Nelfinavir induces liposarcoma apoptosis through inhibition of regulated intramembrane proteolysis of SREBP-1 and ATF6.

Abstract

PURPOSE:

We previously reported that nelfinavir (NFV) induces G(1) cell-cycle block and apoptosis selectively in liposarcoma cell lines due to increased SREBP-1 (sterol regulatory element binding protein-1) expression in the absence of increased transcription. We postulate that NFV interferes with regulated intramembrane proteolysis of SREBP-1 and ATF6 (activating transcription factor 6).

EXPERIMENTAL DESIGN:

Time-lapse, confocal microscopic studies show that NFV inhibits the nuclear translocation of full-length SREBP-1-EGFP and ATF6-EGFP fusion proteins. siRNA-mediated knockdown of site-1 protease (S1P) and/or site-2 protease (S2P) leads to inhibition of SREBP-1 intracellular trafficking to the nucleus and reduces liposarcoma cell proliferation. Treatment of LiSa-2 liposarcoma cells with 3,4-dichloroisocoumarin, a serine protease inhibitor of S1P, did not affect SREBP-1 processing. In contrast, 1,10-phenanthroline, an S2P-specific inhibitor, reproduces the molecular and biological phenotypes observed in NFV-treated cells, which implicates S2P as a target of NFV. In vivo evaluation of NFV in a murine liposarcoma xenograft model leads to inhibition of tumor growth without significant toxicity.

RESULTS:

NFV-induced upregulation of SREBP-1 and ATF6 results from inhibition of S2P, which together with S1P mediates regulated intramembrane proteolysis from their precursor to their transcriptionally active forms. The resulting endoplasmic reticulum (ER) stress and concurrent inhibition of the unfolded protein response induce caspase-mediated apoptosis.

CONCLUSIONS:

These results provide new insight into the mechanism of NFV-mediated induction of ER stress and cell death in liposarcomas and are the first to report targeting S2P for cancer therapy.

• Authors: Min Guan, Kristen Fousek, Chunling Jiang, Song Guo, Tim Synold, Bixin Xi, Chu-Chih Shih, Warren A Chow
• Journal: Clinical cancer research : an official journal of the American Association for Cancer Research (Clin Cancer Res) Vol. 17 Issue 7 Pg. 1796-806 (Apr 01 2011) ISSN: 1557-3265 [Electronic] United States
• PMID: 21355074 (Publication Type: Journal Article)

Chemical References

• ATF6 protein, human
• Activating Transcription Factor 6
• Antineoplastic Agents
• Coumarins
• Isocoumarins
• Phenanthrolines
• Protease Inhibitors
• RNA, Small Interfering
• Recombinant Fusion Proteins
• SREBF1 protein, human
• Sterol Regulatory Element Binding Protein 1
• hydroxy-t-butylamidenelfinavir
• 3,4-dichloroisocoumarin
• FASN protein, human
• Fatty Acid Synthase, Type I
• Proprotein Convertases
• Serine Endopeptidases
• membrane-bound transcription factor peptidase, site 1
• Caspase 6
• Caspase 9
• Metalloendopeptidases
• MBTPS2 protein, human
• Nelfinavir
• 1,10-phenanthroline

Topics

• Activating Transcription Factor 6 (metabolism)
• Animals
• Antineoplastic Agents (pharmacokinetics, pharmacology)
• Apoptosis (drug effects)
• Caspase 6 (metabolism)
• Caspase 9 (metabolism)
• Cell Line, Tumor
• Cell Nucleus (metabolism)
• Cell Proliferation (drug effects)
• Cell Survival (drug effects)
• Coumarins (pharmacology)
• Endoplasmic Reticulum (drug effects, physiology)
• Enzyme Activation
• Fatty Acid Synthase, Type I (genetics, metabolism)
• Female
• Humans
• Isocoumarins
• Liposarcoma (drug therapy, pathology)
• Metalloendopeptidases (antagonists & inhibitors, genetics)
• Mice
• Mice, SCID
• Nelfinavir (analogs & derivatives, pharmacokinetics, pharmacology)
• Neoplasm Transplantation
• Phenanthrolines (pharmacology)
• Proprotein Convertases (genetics, metabolism)
• Protease Inhibitors (pharmacology)
• Protein Transport
• RNA Interference
• RNA, Small Interfering (genetics)
• Recombinant Fusion Proteins (genetics, metabolism)
• Serine Endopeptidases (genetics, metabolism)
• Sterol Regulatory Element Binding Protein 1 (metabolism)
• Transcription, Genetic
• Transplantation, Heterologous
• Tumor Burden (drug effects)