The F-actin content of multiple myeloma cells as a measure of their migration.

One of the main characteristics of multiple myeloma (MM) cells is their specific homing and growth in the bone marrow (BM). For their homing, MM cells need chemotactic signals to be attracted towards the BM and to be activated. Profound knowledge of the different chemokines for MM cells and their signal transduction pathways is necessary to interfere in this process. We studied here an extra possible tool for the investigation of the different chemokines and their pathways. The 5T experimental mouse model was used to investigate the migration of MM cells towards BM stromal cells. We studied the changes of the F-actin content in the 5TMM cells in the presence of BM stromal cell conditioned medium and we correlated this with their migratory capacity. F-actin became polarized when the cells were migrating, in contrast to nonmigrating cells. This polarization could not only be seen by fluorescence and confocal laser scanning microscopy, but also could be quantified by fluorometry and flow cytometry. The correlation between the F-actin content of the MM cells and their migration capacity thus makes its quantification a useful tool in studying their migratory behavior.