title: MUC1 is a substrate for gamma-secretase.
abstract: Understanding the underlying mechanisms by which a normal cell avoids the oncogenic potential of MUC1 signaling requires further definition of the pathways by which the MUC1 cytoplasmic tail is processed in both normal and tumor-derived cells. In the present study we describe the processing pathway initiated by TACE/ADAM17 cleavage of MUC1. Utilizing the human uterine epithelial cell line, HES, derived from normal endometrium, we show that endogenous full length MUC1 undergoes regulated intramembranous proteolysis mediated by presenillin-dependent gamma-secretase. Cytokine-stimulated HES cells exposed to gamma-secretase inhibitors accumulated a membrane-associated 15 kDa fragment of the MUC1 C-terminal subunit (CTF15). Inhibitors of TACE/ADAM17-mediated shedding inhibited accumulation of MUC1-CTF15 and MUC1 ectodomain release to a similar extent consistent with MUC1-CTF15 being a product of TACE/ADAM17 action. Reduction of catalytically active gamma-secretase complex by nicastrin siRNA treatment also resulted in CTF15 accumulation. Furthermore, mature nicastrin, the substrate receptor for gamma-secretase, co-immunoprecipitated with CTF15 in the presence of gamma-secretase inhibitors indicating the formation of CTF15: nicastrin complexes. MUC1-CTF15 accumulation in response to gamma-secretase inhibition was demonstrated in both normal and tumor-derived cells from humans and mice indicating that this processing pathway exists in many cell contexts. We did not detect products of MUC1 cleavage by gamma-secretase in the presence of various proteasomal inhibitors indicating that subsequent degradation is either non-proteasomal or extremely efficient. We suggest that this efficient pathway attenuates potential signaling mediated by cytoplasmic tail fragments.
authors.affiliation: Department of Biological Sciences, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Joanne
authors.initials: J
authors.lastname: Julian
authors.forename: Neeraja
authors.initials: N
authors.lastname: Dharmaraj
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Carson
mesh_terms: D051722:ADAM Proteins / Q000378:metabolism; D000072198:ADAM17 Protein; D053829:Amyloid Precursor Protein Secretases / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D016207:Cytokines / Q000378:metabolism; D019281:Dimerization; D010064:Embryo Implantation; D004717:Endometrium / Q000378:metabolism*; D005260:Female; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry; D051379:Mice; D018396:Mucin-1 / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015398:Signal Transduction
chemical_list: D016207:Cytokines; C060192:MUC1 protein, human; D008562:Membrane Glycoproteins; D018396:Mucin-1; C413604:nicastrin protein; D053829:Amyloid Precursor Protein Secretases; D051722:ADAM Proteins; D000072198:ADAM17 Protein; C000606462:ADAM17 protein, human; C000606463:Adam17 protein, mouse; D046988:Proteasome Endopeptidase Complex