Involved in the selective transport and maturation of TGF-alpha family proteins. Interacts with AREG immature precursor and with immature TGFA, i.e. with a prosegment and lacking full N-glycosylation, but not with the fully N-glycosylated form. In the Golgi apparatus, may form a complex with GORASP55 and transmembrane TGFA. Located primarily in the ER; may cycle between the ER and the Golgi apparatus. Highly expressed in heart, liver, skeletal muscle, pancreas, adrenal medulla and cortex, thyroid, testis, spleen, appendix, peripheral blood lymphocytes and bone marrow. Lower expression found in brain, placenta, lung, kidney, ovary, small intestine, stomach, lymph node, thymus and fetal liver. Expression is up-regulated in dorsolateral prefrontal cortex of patients with schizophrenia (postmortem brain study). Belongs to the cornichon family.