Constitutive secretion

Constitutive secretion Regulated secretion Neuronal secretion... 

All eukaryotic cells possess an unspecialized exocytic pathway known as the constitutive secretion. Vesicle membranes in this pathway fuse with the plasma membrane without any extracellular signal. As noted above, proteins destined for the secretory pathway are sorted at the level of the TGN. Proteins to be transported to the plasma membrane are directed into a constitutive secretory pathway. 

B cells are named after the bursa of Fabricus, the organ located in birds from which B cells mature. B cells mature with the bone marrow in mammals. B cells can be separated into two main classes plasma cells, which constitutively secrete antibodies, and memory cells, which secrete antibodies only in response to reexposure to particular antigen (Figure 7.1b). B cells can be further classified into B1 and B2 cells. B1 cells were first... 

Lu, P., Jones, L.L., Snyder, E.Y., Tuszynski, M.H. (2003). Neural stem cells constitutively secrete neurotrophic factors and promote extensive host axonal growth after spinal cord injury. Exp Neurol, 181, 115-29. 

In our previous study we found that cultured human myoblasts, fusing myoblasts and myotubes constitutively secrete interleukin-6 (IL-6) (Prelovsek et al., 2006). This cytokine is known as the major eytokine released from the skeletal musele under various eonditions (Febbraio and Pedersen, 2005). We also found that IL-6 secretion is stimulated by the major proinflammatory agents like tumor necrosis factor (TNF)-a and endotoxin lipopolysaccharide (EPS). Sinee IL-6 is a potent stimulator of myoblast... 

On the other hand, viral proteins have been identified in exosomes secreted by dendritic cells (Table 2) and might reflect the presence of endogenous retrovimses in the cell line used (Thery et al. 1999,2001). In addition, we have expressed a chimeric protein containing the cytosolic domain of the transmembrane envelope protein of bovine leukaemia virus in K562 cells and found that the chimera was sorted into constitutively secreted exosomes (unpublished results). 

Cultured cells from enzymatically dispersed, carrageenan-induced granulomas display several characteristics of mononuclear phagocytes— namely, Fc rggeptors, phagocytic activity, and the constitutive secretion of lysozyme. 

The polymerization of insuHn and proinsulin to dimers and hexamers is a very important process which takes place in the pancreas and impacts upon the pharmaceutical application of insuHn, because the dissociation of the polymers is the rate-limiting processes in the absorption and action in the tissues of the biological active monomeric insulin [45]. The polymerization diminishes osmotic pressure and hy-drophobicity and improves solubility. A positive correlation between expression yield and the degree of polymerization was found [46] that supports yeast in vivo polymerization of insulin precursors and accentuates its importance. However, polymerization can also account for a drawback by retention of product in the vacuole [47]. Intracellular retention of a substantial quantity of the synthesized insulin precursor indicated that the insulin precursor followed two different intracellular routes in the late secretory pathway [12, 47]. Constitutive secretion to the culture supernatant may reflect saturation of a sorting mechanism in the late Golgi due to overexpression. The kexin cleaves the leader-insulin precursor peptide in a late Golgi compartment to yield free insulin precursor, and... 

As noted In the chapter Introduction, all eukaryotic cells continuously secrete certain proteins, a process commonly called constitutive secretion. Specialized secretory cells also store other proteins In vesicles and secrete them only when triggered by a specific stimulus. One example of such regulated secretion occurs In pancreatic p cells, which store newly made Insulin In special secretory vesicles and secrete Insulin In response to an elevation In blood glucose (see Figure 15-7). These and other secretory cells simultaneously utilize two different types of vesicles to move proteins from the trans-Golgi network to the cell surface regulated transport vesicles, often simply called secretory vesicles, and unregulated transport vesicles, also called constitutive secretory vesicles. 

Madinger CL, Collins K, Fields LG, Taron CH, Benner JS. Constitutive secretion in Tetrahynnena thermophila. Eukaryot Cell. 2010 9 674-81. 

A small fraction of the precursor vWf is not processed but is secreted constitutively from the cells along with the processed vWf. It appears that this constitutively secreted vWf is functionally different from vWf that is secreted from the Weibel-Palade bodies after endothelial cell stimulation. The vWf originating from the Weibel-Palade bodies is aggregated into larger multimers and binds more avidly to platelets and extracellular matrix components (269). 

Poltorak, A. N., Bazzoni, F., Smirnova, H, Alejos, E., Thompson, P., Luheshi, G., Rothwell, N., and Beutler, B. (1995) MIP-1 gamma molecular cloning, expression, and biological activities of a novel CC chemokine that is constitutively secreted in vivo. J. Inflamm. 45(3), 207-219. Youn, B. S., Jang, I. K., Broxmeyer, H. E., Cooper, S., Jenkins, N. A., Gilbert, D. J., Copeland, N. G., Elick, T. A., Fraser, M. J., Jr., and Kwon, B. S. (1995) A novel chemokine, macrophage inflammatory protein-related protein-2, inhibits colony formation of bone marrow myeloid progenitors. J. Immunol. 155(5), 2661-2667. 

Miller, S. G., and Moore, H.-P. H. (1991) Reconstitution of constitutive secretion using semi-intact cells Regulation by GTP but not calcium. /. Cell Biol. 112, 39-54. 

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