through modulation of ER mRNA stability. Judith C Keen*, Qun Zhou, Ben Ho Park, Catherine Pettit, Kelly M Mack, Brian Blair, Keith Brenner, Nancy E Davidson. The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland, 21231; Department of Natural Sciences, University of Maryland Eastern Shore, Princess Anne, Maryland, 21853. Running title: PP2A regulation of ER alpha expression in breast cancer. *Current Address: Coriell Institute for Medical Research, Camden, New Jersey, 08106. Address correspondence to: Nancy E. Davidson, MD, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, 1650 Orleans Street, CRB Room 409, Baltimore, Maryland 21231, Tel. 410-9558489; Fax. 410-614-4073; Email: davidna@jhmi.edu