The endoplasmic reticulum (ER) is a very important multi-functional organelle in eukaryotic cells. While completing the basic physiological functions, the endoplasmic reticulum becomes a pivotal platform for coordinated signal transduction with its large membrane structure. The endoplasmic reticulum is a site for lipid and sterol synthesis, maintenance of Ca2+ dynamic balance, protein synthesis and folding, and post-translational modification, as well as lipid and steroid metabolism.