RESUMEN
Although mutated forms of ras are not associated with the majority of breast cancers (<5%), there is considerable experimental evidence that hyperactive Ras can promote breast cancer growth and development. Therefore, we determined whether Ras and Ras-responsive signaling pathways were activated persistently in nine widely studied human breast cancer cell lines. Although only two of the lines harbor mutationally activated ras, we found that five of nine breast cancer cell lines showed elevated active Ras-GTP levels that may be due, in part, to HER2 activation. Unexpectedly, activation of two key Ras effector pathways, the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase and phosphatidylinositol 3'-kinase/AKT signaling pathways, was not always associated with Ras activation. Ras activation also did not correlate with invasion or the expression of proteins associated with tumor cell invasion (estrogen receptor alpha and cyclooxygenase 2). We then examined the role of Ras signaling in mediating resistance to matrix deprivation-induced apoptosis (anoikis). Surprisingly, we found that ERK and phosphatidylinositol 3'-kinase/AKT activation did not have significant roles in conferring anoikis resistance. Taken together, these observations show that Ras signaling exhibits significant cell context variations and that other effector pathways may be important for Ras-mediated oncogenesis, as well as for anoikis resistance, in breast cancer. Additionally, because ERK and AKT activation are not strictly associated with Ras activation, pharmacological inhibitors of these two signaling pathways may not be the best approach for inhibition of aberrant Ras function in breast cancer treatment.
Asunto(s)
Anoicis/fisiología , Neoplasias de la Mama/patología , Proteínas ras/fisiología , Anoicis/genética , Neoplasias de la Mama/enzimología , Neoplasias de la Mama/genética , Línea Celular Tumoral , Ciclooxigenasa 2 , Receptor alfa de Estrógeno , Regulación Neoplásica de la Expresión Génica , Humanos , Isoenzimas/biosíntesis , Isoenzimas/genética , Isoenzimas/metabolismo , Sistema de Señalización de MAP Quinasas/fisiología , Proteínas de la Membrana , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Invasividad Neoplásica , Fosfatidilinositol 3-Quinasas/metabolismo , Prostaglandina-Endoperóxido Sintasas/biosíntesis , Prostaglandina-Endoperóxido Sintasas/genética , Prostaglandina-Endoperóxido Sintasas/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-akt , Receptor ErbB-2/biosíntesis , Receptor ErbB-2/genética , Receptor ErbB-2/fisiología , Receptores de Estrógenos/biosíntesis , Transducción de Señal/fisiología , Proteínas ras/genéticaRESUMEN
Increased expression of protease-activated receptor 1 (PAR1), a G protein-coupled receptor for thrombin, has previously been correlated with breast carcinoma cell invasion. PAR1 is irreversibly proteolytically activated, internalized, and sorted directly to lysosomes, a critical process for the termination of signaling. We determined that activated PAR1 trafficking is severely altered in metastatic breast carcinoma cells but not in nonmetastatic or normal breast epithelial cells. Consequently, the proteolytically activated receptor is not sorted to lysosomes and degraded. Altered trafficking of proteolytically activated PAR1 caused sustained activation of phosphoinositide hydrolysis and extracellular signal-regulated kinase signaling, even after thrombin withdrawal, and enhanced cellular invasion. Thus, our results reveal that a novel alteration in trafficking of activated PAR1 causes persistent signaling and, in addition to other processes and proteins, contributes to breast carcinoma cell invasion.
