Membrane Progestin Receptor Beta (MPRb)

LMPB1 has 8 putative transmembrane regions and an intracellular N terminus that contains a leucine-rich motif. The protein is translated from the second of 2 possible start codons, and the 3-prime untranslated region contains 5 potential polyadenylation sites. Northern blot analysis detected 5- and 3-kb transcripts expressed predominantly in whole brain and in all adult brain regions tested. Similar results were found in mouse, except that mouse testis showed a 2-kb transcript. Northern blot analysis was unable to detect LMPB1 expression in human or mouse fetal tissues, including brain. Colocalization of cathepsin D and LMPB1 was also found by subcellular fractionation, and Triton X-114 phase separation confirmed that LMPB1 is an integral membrane protein.