First paragraph (this article has no abstract) Subcellular targeting of proteins in host cells is one of the most important issues in protein production. Stability, folding, and post-translational modifications depend on where proteins are sorted. Besides secretion, ER appears as an efficient compartment to accumulate proteins, as demonstrated by the frequent use of K/HDEL fused to the C-terminus of a protein to retain and accumulate recombinant proteins in the endoplasmic reticulum (ER) of the cell hosts.Peer reviewed