RESUMEN
The PAK2/ßPIX/GIT1 (p21-activated kinase 2/PAK-interacting exchange factor-ß/G protein-coupled receptor kinase-interactor 1) complex has been shown to distribute to both membrane ruffles and focal adhesions of cells, where it plays an important role in regulating focal adhesion turnover. However, the detailed mechanism underlying this regulation is largely unknown. We previously reported that MYO18Aα interacts via its carboxyl terminus with the PAK2/ßPIX/GIT1 complex through direct binding to ßPIX, and that knockdown of MYO18Aα in epithelial cells causes accumulation of the complex in focal adhesions and decreased cell migration ability (Hsu et al., 2010). The current study characterized the detailed MYO18Aα-ßPIX interaction mechanism and the biological significance of this interaction. We found that deletion of the carboxyl-terminal globular domain of MYO18Aα profoundly altered the cellular localization of ßPIX and inhibited cell migration. ßPIX interacts through its most carboxyl-terminus, PAWDETNL (639-646), with MYO18Aα and partially colocalized with MYO18Aα in membrane ruffles of cells, whereas ßPIX(1-638), a mutant with deletion of PAWDETNL, accumulated in focal adhesions. Both focal adhesion numbers and area in ßPIX(1-638)-expressing cells were greater than those in cells expressing wild-type ßPIX(FL). Further experiments using deletion mutants of MYO18A and ßPIX showed that disruption of MYO18A-ßPIX interaction not only impaired cell motility but also decreased Rac1 activity. Collectively, our data unravel the interaction regions between MYO18A and ßPIX and provide evidence for the critical role of this interaction in regulating cellular localization of ßPIX, Rac1 activity, and adhesion and migration in epithelial cells.
RESUMEN
BACKGROUND: The cancer cell secretome has been recognized as a valuable reservoir for identifying novel serum/plasma biomarkers for different cancers, including colorectal cancer (CRC). This study aimed to verify four CRC cell-secreted proteins (tumor-associated calcium signal transducer 2/trophoblast cell surface antigen 2 (TACSTD2/TROP2), tetraspanin-6 (TSPAN6), bone marrow stromal antigen 2 (BST2), and tumor necrosis factor receptor superfamily member 16 (NGFR)) as potential plasma CRC biomarkers. METHODS: The study population comprises 152 CRC patients and 152 controls. Target protein levels in plasma and tissue samples were assessed by ELISA and immunohistochemistry, respectively. RESULTS: Among the four candidate proteins examined by ELISA in a small sample set, only BST2 showed significantly elevated plasma levels in CRC patients versus controls. Immunohistochemical analysis revealed the overexpression of BST2 in CRC tissues, and higher BST2 expression levels correlated with poorer 5-year survival (46.47% versus 65.57%; p = 0.044). Further verification confirmed the elevated plasma BST2 levels in CRC patients (2.35 ± 0.13 ng/mL) versus controls (1.04 ± 0.03 ng/mL) (p < 0.01), with an area under the ROC curve (AUC) being 0.858 comparable to that of CEA (0.867). CONCLUSION: BST2, a membrane protein selectively detected in CRC cell secretome, may be a novel plasma biomarker and prognosticator for CRC.