[Relationship between protein tyrosine phosphorylation level and anoikis resistance of breast tumor cell lines]

Normal epithelial or endothelial cells can undergo anoikis, a type of apoptosis, when they are detached from their extracellular matrices (ECM), while most tumor cells derived from epithelial or endothelial tissues lose this feature. Most of the studies indicate that anoikis resistance of tumor cells is closely related to abnormal signal transductioin. The aim of this research was to screen out the tumor cell lines that are anoikis resistant, then to investigate the relationship between the protein tyrosine phosphorylation of signaling molecules and anoikis resistance feature of tumor cells.

Anoikis resistance of breast tumor cell lines MCF-7, Bcap-37, and MDA-MB-231 was determined by DNA ladder assay, flow cytometry analysis, and soft agar assay upon suspending culture. A normal epithelial cell line MDCK (Madin-Darby canine kidney) was taken as a control. The inhibitory effect of genistein, a general protein tyrosine kinase inhibitor, on anoikis resistance of tumor cells was analyzed at the same time. The differences of total protein tyrosine phosphorylation levels between suspended and attached cultural conditions of three breast cancer cell lines were examined by Western blot analysis.

All the three tumor cell lines were distinctly anoikis resistant. Further study showed that these features could be suppressed by genistein. The results of Western blot analysis showed that the general level of tyrosine phosphorylation in suspended MDCK cells was decreased compared with that in attached cells, while tyrosine phosphorylation level of some proteins increased (more than 3.5-6.5 folds) aberrantly in suspended tumor cells.

All the three breast tumor cells in this study are anoikis resistant respectively to some extent, and aberrant tyrosine phosphorylation of signaling proteins may play a role in the process of anoikis resistance of these tumor cells.