfaces of adipocyte lipid droplets, and the major substrate for cAMP-dependent protein kinase [protein kinase A (PKA)] in lipolytically stimulated adipocytes. Perilipin serves important functions in the regulation of basal and hormonally stimulated lipolysis. Under basal conditions, perilipin restricts the access of cytosolic lipases to lipid droplets and thus promotes triacylglycerol storage. In times of energy deficit, perilipin is phosphorylated by PKA and facilitates maximal lipolysis by hormonesensitive lipase and adipose triglyceride lipase. A model is discussed whereby perilipin serves as a dynamic scaffold to coordinate the access of enzymes to the lipid droplet in a manner that is responsive to the metabolic status of the adi- The ability to synthesize sterol esters or triacylglycerols and store these neutral lipids in cytoplasmic lipid droplets is a universal property of eukaryotes from yeast to humans. Although the presence of lipid droplets in cells and tissues had been noted in early observations of stained histological sections, the elucidation of the functions and composition of lipid droplets is a relatively recent development. Early hypotheses that lipid droplets provide a homeostatic mechanism to regulate intracellular lipid levels date back to studies in the 1970s in the laboratory of Michael S. Brown and Joseph L. Goldstein showing the esterification of cholesterol derived from the receptor-mediated uptake of low density lipoproteins and the depletion of cholesteryl ester stores after the withdrawal of lipoproteins from the culture medium of cells (1-3). Despite early speculation that cytosolic lipid droplets provide an important source of cholesterol for the maintenance, repair, and synthesis of membranes, very few studies throughout the 1970s and 1980s addressed the formation or dissolution of lipid droplets.The first hint that proteins coat the cytosolic surfaces of intracellular lipid droplets and play critical roles in regulating neutral lipid metabolism emerged with the discovery of perilipins on adipocyte lipid droplets in the laboratory of Constantine Londos in 1991 (4). Since the identification of perilipins, four additional lipid droplet proteins with sequence similarity to perilipins have been described in vertebrates, with two additional famil...

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“…Hydrophobic sequences in Erg1p, Erg6p and Erg7p have also been implicated in targeting to yeast droplets (Mullner et al, 2004). Targeting of TIP47, a member of the PAT (perilipin, ADRP and TIP47) family of droplet-associated proteins, appears to depend on a C-terminal hydrophobic cleft (Ohsaki et al, 2006). Likewise, a hydrophobic region within perilipin (amino acids 242-260, H1; 320-342, H2; and 349-364, H3) controls targeting (Subramanian et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Identification of a novel N-terminal hydrophobic sequence that targets proteins to lipid droplets

Zehmer

Bartz

Liu

et al. 2008

Journal of Cell Science

100

104

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AAM-B is a putative methyltransferase that is a resident protein of lipid droplets. We have identified an N-terminal 28 amino acid hydrophobic sequence that is necessary and sufficient for targeting the protein to droplets. This sequence will also insert AAM-B into the endoplasmic reticulum (ER). A similar hydrophobic sequence (1-23) in the cytochrome p450 2C9 cannot substitute for 1-28 and only inserts AAM-B into the ER, which indicates that hydrophobicity and ER anchoring are not sufficient to reach the droplet. We found that a similar N-terminal hydrophobic sequence in cytochrome b5 reductase 3 and ALDI could also heterologously target proteins to droplets. Targeting is not affected by changing a conserved proline residue that potentially facilitates the formation of a hairpin loop to leucine. By contrast, targeting is blocked when AAM-B amino acids 59-64 or 65-70, situated downstream of the hydrophobic sequence, are changed to alanines. AAM-B-GFP expressed in Saccharomyces cerevisiae is also faithfully targeted to lipid bodies, indicating that the targeting mechanism is evolutionarily conserved. In conclusion, a class of hydrophobic sequences exists that when placed at the N-terminus of a protein will cause it to accumulate in droplets and in the ER. Supplementary material available online at

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Recruitment of TIP47 to lipid droplets is controlled by the putative hydrophobic cleft

Cited by 53 publications

References 31 publications

Lipid droplets are arrested in the ER membrane by tight binding of lipidated apolipoprotein B-100

Lipid droplets are arrested in the ER membrane by tight binding of lipidated apolipoprotein B-100

Thematic review series: Adipocyte Biology. The perilipin family of structural lipid droplet proteins: stabilization of lipid droplets and control of lipolysis

Identification of a novel N-terminal hydrophobic sequence that targets proteins to lipid droplets

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