Differential targeting of recombinant fibronectins in AtT-20 cells based on their efficiency of aggregation.
In pituitary-derived AtT-20 cells, recombinant fibronectin containing the N-terminal matrix assembly domain and the C-terminal half of fibronectin does not follow the regulated secretory pathway but instead concentrates in distinct organelles prior to secretion. These organelles are larger than the dense-core granules and localize to the cell body at sites that differ from lysosomes, endosomes and endoplasmic reticulum. Unlike the dense-core granules, their discharge is not stimulated by 8-bromo-cyclic-AMP or phorbol esters. The kinetics of intracellular transport and secretion of the recombinant fibronectin suggest that it is present in a post-Golgi pool that turns over more slowly than constitutive vesicles. Indeed, the fibronectin-containing organelles disappear with a half-time of 3 hours after inhibiting protein synthesis. Presence of the organelles correlates with intracellular aggregation of dimeric fibronectin polypeptides. The organelles are absent in cells expressing monomeric recombinant fibronectin (lacking C-terminal dimerization sites) or the C-terminal half of fibronectin (which dimerizes but lacks the N-terminal matrix assembly domain), both of which aggregate less efficiently than dimeric fibronectin. Instead, the latter polypeptides enter the dense-core granules. Thus while the formation of the fibronectin-containing organelles may require efficient aggregation, it may not require a specific structural signal. Moreover, efficient aggregation is not necessarily a prerequisite for following the regulated pathway.
Castle
A M
AM
Department of Cell Biology, University of Virginia Health Sciences Center, Charlottesville 22908, USA. amc3c@virginia.edu
Schwarzbauer
J E
JE
Wright
R L
RL
Castle
J D
JD
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002449:Cell Aggregation / Q000502:physiology; D002460:Cell Line; D005353:Fibronectins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D015388:Organelles / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D001615:beta-Endorphin / Q000378:metabolism
D005353:Fibronectins; D011994:Recombinant Proteins; D001615:beta-Endorphin; D000324:Adrenocorticotropic Hormone