title: DIRAS3 regulates the autophagosome initiation complex in dormant ovarian cancer cells.
abstract: DIRAS3 is an imprinted tumor suppressor gene that is downregulated in 60% of human ovarian cancers. Re-expression of DIRAS3 at physiological levels inhibits proliferation, decreases motility, induces autophagy, and regulates tumor dormancy. Functional inhibition of autophagy with choroquine in dormant xenografts that express DIRAS3 significantly delays tumor regrowth after DIRAS3 levels are reduced, suggesting that autophagy sustains dormant ovarian cancer cells. This study documents a newly discovered role for DIRAS3 in forming the autophagosome initiation complex (AIC) that contains BECN1, PIK3C3, PIK3R4, ATG14, and DIRAS3. Participation of BECN1 in the AIC is inhibited by binding of BECN1 homodimers to BCL2. DIRAS3 binds BECN1, disrupting BECN1 homodimers and displacing BCL2. Binding of DIRAS3 to BECN1 increases the association of BECN1 with PIK3C3 and ATG14, facilitating AIC activation. Amino acid starvation of cells induces DIRAS3 expression, reduces BECN1-BCL2 interaction and promotes autophagy, whereas DIRAS3 depletion blocks amino acid starvation-induced autophagy. In primary ovarian cancers, punctate expression of DIRAS3, BECN1, and the autophagic biomarker MAP1LC3 are highly correlated (P<0.0001), underlining the clinical relevance of these mechanistic studies. Punctate expression of DIRAS3 and MAP1LC3 was detected in only 21-23% of primary ovarian cancers but in 81-84% of tumor nodules found on the peritoneal surface at second-look operations following primary chemotherapy. This reflects a 4-fold increase (P<0.0001) in autophagy between primary disease and post-treatment recurrence. We suggest that DIRAS3 not only regulates the AIC, but induces autophagy in dormant, nutrient-deprived ovarian cancer cells that remain after conventional chemotherapy, facilitating their survival.
authors.affiliation: Department of Experimental Therapeutics; The University of Texas MD Anderson Cancer Center; Houston, TX USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Lu
authors.affiliation: Department of Experimental Therapeutics; The University of Texas MD Anderson Cancer Center; Houston, TX USA.
authors.forename: Maria T
authors.initials: MT
authors.lastname: Baquero
authors.affiliation: Department of Experimental Therapeutics; The University of Texas MD Anderson Cancer Center; Houston, TX USA.
authors.forename: Hailing
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Experimental Therapeutics; The University of Texas MD Anderson Cancer Center; Houston, TX USA.
authors.forename: Maojie
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Pharmacology; Baylor College of Medicine; Houston, TX USA.
authors.forename: Albert S
authors.initials: AS
authors.lastname: Reger
authors.affiliation: Department of Pharmacology; Baylor College of Medicine; Houston, TX USA.
authors.forename: Choel
authors.initials: C
authors.lastname: Kim
authors.affiliation: Gynecologic Service; Department of Surgery; Memorial Sloan-Kettering Cancer Center; New York, NY USA.
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Levine
authors.affiliation: Department of Experimental Therapeutics; The University of Texas MD Anderson Cancer Center; Houston, TX USA.
authors.forename: Charlotte H
authors.initials: CH
authors.lastname: Clarke
authors.affiliation: Department of Experimental Therapeutics; The University of Texas MD Anderson Cancer Center; Houston, TX USA.
authors.forename: Warren S-L
authors.initials: WS
authors.lastname: Liao
authors.affiliation: Department of Experimental Therapeutics; The University of Texas MD Anderson Cancer Center; Houston, TX USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Bast
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D051017:Apoptosis Regulatory Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001343:Autophagy / Q000235:genetics / Q000502:physiology; D000071192:Autophagy-Related Protein 12; D000071183:Autophagy-Related Proteins; D000071186:Beclin-1; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008875:Middle Aged; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D010588:Phagosomes / Q000378:metabolism / Q000473:pathology; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C466624:ATG12 protein, human; C539000:ATG14 protein, human; D033942:Adaptor Proteins, Vesicular Transport; D000596:Amino Acids; D051017:Apoptosis Regulatory Proteins; D000071192:Autophagy-Related Protein 12; D000071183:Autophagy-Related Proteins; C491997:BECN1 protein, human; D000071186:Beclin-1; C117386:DIRAS3 protein, human; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D050505:Mutant Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011994:Recombinant Proteins; D025841:Small Ubiquitin-Related Modifier Proteins; D020741:rho GTP-Binding Proteins
keywords: BECN1; DIRAS3; autophagy; ovarian cancer; second-look surgery