The provided reference only gives examples of protein growth factors; it doesn't specify the three major classes. Therefore, it is impossible to answer the question with the given information. However, based on general knowledge, we can rephrase and complete the question to provide a useful answer.
Here's a rephrased question:
What are the major types of growth factors, and what are some examples of protein growth factors?
Growth factors are naturally occurring substances, usually proteins or steroids, capable of stimulating cellular growth, proliferation, healing, and cellular differentiation. While not definitively categorized into only three major classes in all literature, we can broadly categorize them based on their structure and mechanism of action, considering they are often proteins:
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Protein Growth Factors: These are the most well-known and diverse group.
- Examples: vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), and platelet-derived growth factor (PDGF). (As mentioned in the provided text). These factors are crucial for processes such as angiogenesis (VEGF), skin development and wound healing (EGF), and cell growth and division (PDGF). Growth factor specificity is achieved through highly specific cell surface receptors.
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Steroid Growth Factors: These are lipid-soluble hormones that bind to intracellular receptors, affecting gene transcription.
- Examples: Estrogens, androgens, and corticosteroids. These hormones play a key role in development, metabolism, inflammation, and immune function.
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Peptide Growth Factors: Some sources may distinguish a separate class of peptide growth factors.
- Examples: Insulin-like growth factors (IGFs). IGFs are involved in cell growth and development.
