RESUMO
LIM and SH3 protein (LASP-1), initially identified from human breast cancer, is a specific focal adhesion protein involved in cell migration. LASP-1 is an actin binding protein, which also interacts with the proline-rich domains of zyxin, a scaffolding protein required for cell movement and gene transcription. In the present work, we analyzed the effect of LASP-1 on different human breast cancer cell lines. Transfection with LASP-1-specific siRNA resulted in a reduced protein level of LASP-1 in BT-20 and MCF-7 cell lines. The siRNA-treated cells were arrested in G2/M phase of cell cycle, and proliferation of the tumor cells was suppressed by 30-50% corresponding to around 50% of the cells being transfected successfully as seen by immunofluorescence. In addition, tumor cells showed a 50% reduced migration after siRNA treatment, while overexpression of LASP-1 in non-tumor PTK-2 cells, which do not express endogenous LASP-1, resulted in a significant increase in cell motility. LASP-1 silencing is accompanied with a reduced binding of the of LASP-1 binding partner zyxin to focal contacts without changes in actin stress fiber organization as observed in immunofluorescence experiments. The data provide evidence for an essential role of LASP-1 in tumor cell growth and migration, possibly by influencing the localization of zyxin.
Assuntos
Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Movimento Celular/genética , Proliferação de Células , Inativação Gênica , Glicoproteínas/metabolismo , Inibidores do Crescimento/genética , Proteínas de Homeodomínio/genética , Proteínas de Neoplasias/genética , Proteínas Adaptadoras de Transdução de Sinal , Linhagem Celular Tumoral , Proteínas do Citoesqueleto , Regulação para Baixo/genética , Feminino , Inibidores do Crescimento/fisiologia , Proteínas de Homeodomínio/antagonistas & inibidores , Proteínas de Homeodomínio/fisiologia , Humanos , Imuno-Histoquímica , Proteínas com Domínio LIM , Proteínas de Neoplasias/antagonistas & inibidores , Proteínas de Neoplasias/fisiologia , ZixinaRESUMO
LIM and SH3 domain protein (LASP-1) is a specific focal adhesion protein involved in cell migration. Overlay studies demonstrate that LASP-1 directly binds to the proline-rich domains of zyxin, lipoma preferred partner (LPP), and vasodilator-stimulated phosphoprotein (VASP), with zyxin being the most prominent interacting partner. Despite the LIM/zinc-finger domain, hypothesized to be involved in homodimerization, LASP-1 exists as a monomer. In vitro phosphorylation of recombinant mouse LASP-1 by cAMP- and cGMP-dependent protein kinase (PKA and PKG, respectively) occurs at serine 61, serine 99, and threonine 156 whereas in intact cells mouse LASP-1 is phosphorylated only at threonine 156. This site is different from the known in vivo phosphorylation sites in human (serine 146) and rabbit (serine 99 and serine 146). Nevertheless, immunofluorescence of LASP-1 in human and mouse mesangial cells revealed no difference in subcellular distribution. Exposure of the cells to forskolin induced a translocation of both, human and mouse LASP-1, from the focal contacts to the cell interior without affecting F-actin structure. Immunoblotting of LASP-1 in various mouse and human tissues detected a similar prominent expression in non-muscle tissue. Altogether, our data suggest so far no functional differences between human and mouse LASP-1.