Deficiency in lysosomal enzyme secretion is associated with upregulation of phosphatidylinositol 4-phosphate in tetrahymena.
A variety of lower eukaryotes and certain mammalian cells are known to constitutively secrete lysosomal hydrolases. Recent studies in Tetrahymena have shown that phosphatidylinositol 3-phosphate regulates the proper secretion of lysosomal enzymes at the level of phagolysosome formation. We extend these findings by studying the secretion-deficient strain MS-1 of Tetrahymena thermophila, which possess phosphatidylinositol levels similar to wild type. However, steady-state levels of phosphatidylinositol 4-phosphate (PtdIns4P) were found to be doubled in this strain compared with wild type as shown by in vivo [3H]inositol labeling and high-performance liquid chromatography analysis. The increased PtdIns4P levels in MS-1 cells were unrelated to the upregulation of total phosphatidylinositol phosphate induced by hyperosmotic stress because this treatment resulted in a similar increase of PtdIns4P in MS-1 and wild-type cells. Hyperosmotic stress did not affect secretion in either of the two types of cells. On the other hand, under conditions of wortmannin-induced hypersecretion in wild-type cells, MS-1 cells developed a highly vacuolated phenotype while secretion was not induced. Importantly, comparative analysis of wild-type and MS-1 cells under wortmannin treatment showed that PtdIns4P levels were differentially regulated in the two strains. These results collectively suggest that PtdIns4P turnover in Tetrahymena is linked to lysosome secretion.
Deli
Dimitra
D
Laboratory of Biochemistry, Department of Chemistry, University of Athens, Zografou, 15771 Athens, Greece.
Leondaritis
George
G
Tiedtke
Arno
A
Galanopoulou
Dia
D
D000135:Acid Phosphatase / Q000378:metabolism; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002855:Chromatography, Thin Layer; D008247:Lysosomes / Q000201:enzymology*; D009154:Mutation; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D013768:Tetrahymena / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D000077191:Wortmannin
D000730:Androstadienes; D018129:Phosphatidylinositol Phosphates; D010726:Phosphodiesterase Inhibitors; C055525:phosphatidylinositol 3-phosphate; C037178:phosphatidylinositol 4-phosphate; D000135:Acid Phosphatase; D010738:Type C Phospholipases; D000077191:Wortmannin