dSin1 (Stress-activated MAP kinase-interacting protein 1) is an essential, conserved subunit of the TOR complex 2 (TORC2) in Drosophila melanogaster. It functions as a scaffold/adapter protein required for TORC2 complex assembly, stability, and kinase activity. The primary molecular function of dSin1 within TORC2 is to facilitate the phosphorylation of AGC family kinases, particularly Akt/PKB at its hydrophobic motif site (S505 in Drosophila), thereby enabling downstream signaling for cell growth, metabolism, and survival. dSin1 contains a CRIM domain that recruits AGC kinase substrates and a PH-like domain that mediates membrane localization via phosphoinositide binding. Loss of dSin1 reduces body and organ size primarily through decreased cell number, and this phenotype is rescued by FoxO reduction, establishing the dSin1-TORC2-Akt-FoxO growth axis. Unlike mammalian Sin1, Drosophila dSin1 does not appear to mediate stress-induced JNK activation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0031932 TORC2 complex | IBA GO_REF:0000033 | ACCEPT | Summary: dSin1 is a core structural component of the TORC2 complex in Drosophila. This is strongly supported by phylogenetic analysis (IBA) and confirmed by experimental evidence showing that Sin1 is required for TORC2 complex formation and integrity (PMID:17043309). Reason: The annotation is well-supported. Sin1/Avo1 is an evolutionarily conserved essential component of TORC2 across eukaryotes. In Drosophila, knockdown of Sin1 disrupts the interaction between Rictor and mTOR (PMID:17043309). This represents a core function of the protein. Supporting Evidence: PMID:17043309 Sin1 is an essential component of TORC2 but not of TORC1, and functions similarly to Rictor, the defining member of TORC2, in complex formation and kinase activity. |
| GO:0038203 TORC2 signaling | IBA GO_REF:0000033 | ACCEPT | Summary: dSin1 is required for TORC2-mediated signaling, particularly for Akt phosphorylation and downstream effects on growth and metabolism. This is the core biological process in which Sin1 functions. Reason: As an essential TORC2 component, dSin1 is required for TORC2 signaling output. This is directly demonstrated in Drosophila where sin1 mutants show strongly reduced Akt hydrophobic motif phosphorylation (PMID:17369395, PMID:17043309). The IBA annotation is appropriate and represents a core function. Supporting Evidence: PMID:17369395 Mutants removing critical TORC2 components, rictor and sin1, strongly reduced AKT hydrophobic motif (HM) phosphorylation and AKT activity PMID:17043309 Knockdown of Sin1decreases Akt phosphorylation in both Drosophila and mammalian cells and diminishes Akt function in vivo. |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Cytoplasmic localization is consistent with TORC2 function. The complex localizes to various membrane compartments and cytoplasm where it can access its substrates. Reason: While a more specific localization (plasma membrane) is also annotated, cytoplasm is a valid broader term. TORC2 pools exist at various membrane and cytoplasmic locations. The IBA annotation is acceptable. Supporting Evidence: GO_REF:0000033 Phylogenetic inference based on ancestral reconstruction |
| GO:0005546 phosphatidylinositol-4,5-bisphosphate binding | IBA GO_REF:0000033 | ACCEPT | Summary: dSin1 contains a PH-like domain that mediates membrane association via phosphoinositide binding. This domain is conserved across the SIN1 family and is important for TORC2 membrane recruitment and substrate access. Reason: The PH domain of Sin1 family proteins is well-characterized for phosphoinositide binding. This binding contributes to membrane localization of TORC2 and is a direct molecular function. UniProt annotates a SIN1-type PH domain (aa 395-545) in dSin1. Deep research (Sin1-deep-research-falcon.md) confirms the PH domain mediates membrane interactions. Supporting Evidence: file:DROME/Sin1/Sin1-deep-research-falcon.md PH domain: membrane/phosphoinositide binding; CRIM: acidic protrusion that recruits AGC substrates |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: TORC2 (including Sin1) localizes to the plasma membrane via PH domain-phosphoinositide interactions. This localization is important for accessing membrane-proximal substrates like Akt. Reason: Plasma membrane localization of TORC2 is well-established in mammalian studies and is consistent with the PH domain function of Sin1. This is where TORC2 phosphorylates membrane-recruited Akt. Deep research confirms mTORC2/Sin1 pools exist at plasma membrane. Supporting Evidence: file:DROME/Sin1/Sin1-deep-research-falcon.md mTORC2/Sin1 pools reported at plasma membrane, mitochondria-associated membranes, endosomes and vesicles |
| GO:0006915 apoptotic process | IEA GO_REF:0000043 | REMOVE | Summary: This annotation derives from UniProtKB keyword mapping (Apoptosis keyword). However, this represents a significant SIGNALING OVER-EXTENSION. Sin1 functions in TORC2 signaling, which activates Akt, which can phosphorylate pro-apoptotic proteins like Bad. This creates an indirect, multi-step connection to apoptosis regulation. dSin1 is NOT directly involved in apoptotic machinery - it is a TORC2 signaling component that is many steps removed from actual apoptosis. Reason: This is a classic case of pathway over-extension annotation. The chain is: Sin1 -> TORC2 assembly -> Akt phosphorylation -> Akt activation -> (many downstream targets including) -> Bad phosphorylation -> (potential) apoptosis inhibition. Sin1 does not directly participate in apoptotic processes. Its actual function is as a TORC2 subunit enabling Akt phosphorylation. The apoptosis connection is an indirect downstream consequence that could be 4-5 enzymatic steps removed. Drosophila-specific studies on dSin1 (Charette 2008 dissertation, cited in deep research) demonstrate that its primary phenotype is reduced growth via decreased cell number (Akt-FoxO axis), not altered apoptosis. Annotating Sin1 to apoptosis would be like annotating every upstream signaling component to every downstream phenotypic outcome. The TORC2 signaling annotation (GO:0038203) appropriately captures Sin1's actual biological role. |
| GO:0031932 TORC2 complex | IEA GO_REF:0000120 | ACCEPT | Summary: Redundant with IBA annotation but from automated multi-method inference. Sin1 is unquestionably a TORC2 component. Reason: Correct annotation. Duplicates are acceptable when different evidence sources independently support the same conclusion. Supporting Evidence: PMID:17043309 Sin1 is an essential component of TORC2 but not of TORC1 |
| GO:0038203 TORC2 signaling | NAS PMID:22493059 LST8 regulates cell growth via target-of-rapamycin complex 2... | ACCEPT | Summary: This publication (LST8 regulates cell growth via TORC2) discusses TORC2 signaling in Drosophila and shows that TORC2 regulates cell growth. Sin1 is referenced as a TORC2 component. Reason: While NAS is a weaker evidence code, the annotation is correct and consistent with the core function of Sin1. The publication studies TORC2 function in Drosophila using genetic approaches. Supporting Evidence: PMID:22493059 we show that TORC2 regulates cell growth cell autonomously |
| GO:0043539 protein serine/threonine kinase activator activity | IMP PMID:17369395 Re-evaluating AKT regulation: role of TOR complex 2 in tissu... | ACCEPT | Summary: Sin1 functions as part of TORC2 to enable Akt phosphorylation and activation. As a scaffold/adapter, Sin1 contributes to kinase activation by facilitating substrate recognition and phosphorylation by the TOR kinase. Reason: This annotation captures Sin1's molecular function well. Within TORC2, Sin1 acts as a substrate adapter that recognizes and binds AGC family kinases (particularly Akt) for phosphorylation by TOR. The CRIM domain of Sin1 is specifically implicated in AGC substrate recruitment. The experimental evidence from PMID:17369395 shows that sin1 mutants have reduced Akt phosphorylation and activity. Supporting Evidence: PMID:17369395 Mutants removing critical TORC2 components, rictor and sin1, strongly reduced AKT hydrophobic motif (HM) phosphorylation and AKT activity PMID:17043309 Sin1 is required for TORC2 kinase activity in vitro |
| GO:0045887 positive regulation of synaptic assembly at neuromuscular junction | IMP PMID:22319582 Diet and energy-sensing inputs affect TorC1-mediated axon mi... | KEEP AS NON CORE | Summary: In a Drosophila tuberous sclerosis model, Rheb overexpression causes synapse overgrowth at neuromuscular junctions. This overgrowth was rescued by reducing TORC2 components (sin1, rictor) but not TORC1 components, suggesting TORC2 promotes synapse growth. Reason: While this annotation has experimental support, it represents a downstream phenotypic consequence of TORC2 signaling in a specific disease model context (tuberous sclerosis) rather than a core function of Sin1. The study shows that Sin1 reduction rescues Rheb-mediated synapse overgrowth, indicating TORC2 is required for this phenotype. However, synapse assembly regulation is a secondary outcome of TORC2-Akt signaling, not a direct molecular function of Sin1. Core functions are TORC2 complex membership and signaling. Supporting Evidence: PMID:22319582 Rheb-mediated synapse overgrowth was not rescued by knockdown of TorC1 signaling, however it was rescued by loss of the TorC2 components sin1 and rictor. |
| GO:0045887 positive regulation of synaptic assembly at neuromuscular junction | IGI PMID:22319582 Diet and energy-sensing inputs affect TorC1-mediated axon mi... | KEEP AS NON CORE | Summary: Same annotation as above with genetic interaction evidence. The study shows Sin1 genetically interacts with the Rheb/TSC pathway in synapse development. Reason: Valid genetic interaction evidence but represents a context-dependent developmental phenotype rather than core function. Mark as non-core since it is downstream of the primary TORC2 signaling role. Supporting Evidence: PMID:22319582 synapse overgrowth was only suppressed by reducing the function of Tor complex 2 (TorC2) components (Rictor, Sin1) |
| GO:0031932 TORC2 complex | IGI PMID:17043309 Identification of Sin1 as an essential TORC2 component requi... | ACCEPT | Summary: Genetic interaction evidence supports Sin1 as a TORC2 component. Sin1 knockdown disrupts Rictor-mTOR interaction, demonstrating genetic/physical interaction within the complex. Reason: Strong experimental evidence. The paper demonstrates that Sin1 is required for TORC2 complex integrity through genetic and biochemical approaches. Supporting Evidence: PMID:17043309 It also disrupts the interaction between Rictor and mTOR |
| GO:0032869 cellular response to insulin stimulus | IMP PMID:17043309 Identification of Sin1 as an essential TORC2 component requi... | ACCEPT | Summary: TORC2/Sin1 is required for insulin-stimulated Akt phosphorylation. This is a well-established upstream role of TORC2 in the insulin signaling pathway. Reason: This annotation is appropriate. TORC2 is activated downstream of insulin/growth factor signaling and is required for full Akt activation in response to insulin. Sin1 is essential for this response as a TORC2 component. Supporting Evidence: PMID:17043309 Knockdown of Sin1decreases Akt phosphorylation in both Drosophila and mammalian cells and diminishes Akt function in vivo |
| GO:0032869 cellular response to insulin stimulus | IMP PMID:17369395 Re-evaluating AKT regulation: role of TOR complex 2 in tissu... | ACCEPT | Summary: Additional experimental evidence for Sin1 role in insulin response via TORC2-Akt signaling in Drosophila. Reason: Consistent with PMID:17043309. The Drosophila sin1 mutants show impaired Akt phosphorylation, which is downstream of insulin/PI3K signaling. Supporting Evidence: PMID:17369395 Mutants removing critical TORC2 components, rictor and sin1, strongly reduced AKT hydrophobic motif (HM) phosphorylation and AKT activity |
| GO:0038203 TORC2 signaling | IGI PMID:17043309 Identification of Sin1 as an essential TORC2 component requi... | ACCEPT | Summary: Genetic evidence from Sin1 knockdown demonstrates its essential role in TORC2 signaling pathway output. Reason: Core function annotation supported by strong experimental evidence showing Sin1 is required for TORC2 kinase activity. Supporting Evidence: PMID:17043309 Sin1 is required for TORC2 kinase activity in vitro |
| GO:0046628 positive regulation of insulin receptor signaling pathway | IMP PMID:17043309 Identification of Sin1 as an essential TORC2 component requi... | ACCEPT | Summary: Sin1/TORC2 positively regulates insulin signaling by enabling Akt phosphorylation, which is a key node in the insulin receptor signaling cascade. Reason: TORC2-mediated Akt phosphorylation is an integral part of the insulin receptor signaling pathway. Sin1 is required for this step. The annotation appropriately captures this regulatory role. Supporting Evidence: PMID:17043309 Knockdown of Sin1decreases Akt phosphorylation in both Drosophila and mammalian cells and diminishes Akt function in vivo |
| GO:0046628 positive regulation of insulin receptor signaling pathway | IMP PMID:17369395 Re-evaluating AKT regulation: role of TOR complex 2 in tissu... | ACCEPT | Summary: Drosophila genetic evidence confirms Sin1's role in insulin pathway regulation through TORC2-Akt signaling. Reason: Consistent evidence from Drosophila sin1 mutants showing reduced Akt activity and impaired insulin pathway signaling. Supporting Evidence: PMID:17369395 loss of TORC2 activity strongly inhibited hyperplasia caused by elevated pathway activity, as in mutants of the tumor suppressor PTEN |
| GO:0051897 positive regulation of phosphatidylinositol 3-kinase/protein kinase B signal transduction | IMP PMID:17043309 Identification of Sin1 as an essential TORC2 component requi... | ACCEPT | Summary: Sin1/TORC2 is essential for Akt/PKB phosphorylation at the hydrophobic motif, which is required for full Akt activation downstream of PI3K signaling. Reason: This is a core function of Sin1 as part of TORC2. The complex directly phosphorylates Akt at S473 (mammalian)/S505 (Drosophila), which is essential for full kinase activation. Supporting Evidence: PMID:17043309 Sin1 together with Rictor are key components of mTORC2 and play an essential role in Akt phosphorylation and signaling |
| GO:0051897 positive regulation of phosphatidylinositol 3-kinase/protein kinase B signal transduction | IMP PMID:17369395 Re-evaluating AKT regulation: role of TOR complex 2 in tissu... | ACCEPT | Summary: Drosophila sin1 mutants show strongly reduced Akt phosphorylation and activity, demonstrating Sin1's positive regulatory role in PI3K/Akt signaling. Reason: Core function annotation. The Drosophila in vivo evidence clearly shows Sin1 is required for Akt activation. Supporting Evidence: PMID:17369395 Mutants removing critical TORC2 components, rictor and sin1, strongly reduced AKT hydrophobic motif (HM) phosphorylation and AKT activity, but showed only minor growth impairment |
| GO:0034063 stress granule assembly | IMP PMID:26054799 TORC2 mediates the heat stress response in Drosophila by pro... | KEEP AS NON CORE | Summary: TORC2 (including Sin1) is required for stress granule formation under heat stress in Drosophila. Sin1 mutants are heat sensitive and fail to properly form stress granules. Reason: This is a validated Drosophila-specific phenotype showing TORC2 mediates the heat stress response through stress granule formation. However, this appears to be a downstream consequence of TORC2-Akt signaling rather than a direct molecular function of Sin1. The stress granule phenotype is mediated through Akt phosphorylation. Mark as non-core since it is a context-dependent (heat stress) phenotypic outcome rather than the primary signaling function. Supporting Evidence: PMID:26054799 Rictor and Sin1 homozygous mutants are heat sensitive |
| GO:0019901 protein kinase binding | ISS GO_REF:0000024 | MODIFY | Summary: Sin1 binds to protein kinases, particularly Akt/PKB and TOR/mTOR, as part of its scaffold function in TORC2. This is inferred from sequence similarity to characterized orthologs. Reason: While technically correct (Sin1 does bind protein kinases), this term is too vague and uninformative. A more specific term describing Sin1's adapter/scaffold function in presenting substrates to TOR kinase would be preferable. The annotation GO:0043539 (protein serine/threonine kinase activator activity) better captures the molecular function. Proposed replacements: protein serine/threonine kinase activator activity |
| GO:0048813 dendrite morphogenesis | IMP PMID:19875983 The target of rapamycin complex 2 controls dendritic tiling ... | KEEP AS NON CORE | Summary: In Drosophila class IV dendritic arborization neurons, Sin1 and other TORC2 components are required for dendritic tiling. Sin1 mutants show inappropriate overlap of dendritic fields, similar to trc mutants. TORC2 phosphorylates the NDR kinase Tricornered to regulate dendritic tiling. Reason: This is experimentally validated in Drosophila neurons but represents a tissue-specific developmental outcome of TORC2-mediated Trc phosphorylation. The study shows TORC2 is essential for Trc phosphorylation, which then controls dendritic tiling. This is a downstream phenotype of TORC2 signaling in a specific neuronal context rather than a core molecular function. The core function (TORC2 signaling, kinase activator activity) is what enables this phenotype. Supporting Evidence: PMID:19875983 Sin1, Rictor, and target of rapamycin (TOR), components of the TOR complex 2 (TORC2), are required for dendritic tiling of class IV da neurons |
Loading supporting content…
Download this section (compressed HTML)Q: Does dSin1 regulate any TORC2 substrates beyond Akt in Drosophila? In mammals, TORC2 phosphorylates multiple AGC kinases including PKC and SGK family members. The extent to which dSin1/TORC2 regulates these substrates in Drosophila has not been systematically characterized.
Q: What is the mechanism by which TORC2/Sin1 promotes stress granule assembly? PMID:26054799 shows Sin1 mutants fail to form stress granules under heat stress, but the molecular mechanism connecting TORC2-Akt signaling to stress granule formation is not fully elucidated.
Experiment: Phosphoproteomics to identify dSin1-dependent TORC2 substrates. This would systematically identify AGC kinases and other substrates regulated by dSin1-containing TORC2 in Drosophila tissues.
Experiment: Structure-function analysis of dSin1 CRIM and PH domains to determine the specific contributions of each domain to substrate recognition and membrane localization in Drosophila.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)