Selective Delivery of Secretory Cargo in Golgi‐Derived Carriers of Nonepithelial Cells

Abstract

In epithelial cells, soluble cargo proteins destined for basolateral or apical secretion are packaged into distinct trans-Golgi network-derived transport carriers. Similar carriers, termed basolateral-and apical-like, have been observed in nonepithelial cells using ectopically expressed membrane marker proteins. Whether these cells are capable of selectively packaging secretory proteins into distinct carriers is still an open question. Here, we have addressed this issue by analyzing the packaging and transport of secretory human chromogranin B fusion proteins using a green fluorescent protein-based high-resolution, dual-color imaging technique. We were able to show that these secretory markers were selectively packaged at the Golgi into tubular/vesicular-like transport carriers containing basolateral membrane markers, resulting in extensive cotransport. In contrast, deletion mutants of the human chromogranin B fusion proteins lacking an N-terminal loop structure were efficiently transported in both basolateral-and apical-like carriers, the latter displaying a spherical morphology. Similarly, in polarized epithelial cells, the human chromogranin B fusion protein was secreted basolaterally and the loop-deleted analogue into both the basolateral and apical medium. These findings suggest that nonepithelial cells, like their epithelial counterparts, possess a sorting machinery capable of selective packaging of secretory cargo into distinct types of carriers.

Dense-core granules: a specific hallmark of the neuronal/neurosecretory cell phenotype

“…In previous studies on transfected CV-1 and Vero cells, the major localisation of CgA and CgB had been reported in the perinuclear GC/TGN area (Kim et al, 2001;Rustom et al, 2002). In addition, also discrete granin-positive puncta were reported to appear, however only in a fraction of the transfected cells.…”

“…In the case of CgA, and based on general ultrastructure, the corresponding organelles were defined as DCGs (Kim et al, 2001). With CgB, in contrast, the size of the organelles was large, and the DCG definition was proposed in one (Huh et al, 2003) but not in another (Rustom et al, 2002) case. In the present study the concentration of the two granins in the CG/TGN area was confirmed by co-labelling with specific markers, i.e.…”

“…and B (CgA and CgB), when expressed in non-secretory cells were reported to distribute not only to the Golgi complex/transGolgi network (GC/TGN), the area from which constitutive secretion takes place, but also to discrete organelles scattered throughout the cytoplasm (Kim et al, 2001;Rustom et al, 2002;Huh et al, 2003). At least morphologically, some of these organelles resemble typical DCGs of neurones and neurosecretory cells (Kim et al, 2001).…”

Mechanisms of eosinophil secretion: large vesiculotubular carriers mediate transport and release of granule-derived cytokines and other proteins

“…Emerging evidence has pointed to the participation of vesiculotubular carriers in different cell secretory pathways. Well-documented examples are the transport system between the endoplasmic reticulum (ER) and Golgi complex [64][65][66][67], from the endosomal system [68] or the TGN [69,70] to the plasma membrane, and along axons [71][72]. These carriers appear as vesiculotubular structures of various shapes and sizes.…”

Lumenal protein sorting to the constitutive secretory pathway of a regulated secretory cell

“…Curiously, such perturbation also inhibits secretory protein trafficking via the constitutive pathway (Wang et al, 2000), raising the hypothesis that certain lumenal proteins of the constitutive secretory pathway may also be selectively captured for entry into post-TGN transport intermediates (Rustom et al, 2002). In polarized MDCK epithelial cells where all newly synthesized secretory proteins transported to apical and basolateral media are thought to use constitutive secretion pathways, there is a precedent that at least some of these proteins may undergo selective capture by membranes of post-TGN transport intermediates (Caplan et al, 1987;Cheong et al, 1999;Kuhn et al, 2000;Martin-Belmonte et al, 2000;Martin-Belmonte et al, 2001;Urban et al, 1987;Zhang et al, 2002).…”