C-terminal truncation of alpha-COP affects functioning of secretory organelles and calcium homeostasis in Hansenula polymorpha.

Maria B Chechenova, Nina V Romanova, Alexander V Deev, Anna N Packeiser, Vladimir N Smirnov, Michael O Agaphonov, Michael D Ter-Avanesyan

Journal: Eukaryotic cell 2004;3(1):52-60

PMID: 14871936

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Abstract

In eukaryotic cells, COPI vesicles retrieve resident proteins to the endoplasmic reticulum and mediate intra-Golgi transport. Here, we studied the Hansenula polymorpha homologue of the Saccharomyces cerevisiae RET1 gene, encoding alpha-COP, a subunit of the COPI protein complex. H. polymorpha ret1 mutants, which expressed truncated alpha-COP lacking more than 300 C-terminal amino acids, manifested an enhanced ability to secrete human urokinase-type plasminogen activator (uPA) and an inability to grow with a shortage of Ca2+ ions, whereas a lack of alpha-COP expression was lethal. The alpha-COP defect also caused alteration of intracellular transport of the glycosylphosphatidylinositol-anchored protein Gas1p, secretion of abnormal uPA forms, and reductions in the levels of Pmr1p, a Golgi Ca2+-ATPase. Overexpression of Pmr1p suppressed some ret1 mutant phenotypes, namely, Ca2+ dependence and enhanced uPA secretion. The role of COPI-dependent vesicular transport in cellular Ca2+ homeostasis is discussed.

Address: Institute of Experimental Cardiology, Cardiology Research Center, 121552 Moscow, Russia.

DOI: 10.1128/EC.3.1.52-60.2004