Proliferation or Differentiation

A variety of signals can be transmitted across membranes without the actual flow of a substance from one side of the membrane to the other. We saw in chapter 12 that some hormones bind to specific receptor sites on the outer surface of the plasma membrane, thereby triggering metabolic changes on the cytosolic side of the membrane. Hormonal systems that function in this way are discussed in greater detail in chapter 24. Other membrane proteins mediate specific cell-cell interactions. Sometimes these interactions merely stimulate particular types of cells to bind to one another, but often they also trigger reactions that result in proliferation or differentiation of the interacting cells. We discuss signals of this type when we consider the interaction between the B and T cells of the immune system (see Supplement 3). 

Somatomedin C probably mediates many of the actions of GH. The hormone also has specific effects on the proliferation or differentiation of many cells, including fibroblasts and chondrocytes. 

T, Sehested M, Lukas J, Bartek J. DNA damage-activated kinase Chk2 is independent of proliferation or differentiation yet correlates with tissue biology. Cancer Res. 2001 61 4990-4993. Ahn JY, Li X, Davis HL, Canman CE. Phosphorylation of threonine 68 promotes oUgomerization and autophosphorylation of the Chk2 protein kinase via the forkhead-associated domain. J. Biol. Chem. 2002 277 19389-19395. 

S Additional information <192> (<192>, Esk kinase may play some role in the control of cell proliferation or differentiation [363]) [363]... 

Growth factors bind to receptors on the cell surface and subsequently activate cellular proliferation or differentiation. Many growth factors stimulate cellular division in numerous cell type, whereas others are specific to particular cell types. They often promote cell differentiation and maturation, whereas varies between growth factors. For example, bone morphogenic proteins stimulate bone cell differentiation, whereas vascular endothelial growth factors stimulate blood vessel differentiation. 

Once cells are recruited to a biomaterial, they may he programmed (e.g., induced to proliferate or differentiate) using hoth local soluhle cues and adhesive interactions with... 

It is well known that proliferation or differentiation of nerve or muscle tissue can be enhanced by electrical stimulation, which is in part attributed to the propagation of action potentials upon stimulation. To exploit these physiological events, composites of biodegradable polymers with electroconduc-tive materials have been investigated for effective transmission of electrical signals to the cells cultured on them. PLCL and polyaniline, one of the widely used electrically conductive materials, were mixed to fabricate the nanofiber meshes, illustrating that myotube formation was accelerated when the myoblasts were cultured on polyaniline-containing nanofibers compared to that of PLCL-only nanofibers, even without electrical stimulation (Jun et ah, 2009). Another electroconductive polymer, polypyrrole, was also used as a composite with other synthetic polymers. For example, polypyrrole was incorporated as particles into polylactide scaffolds, and the fibroblasts cultured on them with various intensities of DC current showed controlled proliferation in a current-dependent manner (Shi et al., 2004). 

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