Polytopic transmembrane protein that inhibits regulated intramembrane proteolysis (RIP) of CREB3L1, inhibiting its activation and the induction of collagen synthesis (PubMed:25310401, PubMed:27499293). In response to ceramide, which alters TM4SF20 membrane topology, stimulates RIP activation of CREB3L1 (PubMed:27499293). Ceramide reverses the direction through which transmembrane helices are translocated into the endoplasmic reticulum membrane during translation of TM4SF20, this mechanism is called 'regulated alternative translocation' (RAT) and regulates the function of the transmembrane protein (PubMed:27499293). . This is the function of ENSG00000168955 (TM4SF20, transmembrane 4 L six family member 20).