S-PALMITOYLATION CONTROLS CELLULAR LOCALIZATION AND NON GENOMIC FUNCTIONS OF ESTROGEN RECEPTOR a

Estrogen receptor (ER)a-mediated non genomic events are now defined as necessary and sufficient for 17b-estradiol (E2)-induced cell cycle-regulating genes (e.g., cyclin D1) and G1/S phase transition. Although ERa interaction with specific membrane proteins and ERa lipid modifications have been proposed for ERa membrane localization, the biochemical bases for ERa interaction with the plasma membrane are unknown. As a potential mechanism, we postulated that S-palmitoylation of the Cys447 residue may explain the ability of ERa to associate to plasma membrane making possible E2-dependent rapid functions. Cell lines expressing transfected or endogenous human ERa (HeLa and HepG2, respectively) or the ERa non-palmitoylable Cys447Ala mutant transfected in HeLa cells have been used as experimental models. Here, we report direct evidence that ERa is a palmitoylated protein. The mutation of the Cys447 residue to Ala impairs ERa palmitoylation and results in the loss of ERa plasma membrane localization and interaction with caveolin-1. In turn, E2-induced rapid non-genomic signals (i.e., ERK and AKT activation, cyclin D1 promoter activity and DNA synthesis) are also prevented. On the other hand, the Cys447Ala mutation significantly decreases the E2-induced transactivation of an estrogen responsive element construct probe. Remarkably, both ERa palmitoylation and its interaction with caveolin-1 are reduced by E2 in time and dose dependent fashion. Similar results have been obtained in HepG2 cells. As a whole, these data indicate that palmitoylation can be regarded as a regulatory device enabling ERa to initiate non-genomic signal transduction pathways that lead cell to proliferate.