The ER contributes to engulfment

New results from Etienne Gagnon, Michel Desjardins (Université de Montréal, Montreal, Canada), and colleagues finally explain how a macrophage cell produces enough membrane to engulf material as large as itself—it uses large contributions of membrane from the ER. This is the first demonstration that the ER can fuse with the plasma membrane (PM).

In a previous proteomics experiment, Desjardins' group found several ER-associated proteins in phagosome preparations. But their first thought was contamination, as phagocytosis is widely considered to be a function of the PM. “This was something from the textbooks we all did not question,” Desjardins says. “It was not our aim to challenge this idea.” However, the new immunogold and immunocytochemical experiments clearly showed a distribution of ER marker proteins such as calnexin and calreticulin throughout the phagosome membrane.

Inhibition of phagocytosis...