Autocrine effect

Table 10.1 Overview of some polypeptide growth factors. Many can be grouped into families on the basis of amino acid sequence homology, or the cell types affected. Most growth factors are produced by more than one cell type and display endocrine, paracrine or autocrine effects on target cells by interacting with specific cell surface receptors...

Hepatocyte growth factor (HGF), also known as scatter factor, has been shown to support the survival of sympathetic neuroblasts and subpopulations of spinal motor neurons. In the former case this is apparently an autocrine effect since these cells have been shown to synthesize HGF. 

The tumour cells produce and respond to their own growth factors (an autocrine effect). 

Hormones transfer signals by migrating from their site of synthesis to their site of action. They are usually transported in the blood. In this case, they are said to have an endocrine effect (1 example insulin). By contrast, tissue hormones, the target cells for which are in the immediate vicinity of the glandular cells that produce them, are said to have a paracrine effect (2 example gastrointestinal tract hormones). When signal substances also pass effects back to the cells that synthesize them, they are said to have an autocrine effect (3 example prostaglandins). Autocrine effects are often found in tumor cells (see p. 400), which stimulate their own proliferation in this way. 

Stimulated platelets release arachidonic acid rapidly from their phospholipids, apparently as a result of activation of phospholipase A2. The released arachidonate can in turn be metabolized to endoperoxides and thromboxane A2 (Chapter 21). These compounds are also potent activators of platelets and cause a self-activating or autocrine effect.1) While PAF has a beneficial function, it can under some conditions contribute in a dangerous way to inflammation and to allergic responses including anaphylaxis,) asthmag and cold-induced urticaria.1 Although the effect of PAF is separate from those of histamine and of leukotrienes, these agents may act cooperatively to induce inflammation.1... 

Tamoxifen decreases the rate of proliferation of breast cancer cells in vitro by inhibiting the estrogen-dependent production of specific proteins and growth factors that exert autocrine effects on cell division. Antiandrogenic compounds antagonize the effects of testosterone and are of value in the treatment of hirsutism and other masculinizing syndromes. 

The mechanism by which the acrosome reaction confers fusion competence on sperm is not known. Plausible hypotheses include the following (i) activation of putative fusion peptides on sperm by acrosomal proteases or by relocalization (ii) autocrine effects on sperm of bioactive peptides released during acrosome reaction or (iii) intracellular mediators of the acrosome reaction, such as membrane depolarization or Ca (see below), express onset of fusion competence. 

Green and Nacy, 1993 Nussler and Billiar, 1993 Vane era/., 1994). Induction of iNOS can have potent toxic autocrine effects. Induction of iNOS in endothelial cells may result in endothelial damage (Estrada et al., 1992). In myocardial cells it may cause negative inotropic effects (Evans et al., 1992). It may cause apoptosis in macrophages (Albina et al., 1993) and inhibit cellular respiration in vascular smooth muscle cells (Geng et al., 1992). 

However, hormones may act on the neighboring nonhormone-producing cells. This type of interaction between the hormone-producing cells and the target tissues is termed the paracrine effect. Some hormones are released into the intercellular compartment where they act on receptors found on the same cells secreting them this action is called the autocrine effect. Hormones can also act within the cell without being released, an effect known as intracrine effect (Figure 7.2). 

Cytokines produce their effects in three ways. The first type of effect is the autocrine effect in which the cytokine acts on the same cell that produced it. An example is when IL-2 produced by activated T cells promotes T-ceU growth. The second way is when a cytokine affects other cells in its vicinity. This... 

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