SFN

SFN (stratifin/14-3-3σ) is a scaffold protein that regulates cytoskeletal dynamics, cell survival, and extracellular matrix remodeling, and behaves as a context-dependent driver of proliferation and fibrosis (PMID:37946061, PMID:31144406). In cancer cells it promotes proliferation, migration, invasion, and metastasis while suppressing apoptosis by activating the LIMK2/Cofilin axis to drive actin cytoskeletal remodeling, with SFN overexpression raising LIMK2, p-LIMK2, Cofilin, and p-Cofilin levels and silencing reversing these effects (PMID:37946061). Transgenic SFN overexpression in mouse lung acts as a potent oncogene that drives lung adenocarcinoma and activates PI3K/AKT signaling (PMID:31144406). SFN exerts its effects through direct physical partners: it binds non-muscle myosin heavy chain 9 (MYH9) in the cytoplasm of renal tubular epithelial cells to promote TGF-β1- and UUO-induced renal fibrosis, increasing Col-1 and α-SMA, while SFN knockdown reduces MYH9 and alleviates fibrosis (PMID:38986830), and it forms a complex with SPARC in keratinocyte-conditioned media that induces MMP-1 (collagenase) activity and suppresses type I collagen synthesis in dermal fibroblasts, identifying SFN as a keratinocyte-derived anti-fibrogenic factor (PMID:22422640). SFN protein levels are constrained post-transcriptionally by miR-675-5p, which directly targets its 3'-UTR to repress expression and thereby modulate tumor cell invasiveness (PMID:31677258).

1. 2012 Medium

   Established that SFN acts as a secreted intercellular signal by physically partnering with SPARC to control matrix homeostasis, answering how keratinocyte-derived SFN influences fibroblast collagen turnover.

   Evidence Reciprocal Co-IP, mass spectrometry, and conditioned-media experiments with 3D protein modeling in keratinocyte/fibroblast systems

   PMID:22422640

   Open questions at the time

   • Binding interface and stoichiometry of the SFN–SPARC complex not structurally resolved
   • Mechanism linking the complex to MMP-1 induction and collagen suppression not defined
   • Single-lab finding without independent replication
2. 2019 Medium

   Identified miR-675-5p as a direct upstream repressor of SFN, showing SFN protein levels are set post-transcriptionally and influence tumor cell invasion.

   Evidence Dual-luciferase 3'-UTR reporter assay with miRNA mimic/inhibitor transfection and transwell/scratch assays in NPC cells

   PMID:31677258

   Open questions at the time

   • Downstream effectors linking SFN levels to invasion not mapped
   • Whether other miRNAs converge on the SFN 3'-UTR unknown
3. 2019 Low

   Defined SFN as a pro-survival, pro-metastatic factor in cervical cancer cells through loss-of-function phenotyping.

   Evidence siRNA silencing with proliferation, apoptosis, migration, and invasion assays in cervical cancer cells

   PMID:31779593

   Open questions at the time

   • Phenotype not yet anchored to a defined molecular pathway in this study
   • No rescue experiment to confirm specificity
4. 2019 Medium

   Demonstrated in vivo that SFN is sufficient to drive tumorigenesis, establishing it as an oncogene rather than a correlative marker.

   Evidence SFN-transgenic (Tg-SPC-SFN) mouse model with NNK carcinogen treatment, whole-exome sequencing, histopathology, and pathway analysis

   PMID:31144406

   Open questions at the time

   • Direct molecular link between SFN and PI3K/AKT activation not mechanistically dissected
   • Single-lab transgenic model
5. 2023 Medium

   Placed SFN's cancer-promoting activity onto a defined signaling axis, showing it drives cytoskeletal remodeling and metastasis via LIMK2/Cofilin.

   Evidence Gain- and loss-of-function cellular models with transwell/scratch assays, Western blot, and actin imaging in cervical cancer cells

   PMID:37946061

   Open questions at the time

   • Whether SFN binds LIMK2 directly or acts upstream indirectly not resolved
   • In vivo validation of the LIMK2/Cofilin axis absent
6. 2024 Medium

   Identified MYH9 as a direct cytoplasmic binding partner that mediates SFN-driven renal fibrosis, providing a physical mechanism for SFN's pro-fibrotic role.

   Evidence LC-MS/MS, reciprocal Co-IP, immunofluorescence co-localization, siRNA knockdown, and mouse UUO model

   PMID:38986830

   Open questions at the time

   • How SFN binding stabilizes or regulates MYH9 expression not defined
   • Connection between SFN–MYH9 and TGF-β1 signaling upstream/downstream unclear
7. 2024 Low

   Linked SFN to mitochondrial and metabolic regulation in esophageal adenocarcinoma, broadening its functional scope beyond cytoskeletal and matrix roles.

   Evidence siRNA knockdown with ROS, mitochondrial mass, membrane potential, and metabolic assays in Barrett's esophagus/EAC cells

   PMID:30404157

   Open questions at the time

   • No molecular partner or pathway identified for the mitochondrial phenotype
   • Single method category without mechanistic placement
   • Not independently confirmed

• It remains unresolved how SFN's distinct partner interactions (SPARC, MYH9) and signaling outputs (LIMK2/Cofilin, PI3K/AKT) are integrated, and whether a unifying 14-3-3 scaffolding mechanism underlies its tissue-specific roles.
• No structural model of SFN bound to its partners
• Tissue-specificity determinants of SFN function unknown
• Direct versus indirect basis of pathway activation unresolved