Autocrine Signaling: Definition, Mechanisms, and Physiological Roles

Autocrine signaling occurs when a cell secretes a signaling molecule (hormone, cytokine, growth factor) that binds to receptors on the same cell, triggering a response. It is a fundamental mode of cellular self-regulation.

Contrast with Other Signaling Modes

Mode	Source → Target	Distance
Autocrine	Cell → Same cell	Intracellular / immediate vicinity
Paracrine	Cell → Nearby cells	Local diffusion
Endocrine	Gland → Bloodstream → Distant cells	Systemic
Juxtacrine	Cell → Adjacent cell (contact-dependent)	Direct contact

Key Examples & Functions

• Epidermal Growth Factor (EGF): Keratinocytes, fibroblasts secrete EGF → bind EGFR on same cell → proliferation, wound healing.
• TGF-β (Transforming Growth Factor-beta): Immune cells, fibroblasts, tumor cells → autocrine loop regulates differentiation, fibrosis, immune suppression, cancer progression.
• Interleukin-2 (IL-2): Activated T cells produce IL-2 → express high-affinity IL-2R (CD25) → autocrine proliferation (clonal expansion).
• Interferons (IFN-α/β): Virus-infected cells → autocrine/paracrine → antiviral state (PKR, OAS pathways).
• VEGF (Vascular Endothelial Growth Factor): Tumor cells → autocrine survival/angiogenesis.
• Prostaglandins: Local autocrine/paracrine mediators of inflammation, platelet aggregation.

Pathological Relevance

• Cancer: Autocrine loops drive uncontrolled growth, survival, metastasis (e.g., TGF-β, IGF, EGFR ligands).
• Fibrosis: Persistent TGF-β autocrine signaling in myofibroblasts.
• Autoimmunity: Autocrine cytokine production sustains activated lymphocytes.

Therapeutic Targeting

Monoclonal antibodies, receptor tyrosine kinase inhibitors, ligand traps (e.g., aflibercept for VEGF) disrupt pathogenic autocrine loops.