RESUMO
p21-activated kinases (Paks) are Cdc42/Rac-activated serine-threonine protein kinases that regulate several key cancer-relevant signaling pathways, such as the Mek/Erk, PI3K/Akt and Wnt/b-catenin signaling pathways. Pak1 is frequently overexpressed and/or hyperactivated in different human cancers, including human breast, ovary, prostate and brain cancer, due to amplification of the PAK1 gene in an 11q13 amplicon. Genetic or pharmacological inactivation of Pak1 has been shown to reduce proliferation of different cancer cells in vitro and reduce tumor progression in vivo. In this work, we examined the roles of Pak1 in cellular and animal models of PAK1-amplified ovarian cancer. We found that inhibition of Pak1 leads to decreased proliferation and migration in PAK1-amplified/overexpressed ovarian cancer cells, and has no effect in cell that lack such amplification/overexpression. Further, we observed that loss of Pak1 function causes 11q13-amplified ovarian cancer cells to arrest in the G2/M phase of the cell cycle. This arrest correlates with activation of p53 and p21(Cip) and decreased expression of cyclin B1. These findings suggest that small-molecule inhibitors of Pak1 may have a therapeutic role in the ~25% of ovarian cancers characterized by PAK1 gene amplification.
Assuntos
Proliferação de Células/genética , Neoplasias Ovarianas/genética , Quinases Ativadas por p21/biossíntese , Animais , Ciclo Celular/genética , Pontos de Checagem do Ciclo Celular/genética , Ciclina B1/biossíntese , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Camundongos , Neoplasias Ovarianas/patologia , Transdução de Sinais , Proteína Supressora de Tumor p53/biossíntese , Ensaios Antitumorais Modelo de Xenoenxerto , Quinases Ativadas por p21/antagonistas & inibidores , Quinases Ativadas por p21/genéticaRESUMO
The activation of receptor tyrosine kinases, particularly ErbB2, has an important role in the genesis of breast cancer. ErbB2 kinase activity promotes Ras-mediated stimulation of downstream protein kinase cascades, including the Ras/Raf-1/MAPK/ERK kinase (Mek)/extracellular signal-regulated kinase (Erk) pathway, leading to tumor cell growth and migration. Signaling through the Ras-Erk pathway can be influenced by p21-activated kinase-1 (Pak1), an effector of the Rho family GTPases Rac and Cdc42. In this study, we asked if ErbB2 expression correlates with Pak1 and Erk activity in human breast cancer specimens, and if Pak1 signaling is required for ErbB2 transformation in a three-dimensional (3D) in vitro setting and in xenografts. We found a correlation between ErbB2 expression and activation of Pak in estrogen receptor-positive human breast tumor samples and observed that in 3D cultures, activation of Rac-Pak1 pathway by ErbB2 homodimers induced growth factor-independent proliferation and promoted disruption of 3D mammary acinar-like structures through activation of the Erk and Akt pathways. Further, we found that inhibition of Pak1 by small molecules compromised activation of Erk and Akt, resulting in reversion of the malignant phenotype and restoration of normal acinar architecture. Finally, ErbB2-amplified breast cancer cells expressing a specific Pak inhibitor showed delayed tumor formation and downregulation of Erk and Akt signaling in vivo. These data imply that the Rac-Pak pathway is vital to ErbB2-mediated transformation and that Pak inhibitors represent plausible drug targets in breast cancers in which ErbB2 signaling is activated.
Assuntos
Neoplasias da Mama/metabolismo , Transformação Celular Neoplásica/metabolismo , Receptor ErbB-2/metabolismo , Transdução de Sinais/fisiologia , Quinases Ativadas por p21/metabolismo , Animais , Western Blotting , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Transformação Celular Neoplásica/efeitos dos fármacos , Transformação Celular Neoplásica/genética , Inibidores Enzimáticos/farmacologia , MAP Quinases Reguladas por Sinal Extracelular/genética , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Feminino , Imunofluorescência , Humanos , Imuno-Histoquímica , Camundongos , Camundongos SCID , Proteínas Proto-Oncogênicas c-akt/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Receptor ErbB-2/genética , Transdução de Sinais/efeitos dos fármacos , Análise Serial de Tecidos , Ensaios Antitumorais Modelo de Xenoenxerto , Quinases Ativadas por p21/genéticaRESUMO
We studied the effects of oestradiol and progesterone on progesterone receptor (PR) isoform content in the brain of ovariectomized rats and in intact rats during the oestrous cycle by Western blot analysis. In the hypothalamus and the preoptic area of ovariectomized rats, PR-A and PR-B content was increased by oestradiol, whereas progesterone significantly diminished the content of both PR isoforms after 3 h of treatment in the hypothalamus, but not in the preoptic area. In the hippocampus, only PR-A content was significantly increased by oestradiol while progesterone significantly diminished it after 12 h of treatment. In the frontal cortex, no treatment significantly modified PR isoform content. During the oestrous cycle, the lowest content of PR isoforms in the hypothalamus was observed on diestrus day and, by contrast, in the preoptic area, the highest content of both PR isoforms was observed on diestrus day. We observed no changes in PR isoform content in the hippocampus during the oestrous cycle. These results indicate that the expression of PR isoforms is differentially regulated by sex steroid hormones in a regionally specific manner.
