SEL1L, highly similar to the C elegans sel-1 gene, is a recently cloned human gene whose function is under investigation. SEL1L is differentially expressed in tumors and normal tissues and seems to play a role in tumor growth and aggressiveness. It may be an important negative regulator of the "notch" pathway which acts as a key regulator of the cellular proliferation and specification processes in both vertebrates and invertebrates. SEL1L may function in the protein degradation processes through the ubiquitin-proteosome system and perhaps in regulating important pathways such TGF-beta.

It is ubiquitously expressed only in fetal and neoplastic tissues. In normal adult tissues is highly expressed in the acini and in the alpha cells of the pancreas; in general it is highly represented in secretory cells such as plasma cells.