Abstract
Several physiologically important proteins lack a classical secretory signal sequence, yet they are secreted from cells. To investigate the secretion mechanism of such proteins, a representative mammalian protein that is exported by a nonclassical mechanism, galectin-1, has been expressed in yeast. Galectin-1 is exported across the yeast plasma membrane, and this export does not require the classical secretory pathway nor the yeast multidrug resistance-like protein Ste6p, the transporter for the peptide a factor. A screen for components of the export machinery has identified genes that are involved in nonclassical export. These findings demonstrate a new pathway for protein export that is distinct from the classical secretory pathway in yeast.
Highlights
Several physiologically important proteins lack a classical secretory signal sequence, yet they are secreted from cells
Mammalian cells produce a variety of proteins that lack a secretory signal sequence, yet they are exported from cells, often after posttranslational processing
The release of angiogenic basic FGF (bFGF) is of medical importance, since angiogenesis is associated with metastasis, and growth of tumor cells in vivo can be inhibited by antibFGF-immunoneutralizing anitbodies (Hori et al, 1991)
Summary
Several physiologically important proteins lack a classical secretory signal sequence, yet they are secreted from cells. Mammalian cells produce a variety of proteins that lack a secretory signal sequence, yet they are exported from cells, often after posttranslational processing (reviewed by Muesch et al, 1990; Mignatti and Rifkin, 1991; Rubartelli and Sitia, 1991; Kuchler and Thorner, 1992) Examples of such proteins are interleukin-lf (Rubartelli et al, 1990; Siders and Mizel, 1995), basic FGF (bFGF) 1 (Florkiewicz et al, 1995), thioredoxin (Rubartelli et al, 1992), and galectin-1 (Cooper and Barondes, 1990).
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