Growth factors are small but mighty molecules that govern the essential processes of cellular life — growth, repair, migration, and survival. When functioning properly, they ensure seamless tissue regeneration and immune balance. But when dysregulated, they drive cancer, fibrosis, and congenital anomalies. For exam prep and clinical reasoning, understanding these pathways is non-negotiable.

1. What Are Growth Factors?
   1. Key Growth Factors and Functions
2. Growth Factor Receptors: The Cellular Switchboards
   1. Receptor Types & Pathways
3. Pathological Relevance
4. Signal Flow Snapshot
5. Key takeaways:
6. Take up our quiz!
7. FAQs: Growth Factors & Receptors in General Pathology

What Are Growth Factors?

Growth factors are secreted peptides or proteins that bind to cell surface receptors and activate intracellular signaling cascades. Their primary actions include:

• Stimulating cell division and proliferation
• Enhancing wound healing and angiogenesis
• Promoting cell differentiation
• Preventing apoptosis (programmed cell death)

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Key Growth Factors and Functions

Growth Factor	Source	Primary Functions
EGF	Macrophages, salivary glands	Epithelial proliferation and repair
TGF-α	Macrophages, keratinocytes	Hepatocyte and epithelial growth
HGF	Fibroblasts	Hepatocyte proliferation, motility
VEGF	Mesenchymal cells	Angiogenesis, vascular permeability
PDGF	Platelets, macrophages	Chemotaxis, ECM protein synthesis
FGFs (FGF-1, FGF-2)	Macrophages, mast cells	Angiogenesis, fibroblast growth
TGF-β	Platelets, T cells	Fibrosis, immune suppression
KGF (FGF-7)	Fibroblasts	Keratinocyte migration/differentiation

Growth Factor Receptors: The Cellular Switchboards

Growth factors bind transmembrane receptors, which typically contain intrinsic or associated tyrosine kinase activity. Upon ligand binding, they undergo dimerization and autophosphorylation, triggering downstream signaling.

Receptor Types & Pathways

Receptor Type	Function
RTKs (e.g., EGFR, FGFR)	Trigger MAPK and PI3K/AKT pathways for growth and survival
Non-Receptor Kinases (e.g., Src)	Mediate adhesion, transcription, immune signaling
GPCRs	Activate G-proteins → cAMP/IP3 → calcium mobilization
Nuclear Receptors	Bind lipid-soluble ligands → direct gene regulation
Notch	Ligand-induced cleavage → nuclear signaling
Wnt/Frizzled	β-catenin stabilization → transcription activation

Pathological Relevance

1. Cancer: EGFR mutations → lung & colorectal cancer; VEGF → tumor angiogenesis
2. Fibrosis: TGF-β overexpression → cirrhosis, IPF, systemic sclerosis
3. Developmental Disorders: FGFR3 mutations → achondroplasia
4. Therapeutic Targets: Bevacizumab (anti-VEGF), Osimertinib (EGFR T790M), Erdafitinib (FGFR2/3)

Signal Flow Snapshot

• Ligand binding → Receptor dimerization → Tyrosine autophosphorylation
• Downstream cascades:
  
  • MAPK/ERK → Cell proliferation
  • PI3K/AKT → Cell survival
  • JAK/STAT → Differentiation and immune modulation

Key takeaways:

Growth factors and their receptors aren’t just molecular trivia — they form the backbone of how cells communicate, adapt, and survive. In disease, these pathways become therapeutic targets. In exams, they’re high-yield. In real life, they’re clinical gold.

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FAQs: Growth Factors & Receptors in General Pathology

Q1: What are growth factors in pathology?
A: Growth factors are signaling proteins that regulate cell growth, differentiation, survival, and healing, especially after tissue injury.

Q2: What is the role of VEGF in cancer?
A: VEGF (Vascular Endothelial Growth Factor) promotes angiogenesis, helping tumors form new blood vessels to support their growth.

Q3: Which mutation causes achondroplasia?
A: Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene, which inhibits cartilage proliferation.

Q4: How do receptor tyrosine kinases (RTKs) work?
A: RTKs are activated by ligand-induced dimerization and autophosphorylation, triggering signaling pathways like MAPK and PI3K/AKT.

Q5: What is the function of TGF-β in fibrosis?
A: TGF-β stimulates fibroblasts to produce collagen and extracellular matrix proteins, leading to tissue fibrosis.

Q6: What drugs target EGFR in colorectal cancer?
A: Cetuximab is a monoclonal antibody that inhibits EGFR, commonly used in EGFR-positive colorectal cancer treatment.

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