Effects of Integrin α₅β₁-Mediated Signal TransductionPathways on the Proliferation and Apoptosis of K562 and CML Cells.

Objective and methods: More than 90% of chronic myeloid leukemia (CML) patients have the Philadelphia (Ph) chromosome which produces a specific oncoprotein known as BCR/ABL (P210 protein). Having strong tyrosine kinase activity, the BCR/ABL oncoprotein can trigger several signal transduction pathways and inhibit the normal signal transduction pathways of CML progenitor cells. Presenting on cell surface, Integrins belong to the adhesive molecule family. They mediate adhesion of cell to cell or cell to extra cellular matrix (ECM) and take part in many physiological and pathological processes such as signaling transduction, cell differentiation, proliferation and apoptosis. Many studies showed that abnormal circulating of CML Ph⁺ cells in peripheral blood and unregulated proliferation of CML Ph⁺ cells in bone marrow were related closely to the abnormal adhesion function of integrins. It is also well known that Interferon (IFN)-α is one of the effective therapeutic agents for CML. Therefore the present study was designed, by cell culture, FCM, RT-PCR and Western Blot, to observe the effects of IFNα-2b on the proliferation of k562 cells and fresh leukemia cells from patients with CML-in blast crisis (CML cells), before and after integrin α5β1 having been neutralized by Anti-integrin α5β1 monoclonal antibody (Anti-α5β1), and to investigate the changes of mRNA and protein of several key molecules in integrin-mediated pathways, such as FAK, ERK, AKT, PI3K and Cychin D1, p21 and survivin before and after the treatment of Anti-α5β1 with or without IFNα-2b.

Results: The expression level of integrin α5β1 on K562 cells and CML cells was much higher than that on health volunteers’ BMMNC. And the adhesion capability of K562 cells and CML cells to fibronectin (FN) decreased significantly than that of health volunteers’ BMMNC. IFNα-2b improved the adhesion capability of K562 cells and CML cells to FN. Anti-α5β1 inhibited proliferation but induced apoptosis and G₀/G₁ arresting of K562 cells and CML cells. Anti-α5β1 downregulated the expression level of p-FAK-, p-ERK-, PI3K- and p-AKT-mRNA and protein. Anti-α5β1 also downregulated the expression level of Cyclin D1 mRNA, but upregulated the expression level of P21 mRNA. Moreover, the effect of Anti-α5β1 is stronger than that of IFNα-2b.

Conclusions: Anti-α5β1 inhibited integrin α5β1-mediated signal transduction pathways: FAK-ras-ERK pathway and PI3K-AKT-survivin pathway. This might be the mechanisms of Anti-α5β1 inhibiting proliferation and inducing apoptosis of K562 cellsand CML cells. This indicated that the dysfunction of integrin α5β1 pathway might have important meanings in the leukemogenesis of CML and might become a new target for the treatment of CM.