GGR Antibody

Antigen Recognition

• Epitope: APTEK-26 peptide (residues 150–176 of GR) .

• Cross-Reactivity:

  • TRIM28: A transcriptional regulator involved in chromatin remodeling.

  • AMPD2: Adenosine monophosphate deaminase 2, an enzyme in purine metabolism .

Antibody Architecture

• Class: Mouse monoclonal IgG1 .

• Molecular Weight: Detects proteins ~100 kDa (matching TRIM28/AMPD2, not GR’s ~97 kDa) .

Validation Challenges

• GR Knockdown: Reduced 5E4 signal in HEK293 cells was initially interpreted as GR specificity but later attributed to coincidental downregulation of AMPD2 (a GR-regulated gene) .

• Immunoprecipitation-Mass Spectrometry (IP-MS):

  Target Protein	Molecular Weight (kDa)	Enrichment in IP-MS
  TRIM28	100	High
  AMPD2	100	High
  GR	97	Low
  Data from HEK293, Jurkat, and THP-1 cell lines .

Functional Implications

• Surface Staining: Clone 5E4’s signal in flow cytometry did not correlate with GR, TRIM28, or AMPD2 expression, suggesting nonspecific binding .

• Therapeutic Impact: Misidentification of GR localization or function using 5E4 could skew drug development efforts targeting GR-related pathways .

Comparative Specificity Analysis

Lessons for Antibody Validation

• Multi-Method Verification: Reliance on knockdowns alone is insufficient; orthogonal methods (e.g., IP-MS, independent antibodies) are critical .

• Batch Variability: Different 5E4 lots exhibited consistent cross-reactivity, ruling out production artifacts .

Clinical and Research Implications

• GR Signaling Studies: Clone 5E4’s cross-reactivity necessitates re-evaluation of prior findings on GR membrane localization and immune cell interactions .

• Therapeutic Antibody Development: Highlights the importance of rigorous validation for antibodies targeting GPCRs and nuclear receptors .