Synergistic Activation of ERα by Estrogen and Prolactin in Breast Cancer Cells Requires Tyrosyl Phosphorylation of PAK1

Abstract

Serine/threonine kinase PAK1 is activated by estrogen and plays an important role in breast cancer. However, the integration of PAK1 into the estrogen response is not fully understood. In this study, we investigated the mechanisms underlying hormone-induced activation of estrogen receptor (ERα, ESR1). We show that estrogen activated PAK1 through both the ERα and GPER1 membrane receptors. Estrogen-dependent activation of PAK1 required the phosphorylation of tyrosine residues by Etk/Bmx and protein kinase A (PKA) within an assembled signaling complex comprising pTyr-PAK1, Etk/Bmx, the heterotrimer G-protein subunits Gβ1, Gγ2 and/or Gγ5, PAK-associated guanine nucleotide exchange factor (βPIX, ARHGEF7), and PKA. Moreover, the PKA RIIβ subunit is a direct target of PAK1, and thus in response to estrogen, the activated pTyr-PAK1 complex reciprocally potentiated PKA activity, suggesting a positive feedback mechanism. We also demonstrate that PKA phosphorylated Ser305-ERα in response to estrogen, but pTyr-PAK1 phosphorylated Ser305-ERα in response to prolactin (PRL), implying that maximal ERα phosphorylation is achieved when cells are exposed to both PRL and estrogen. Furthermore, S305-ERα activation led to enhanced phosphorylation of Ser118-ERα and promoted cell proliferation and tumor growth. Together, these data strongly support a critical interplay between PRL and estrogen via PAK1, and suggest that ligand-independent activation of ERα through PRL/PAK1 may impart resistance to anti-estrogen therapies.

PAK1 translocates into nucleus in response to prolactin but not to estrogen

“…MCF-7 clones stably overexpressing vector, HA-tagged PAK1 WT and PAK1 Y3F (described in [20]) were maintained in DMEM (Corning Cellgro) supplemented with 10% FBS (Sigma-Aldrich). Deprivation media consisted of DMEM supplemented with 1% bovine serum albumin (Sigma-Aldrich).…”

“…In attempt to define the role of PAK1 in the synergistic effect of PRL and estrogen (E2) on breast cancer cell proliferation, we have recently demonstrated that PAK1 phosphorylates Ser305 of estrogen receptor α (ERα) in response to PRL while protein kinase A (PKA) phosphorylates the same site in response to E2 [20]. In this study we provide evidence that PRL activates and promotes PAK1 translocation into the nucleus in ligand- and phospho-tyrosyl-dependent manner.…”

Upregulation of P21-Activated Kinase 1 (PAK1)/CREB Axis in Squamous Non-Small Cell Lung Carcinoma

“…Moreover, PAK1 expression is upregulated in prostate cancer, and treatment with the mTOR inhibitor rapamycin slowed cancer cell proliferation by inhibiting PAK1 expression [4]. Furthermore, in human breast cancer cells, PAK1 can mediate cell proliferation and tumor growth, with prolactin treatment triggering PAK1-mediated estrogen receptor-α phosphorylation [5].…”

O efeito da prolactina na migração de células de câncer de mama pela remodelação da actina no citoesqueleto

“…Estes mecanismos podem também ser ativados pela prolactina pela ação da proteína JAK (Das e Vonderhaar, 1996;Sato et al, 2013). Além disso, alguns autores sugerem que os dois hormônios poderiam ter ação sinérgica, o que incrementaria a migração celular (Oladimeji et al, 2016).…”

“…Nesse tipo de câncer, a modificação do alinhamento das fibras colágenas (que se tornam mais perpendiculares na superfície da célula) é fator preditivo de sua agressividade (Barcus et al, 2013) que também é alvo da prolactina (Barcus et al, 2015). Possivelmente, a PRL pode ter uma ação sinérgica ao estrogênio na MEC (Oladimeji et al, 2016).…”