Characterization by chromatofocusing of estrogen receptors from rat mammary tumor MTW9.
The estrogen receptor (ER) from rat mammary tumor MTW9-D, which is sensitive to ovariectomy, could be separated by chromatofocusing (CF) into two peaks specifically binding 3H-estradiol, focusing at pH 6.8 (peak A) and pH 6.0 (peak B). The ER from MTW9-MtT tumor, which is resistant to ovariectomy, presented only one peak, focusing at pH 6.0 (peak B). The peaks presented similar sedimentation coefficients (3.5s) with peak B being slightly larger than peak A. Regardless of the tumor sensitivity to hormonal manipulation, the two peaks presented similar molecular weights as shown by immunostaining of Western blots: a major duplex component of 70 kilodaltons (kd), and single bands at 48, 36, and 35 kd. The bands under 70 kd could be proteolytic products; however, the pattern could not be changed by addition of molybdate, leupeptin, or phenylmethylsulfonylfluoride. The pattern was reproducible in experiments done at different intervals of time or when rechromatofocusing. The peaks presented different isoelectric points: peak A, pH 6.8; peak B, pH 6.0. Also, they had different DNA binding abilities: peak A bound quantitatively to DNA, while peak B bound only 20%. Peak A was always present in tumors responsive to ovariectomy, a fact that suggests this ER component could be a marker for the responsiveness to hormonal therapy.
Platica
M
M
Department of Surgery, Mount Sinai Medical School, New York, NY 10029.
Doody
J
J
Platica
O
O
Cryan
J G
JG
Hollander
V P
VP
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D002852:Chromatography, Ion Exchange / Q000379:methods; D004247:DNA / Q000378:metabolism; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism*; D008970:Molecular Weight; D010052:Ovariectomy; D051381:Rats; D011960:Receptors, Estrogen / Q000032:analysis*
D011960:Receptors, Estrogen; D004247:DNA