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Hsc70 Regulates the Formation of Fusion‐complex Required for VTV‐Golgi Fusion
Author(s) -
Siddiqi Shadab A.,
Nafivalencia Erika,
Rahim Abdul,
Siddiqi Shaila,
Tiwari Samata,
Sabblah Thywill
Publication year - 2011
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.25.1_supplement.937.4
Subject(s) - golgi apparatus , cytosol , endoplasmic reticulum , microbiology and biotechnology , fusion protein , lipid bilayer fusion , secretory pathway , biology , snare complex , biochemistry , recombinant dna , enzyme , membrane , gene
The rate‐limiting step in the secretion of very low‐density lipoproteins (VLDL) from the liver into the plasma is their export from the endoplasmic reticulum (ER) to the Golgi, which is mediated by a specialized ER‐derived VLDL transport vesicle (VTV). VTV fuses with hepatic cis‐Golgi to facilitate the targeted delivery of VLDL to the Golgi lumen. VTV‐Golgi fusion utilizes a specific fusion‐complex composed of a unique set of SNARE proteins. Formation of fusion‐complex requires cytosol, however, cytosolic factors regulating fusion‐complex assembly remain to be identified. To identify cytosolic factors, we performed a series of chromatographic steps including FPLC on liver cytosol and recognized a protein, which we show is required for the formation of fusion‐complex. MALDI‐TOF coupled with tandam mass spectrometry analyses identified this protein as hsc70. Western blotting data using specific antibodies to hsc70 confirmed its identity. Immunodepletion of hsc70 from cytosol resulted in significant (~80%) reduction of fusion‐complex formation. Addition of recombinant hsc70 to the depleted‐cytosol completely restored the activity. Consistent with hsc70 role in fusion‐complex assembly, immunodepletion of hsc70 from hepatic cytosol significantly inhibited VTV‐Golgi fusion. We conclude that hsc70 in hepatic cytosol regulates the formation of fusion‐complex and thus VLDL‐delivery to the Golgi lumen.