RESUMO
Metastatic Breast Cancer has a poor 25% survival rate and currently there are no clinical therapeutics which target metastasis. 'Migrastatics' are a new drug class which target migration pathway effector proteins in order to inhibit cancer cell invasion and metastasis. The p21-activated kinases (PAKs) are essential drivers of breast cancer cell migration and invasion through their regulation of actin cytoskeletal dynamics. Therefore, the PAKs present as attractive migrastatic candidates. Here we review how PAKs regulate distinct aspects of breast cancer actin dynamics focussing on cytoskeletal reorganisation, cell:matrix adhesion, actomyosin contractility and degradative invasion. Lastly, we discuss the introduction of PAK migrastatics into the well-honed breast cancer clinical pipeline.
Assuntos
Actinas , Neoplasias da Mama , Actinas/metabolismo , Neoplasias da Mama/metabolismo , Citoesqueleto/metabolismo , Feminino , Humanos , Quinases Ativadas por p21/genética , Quinases Ativadas por p21/metabolismoRESUMO
P21-activated kinases (PAKs) are important regulators of cell motility and morphology. It has been challenging to interrogate their functions because cells adapt to genetic manipulation of PAK, and because inhibitors act on multiple PAK isoforms. Here we describe genetically encoded PAK1 analogues that can be selectively activated by the membrane-permeable small molecule rapamycin. An engineered domain inserted away from the active site responds to rapamycin to allosterically control activity of the PAK1 isoform. To examine the mechanism of rapamycin-induced PAK1 activation, we used molecular dynamics with graph theory to predict amino acids involved in allosteric communication with the active site. This analysis revealed allosteric pathways that were exploited to generate kinase switches. Activation of PAK1 resulted in transient cell spreading in metastatic breast cancer cells, and long-term dendritic spine enlargement in mouse hippocampal CA1 neurons.
Assuntos
Regulação Alostérica/fisiologia , Quinases Ativadas por p21/metabolismo , Regulação Alostérica/efeitos dos fármacos , Regulação Alostérica/genética , Animais , Região CA1 Hipocampal/metabolismo , Domínio Catalítico/efeitos dos fármacos , Domínio Catalítico/genética , Linhagem Celular Tumoral , Movimento Celular/efeitos dos fármacos , Movimento Celular/genética , Movimento Celular/fisiologia , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Humanos , Técnicas In Vitro , Camundongos , Ratos , Ratos Sprague-Dawley , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Transdução de Sinais/fisiologia , Sirolimo/farmacologia , Quinases Ativadas por p21/genéticaRESUMO
P21-activated kinase 4 (PAK4) is a Cdc42 effector protein thought to regulate cell adhesion disassembly in a kinase-dependent manner. We found that PAK4 expression is significantly higher in high-grade human breast cancer patient samples, whereas depletion of PAK4 modifies cell adhesion dynamics of breast cancer cells. Surprisingly, systematic analysis of PAK4 functionality revealed that PAK4-driven adhesion turnover is neither dependent on Cdc42 binding nor kinase activity. Rather, reduced expression of PAK4 leads to a concomitant loss of RhoU expression. We report that RhoU is targeted for ubiquitination by the Rab40A-Cullin 5 complex and demonstrate that PAK4 protects RhoU from ubiquitination in a kinase-independent manner. Overexpression of RhoU rescues the PAK4 depletion phenotype, whereas loss of RhoU expression reduces cell adhesion turnover and migration. These data support a new kinase-independent mechanism for PAK4 function, where an important role of PAK4 in cellular adhesions is to stabilize RhoU protein levels. Thus, PAK4 and RhoU cooperate to drive adhesion turnover and promote cell migration.