title: Analysis of the nuclear estrogen receptor from MCF-7 cells by limited proteolysis.
abstract: The proteolytic fragments of the nuclear estrogen receptor in the MCF-7 cell line were characterized following limited digestion with chymotrypsin and trypsin. Nuclei were isolated from cells previously exposed to 10 nM [3H]estradiol. The proteolytic digestion was performed either on the micrococcal nuclease hydrolysate or on intact nuclei. The molecular weights (Mr) were calculated from the sedimentation coefficients determined on a sucrose gradient and from the Stokes radii estimated by gel filtration. Digestion of the nuclei with micrococcal nuclease solubilized a receptor form of Mr = 151,000. This receptor form was degraded by chymotrypsin to a receptor of Mr = 33,000 and by trypsin to a receptor of Mr = 60,000. Digestion of intact nuclei with chymotrypsin solubilized a receptor form of Mr = 62,000 which dissociated in 0.4 M KCl to a receptor of Mr = 32,000. Digestion of intact nuclei with trypsin followed by micrococcal nuclease solubilized a receptor form of Mr = 75,000 which was further dissociated by 0.4 M KCl to a receptor form of Mr = 60,000. The ability of the receptor forms to bind DNA was tested using DNA-cellulose column chromatography. About 40% of the micrococcal nuclease solubilized receptor form, compared to about 7% of the chymotrypsin degraded receptor and to about 13% of the trypsin degraded receptor forms, all bound to the column and could be eluted by high salt concentrated buffer. We conclude that the nuclear estrogen receptor in the MCF-7 cell line can be partially degraded either in the micrococcal nuclease hydrolysate or in intact nuclei by chymotrypsin or trypsin generating protein moieties, probably receptor fragments of Mr = 33,000 and 60,000 respectively. Both fragments retain their estradiol binding domain and it may be hypothesized that the heavier fragment retains its chromatin binding domain.
mesh_terms: D001943:Breast Neoplasms / Q000032:analysis* / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000032:analysis / Q000378:metabolism; D002498:Centrifugation; D002918:Chymotrypsin; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D008836:Micrococcal Nuclease; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D011960:Receptors, Estrogen / Q000032:analysis* / Q000378:metabolism; D014357:Trypsin
chemical_list: D004268:DNA-Binding Proteins; D010446:Peptide Fragments; D011960:Receptors, Estrogen; D004247:DNA; D008836:Micrococcal Nuclease; D002918:Chymotrypsin; D014357:Trypsin