Constitutive Secretion in Tetrahymena thermophila

Abstract

The growth, survival, and life cycle progression of the freshwater ciliated protozoan Tetrahymena thermophila are responsive to protein signals thought to be released by constitutive secretion. In addition to providing insights about ciliate communication, studies of constitutive secretion are of interest for evaluating the utility of T. thermophila as a platform for the expression of secreted protein therapeutics. For these reasons, we undertook an unbiased investigation of T. thermophila secreted proteins using wild-type and secretion mutant strains. Extensive tandem mass spectrometry analyses of secretome samples were performed. We identified a total of 207 secretome proteins, most of which were not detected in a set of abundant whole-cell protein identifications. Numerous proteases and other hydrolases were secreted from cells grown in rich medium but not cells transferred to a nutrient starvation condition. On the other hand, we detected the starvation-enhanced secretion of a small number of cytosolic proteins, suggestive of an exosome-like pathway in T. thermophila. Subsets of proteins from the T. thermophila regulated secretion pathway were detected with differential representation across strains and culture conditions. Finally, many secretome proteins had a predicted N-terminal signal sequence but no other annotated characteristic or functional classification. Our work provides the first comprehensive analysis of secreted proteins in T. thermophila and establishes the groundwork for future studies of constitutive protein secretion biology and biotechnology in ciliates.

Investigation of a recombinant SMN protein delivery system to treat spinal muscular atrophy

“…Secretion is initiated following cleavage of the signal peptide and is completed by molecular trafficking events, which deliver the protein to the plasma membrane [40].…”

Membrane Dynamics at the Nuclear Exchange Junction during Early Mating (One to Four Hours) in the Ciliate Tetrahymena thermophila

“…It is intriguing to speculate that in Tetrahymena, shed microvesicles may somehow be involved in cell-cell signaling as conjugation is initiated. It is significant that constitutive secretion involving some form of extracellular microvesicles has been demonstrated in T. thermophila (46).…”

Conservation and Innovation in Tetrahymena Membrane Traffic: Proteins, Lipids, and Compartments

“…A proteomic analysis of T. thermophila culture supernatants has recently supplied the first relatively comprehensive view of what this unicellular protest is releasing into its environment(Madinger et al, 2010). That list includes 207 proteins including many hydrolytic enzymes as well as novel proteins of unknown function, with the cohort of secreted proteins changing significantly depending on whether cells were incubated under nutritive vs starvation conditions.…”

“…Fourth, endocytic membrane recovery also occurs upon phagosome fusion, at a cortical site called the cytoproct(Allen and Wolf, 1979). Similarly, Tetrahymena secrete proteins by at least 3 different routes: a pathway of rapid constitutive release of newly-synthesized proteins (for which the vesicular carriers have not been identified)(Bowman and Turkewitz, 2001; Madinger et al, 2010); regulated exocytosis from docked mucocysts(Turkewitz, 2004), and; release of hydrolytic enzymes via lysosome exocytosis(Kiy et al, 1993). There is also indirect evidence for cytoplasmic protein release via an exosome-like mechanism(Madinger et al, 2010).…”

“…Similarly, Tetrahymena secrete proteins by at least 3 different routes: a pathway of rapid constitutive release of newly-synthesized proteins (for which the vesicular carriers have not been identified)(Bowman and Turkewitz, 2001; Madinger et al, 2010); regulated exocytosis from docked mucocysts(Turkewitz, 2004), and; release of hydrolytic enzymes via lysosome exocytosis(Kiy et al, 1993). There is also indirect evidence for cytoplasmic protein release via an exosome-like mechanism(Madinger et al, 2010). This list understates the complexity of the pathways of cell surface delivery, since for example there is also vesicle trafficking from the cytoproct (the site of phagosome exocytosis) to the oral apparatus(Allen and Fok, 1980; Bright et al, 2010).…”