Chris Mayne, W. Toy, K. Carlson, T. Bhatt, S. W. Fanning, G. L. Greene, B. S.
Katzenellenbogen, S. Chandarlapaty, J. A. Katzenellenbogen, and Emad
Tajkhorshid.
Defining the energetic basis for a conformational switch mediating
ligand-independent activation of mutant estrogen receptors in breast cancer.
Molecular Cancer Research, 19:1559-1570, 2021.
MAYN2021-ET
Although most primary estrogen receptor (ER)-positive breast cancers respond well to endocrine therapies, many
relapse later as metastatic disease due to endocrine therapy resistance. Over one third of these are associated
with mutations in the ligand-binding domain (LBD) that activate the receptor independent of ligand. We have used
an array of advanced computational techniques rooted in molecular dynamics simulations, in concert with and
validated by experiments, to characterize the molecular mechanisms by which specific acquired somatic point
mutations give rise to ER constitutive activation. By comparing structural and energetic features of
constitutively active mutants and ligand-bound forms of ER-LBD with unliganded wild-type (WT) ER, we
characterize a spring force originating from strain in the Helix 11-12 loop of WT-ER, opposing folding of Helix 12
into the active conformation and keeping WT-ER off and disordered, with the ligand-binding pocket open for rapid
ligand binding. We quantify ways in which this spring force is abrogated by activating mutations that latch
(Y537S) or relax (D538G) the folded form of the loop, enabling formation of the active conformation without
ligand binding. We also identify a new ligand-mediated hydrogen-bonding network that stabilizes the active, ligand-
bound conformation of WT-ER LBD, and similarly stabilizes the active conformation of the ER mutants in the
hormone-free state. IMPLICATIONS: Our investigations provide deep insight into the energetic basis for the
structural mechanisms of receptor activation through mutation, exemplified here with ER in endocrine-resistant
metastatic breast cancers, with potential application to other dysregulated receptor signaling due to driver
mutations.
