TRIM16 Antibody

Basic Research Questions

• What is TRIM16 and what are its primary structural characteristics?

  TRIM16, also known as estrogen-responsive B box protein (EBBP), is a 564 amino acid member of the tripartite motif (TRIM) family. Unlike typical TRIM proteins, TRIM16 lacks a RING domain but contains two B-box-type zinc fingers, a coiled-coil region, and a B30.2/SPRY domain . Three-dimensional modeling of TRIM16 suggests that its B-box domains adopt RING-like folds, which allows TRIM16 to function as an E3 ubiquitin ligase despite the absence of a classical RING domain . The protein has a molecular mass of approximately 64 kDa, although it may appear as a 70 kDa band in some Western blot applications .

• What are the major cellular functions of TRIM16?

  TRIM16 functions as an E3 ubiquitin ligase that plays essential roles in:

  • Organizing autophagic responses to lysosomal and phagosomal damage

  • Regulating stress-induced protein aggresome biogenesis and degradation

  • Modulating the p62-KEAP1-NRF2 signaling pathway

  • Acting as a scaffold protein to facilitate autophagic degradation of protein aggregates

  • Protecting cells against oxidative stress-induced cell death

  • Regulating keratinocyte differentiation

  • Functioning as a tumor suppressor in multiple cancers

  • Inducing apoptosis through caspase-2 activation

• What is the tissue expression pattern of TRIM16?

  TRIM16 is predominantly expressed in:

  • Testis, ovary, small intestine, and colon

  • Placenta, heart, and skeletal muscle

  • Mammary gland

  Notably, TRIM16 exhibits higher expression in fetal tissues compared to their adult counterparts . In normal skin, TRIM16 is most strongly expressed in the cytoplasm and nucleus of the stratum granulosum and stratum spinosum of the epidermis, with lower expression in the stratum basale layer, indicating its expression increases as keratinocytes stop dividing and commence differentiation .

Advanced Research Applications

• How does TRIM16 regulate autophagy and protein aggregation?

  TRIM16 serves as a positive regulator of the autophagy process. Research demonstrates that TRIM16 knockout or knockdown cells show attenuated basal and MG132-induced autophagy flux compared to control cells . Conversely, overexpression of TRIM16 increases LC3B levels in HEK293T cells .

  TRIM16 facilitates autophagic degradation of protein aggregates by:

  • Acting as a scaffold protein that interacts with p62/SQSTM, ATG16L1, and LC3B/MAP1LC3B

  • Promoting the formation of aggresomes/ALIS (aggresome-like induced structures) under oxidative or proteotoxic stress conditions

  • Regulating p62, NRF2, and KEAP1 expression at both mRNA and protein levels

  Studies show that TRIM16 depletion results in smaller and fewer ubiquitin dots per cell under proteotoxic stress conditions (puromycin treatment) , indicating its essential role in the organization of protein aggregate formation and clearance.

• What role does TRIM16 play in cancer progression?

  TRIM16 functions as a tumor suppressor in multiple cancer types:

  Cancer Type	Role of TRIM16	Research Findings	Reference
  Melanoma	Inhibits migration and metastasis	TRIM16 induces IFNβ1 expression; BRAF inhibitor vemurafenib increases TRIM16 expression
  Neuroblastoma	Suppresses replication and migration	TRIM16 interacts with cytoplasmic vimentin and nuclear E2F1
  Breast cancer	Induces apoptosis	TRIM16 increases procaspase-2 protein levels
  Skin SCC	Inhibits growth and migration	TRIM16 expression decreases during progression from normal skin to SCC; TRIM16 downregulates E2F1

  TRIM16 expression is markedly reduced during the histological progression from normal skin to actinic keratosis and SCC . In melanoma tissues, high levels of TRIM16 in patients treated with vemurafenib correlated with clinical response .

• How does TRIM16 induce apoptosis in cancer cells?

  TRIM16 induces apoptosis through a novel mechanism involving caspase-2:

  • Overexpression of TRIM16 induces apoptosis in malignant cells (MCF7 breast cancer and BE(2)-C neuroblastoma cells) but not in non-malignant HEK293 cells

  • TRIM16 increases procaspase-2 protein levels in MCF7 cells at both 24 and 48 hours post-transfection

  • TRIM16 induces caspase-2 activity in both MCF7 and BE(2)-C cells

  • TRIM16 and caspase-2 proteins directly interact in MCF7 and BE(2)-C cells and co-localize in MCF7 cells

  • The induction of caspase-2 activity is required for TRIM16 to initiate apoptosis

  This mechanism represents a novel pathway by which TRIM16 can promote apoptosis in cancer cells.

• How does TRIM16 interact with other TRIM family proteins?

  TRIM16 can both homodimerize and heterodimerize with other TRIM family members:

  • TRIM16 homodimerizes through its coiled-coil domain

  • TRIM16 heterodimerizes with TRIM24, Promyelocytic leukaemia (PML) protein, and Midline-1 (MID1)

  • The interaction with MID1 suggests TRIM16 may have a function in the cytoskeleton, as MID1 associates with microtubules

  • Heterodimerization typically occurs through the coiled-coil domains

  Co-immunoprecipitation experiments confirmed that TRIM16 and MID1 form a complex in HEK293 cells . These interactions may be important for TRIM16's diverse cellular functions.

Research Applications in Cancer Studies

• How does TRIM16 function as a tumor suppressor in melanoma?

  TRIM16 functions as a tumor suppressor in melanoma through several mechanisms:

  • TRIM16 inhibits proliferation and migration of melanoma cells

  • TRIM16 induces IFNβ1 expression in melanoma cells:

    • Cancer Pathway PCR Array identified IFNβ1 as the most highly induced gene (5.2-fold) in TRIM16-transfected G361 melanoma cells

    • TRIM16 directly binds to the IFNβ1 promoter at the enhanceosome protein binding site, as demonstrated by chromatin immunoprecipitation (ChIP) assays

    • TRIM16 recruits c-Jun to the IFNβ1 promoter

  The BRAF inhibitor vemurafenib affects TRIM16 in melanoma:

  • Vemurafenib increases TRIM16 protein levels in a dose-dependent manner in melanoma cells

  • Vemurafenib markedly increases TRIM16 protein stability in melanoma cells

  • The cytopathic effects of vemurafenib partially require induction of TRIM16 expression

  • High levels of TRIM16 in melanoma tissues from patients treated with vemurafenib correlate with clinical response

• What is the relationship between TRIM16 and the p62-KEAP1-NRF2 signaling pathway?

  TRIM16 plays a critical role in regulating the p62-KEAP1-NRF2 pathway:

  • TRIM16 stabilizes NRF2 and p62 while destabilizing KEAP1, as demonstrated through cycloheximide chase experiments

  • TRIM16 regulates NRF2 and KEAP1 primarily at the protein level, while it regulates p62 at both protein and mRNA levels

  • TRIM16 directly interacts with NRF2 through its SPRY domain:

    • TRIM16 and NRF2 show strong interaction in co-immunoprecipitation assays

    • Deletion of the SPRY domain completely abolishes the interaction between TRIM16 and NRF2

    • The TRIM16 SPRY domain alone can efficiently interact with NRF2

  • TRIM16 also associates with KEAP1, and this interaction remains unchanged under proteotoxic stress conditions

  This regulatory role of TRIM16 in the p62-KEAP1-NRF2 pathway is essential for its function in stress-induced biogenesis and degradation of protein aggresomes, protecting cells against oxidative stress-induced cell death.

• How can researchers accurately measure TRIM16 protein stability in different cell types?

  To accurately measure TRIM16 protein stability:

  1. Cycloheximide Chase Assay:

     • Treat cells with cycloheximide (protein synthesis inhibitor)

     • Collect samples at different time points (0, 2, 4, 8, 12 hours)

     • Analyze TRIM16 protein levels by Western blot

     • Calculate half-life by plotting the decay curve

  Research has shown that TRIM16 half-life varies significantly between cell types:

  • TRIM16 half-life in MET-1 and MET-4 skin cancer cells: 7-7.5 hours

  • Projected TRIM16 half-life in HEK001 cells: 12 hours

  1. Proteasome Inhibition:

     • Treat cells with proteasome inhibitors (e.g., MG132)

     • Compare TRIM16 levels with and without inhibitor treatment

     • Increased levels with inhibitor suggest proteasomal degradation

  2. Ubiquitination Assay:

     • Immunoprecipitate TRIM16 under denaturing conditions

     • Probe for ubiquitin by Western blot

     • Higher molecular weight smears indicate ubiquitination

  When studying protein stability under drug treatments, note that vemurafenib markedly increases TRIM16 protein stability in melanoma cells , suggesting drug-induced post-translational modifications may affect TRIM16 stability.