Rapid secretion by a nonclassical pathway of overexpressed mammalian mitochondrial rhodanese.
Rhodanese is a small (33 kDa) monomeric sulfurtransferase which is synthesized on cytoplasmic ribosomes and imported into the mitochondrial matrix without cleavage of its amino terminus. When we transfected mammalian cell lines with rhodanese cDNA under the control of an efficient viral promoter, up to 40% of the overexpressed protein was secreted into the medium. This secretion was not the result of cell lysis, did not occur via the endoplasmic reticulum, and did not require the amino-terminal mitochondrial import signal. Addition of a carboxyl-terminal peptide extension did not block secretion, nor did a number of inhibitors of cellular sorting processes. Rhodanese polypeptide is known to associate with chaperonin proteins. In the absence of available mitochondrial import sites, such a complex in the cytoplasm of transfected cells could deliver unfolded rhodanese to export pores on the inner surface of the plasma membrane. This mechanism could contribute to the nonclassical secretion of cytoplasmically synthesized interleukins, growth factors, and lectins.
Department of Biochemistry, University of Texas Health Science Center at San Antonio 78284-7877.
I S
IS
Sloan
P M
PM
Horowitz
J M
JM
Chirgwin
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002451:Cell Compartmentation; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship; D013884:Thiosulfate Sulfurtransferase / Q000378:metabolism*
D006023:Glycoproteins; D011994:Recombinant Proteins; D013884:Thiosulfate Sulfurtransferase