Appearance of 50,000- and 52,000-dalton cAMP receptor proteins in the nucleoli of regressing MCF-7 human breast cancer upon estrogen withdrawal.
Affinity purified antibodies to type I and type II regulatory subunits (RI and RII, respectively) of cAMP-dependent protein kinase were utilized to identify and localize the cAMP receptor proteins in growing vs regressing MCF-7 tumors in nude mice. In the nuclear extracts of growing tumors the RI antibody immunoprecipitated cAMP receptor protein of 47,000 daltons, whereas the RII antibody precipitated 44,000- and 34,000-dalton cAMP receptor proteins. Following estrogen withdrawal, new species of cAMP receptor proteins with molecular weights of 50,000 and 52,000 appeared in the nuclei of regressing tumors. The 50,000- and 52,000-dalton proteins were specifically precipitated by the RII antibody but not by RI antibody. Indirect immunofluorescence revealed that during regression of MCF-7 tumors, the intensity of immunofluorescence of RII antibody crossreacting cAMP binding proteins dramatically increased in the nucleoli whereas the immunofluorescence of RI remained the same. These results suggest a regulatory role of RII in mammary cancer regression.
D000818:Animals; D001943:Breast Neoplasms / Q000503:physiopathology*; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D008970:Molecular Weight; D009368:Neoplasm Transplantation; D011953:Receptors, Cyclic AMP / Q000378:metabolism*; D014183:Transplantation, Heterologous
D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D004967:Estrogens; D011953:Receptors, Cyclic AMP