transcription factors
Summary
Transcription factors are proteins that bind specific DNA sequences (promoters/enhancers) to regulate gene expression by promoting or inhibiting RNA polymerase recruitment. Mutations in transcription factor genes cause numerous developmental disorders and cancers by disrupting normal gene regulation programs.
Detail
Transcription factors (TFs) contain DNA-binding domains (e.g., zinc finger, helix-turn-helix, leucine zipper, HLH) that recognize specific consensus sequences and activation/repression domains that interact with coactivators, corepressors, or the basal transcription machinery (RNA Pol II, TFIID, etc.) to modulate gene expression. They act combinatorially, integrating signals from multiple pathways to determine cell-type-specific and context-specific gene expression patterns. High-yield examples for boards: HOX genes (limb/axial patterning; mutations cause limb malformations), PAX genes (PAX6-aniridia, PAX3-Waardenburg syndrome), SOX9 (testis determination; mutations cause campomelic dysplasia/sex reversal), WT1 (Wilms tumor, Denys-Drash syndrome), p53 (tumor suppressor TF; Li-Fraumeni syndrome, most commonly mutated gene in cancer), MYC (oncogene, Burkitt lymphoma t(8;14)), GATA1 (erythroid/megakaryocyte differentiation, associated with Down syndrome-related leukemias), FOXP2 (language development), FOXP3 (Treg development; mutations cause IPEX syndrome), STAT proteins (JAK-STAT signaling, activated by cytokine receptors, dimerize and translocate to nucleus), NF-κB (inflammation, immune response), HIF-1α (hypoxia response, angiogenesis via VEGF), CREB (cAMP response element binding, memory formation), and nuclear hormone receptors (steroid/thyroid receptors that function as ligand-activated TFs). Clinically, TF mutations often cause syndromes with variable penetrance due to haploinsufficiency or dominant-negative effects, and TF dysregulation (overexpression, translocation, or loss) is a common mechanism in oncogenesis (e.g., translocations creating fusion TFs in leukemias/sarcomas like EWS-FLI1 in Ewing sarcoma, PML-RARA in APL). Understanding TF function is essential for grasping developmental biology, molecular genetics, and cancer pathogenesis on Step 1.
Sources
- First Aid for the USMLE Step 1
- Molecular Biology of the Cell (Alberts et al.)
- Robbins and Cotran Pathologic Basis of Disease
- Lippincott's Illustrated Reviews: Biochemistry
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