Role of Aberrant Sialylation of Chronic Myeloid Leukemia Granulocytes on Binding and Signal Transduction by Chemotactic Peptides and Colony Stimulating Factors

Abstract

Chronic myelogenous leukemia (CML) granulocytes exhibit a number of characteristics attributable to immature granulocytes, including marked increases in cell surface sialylation of glycoproteins which may be due, at least in part, to an increased activity of cytidine 5 ‘-monophosphate-N-acetylneuraminic acid: Ga1 βl -3Gal NAcα(2–3)-sialytransferase (EC 2.4.99.4), and perhaps to altered activity of other glycosyltransferases and sialidases. This aberrant sialylation of CML granulocytes contributes to the decreased binding of the synthetic chemotactic peptide, formyl Met Leu Phe (fMLP), to the surface of CML granulocytes which leads to a rapid, transient increase in cytosolic free calcium ([Ca²⁺]₁), an integral step in the biochemical cascade leading to cell activation. To determine if the decrease in binding of fMLP to CML granulocytes translates into a functional deficit, we measured fMLP-induced increases in [Ca²⁺]₁. Compared to normal granulocytes, fMLP-induced increases in [Ca²⁺]_i were markedly decreased in CML granulocytes. After sialidase treatment, a significant augmentation in fMLP-induced increases in [Ca²⁺]_i was noted in CML granulocytes, indicating that the decreased signalling may be a consequence of aberrant sialylation. To determine if the effects of aberrant sialylation also alters the binding of endogenous polypeptide mediators, we determined the effect of desialylation of CML and normal granulocytes on binding of the colony stimulating factor for granulocytes and monocytes (GM-CSF), which plays a role in differentiation and proliferation of myeloid-lineage cells. As with fMLP binding, we also showed that the binding of GM-CSF to CML granulocytes, but not normal granulocytes, was markedly increased after sialidase treatment. Similarly, binding of GM-CSF to undifferen-tiated HL-60 cells was markedly increased after sialidase treatment. Therefore, we have demonstrated that aberrant sialylation of CML granulocytes not only alters the binding of fMLP and GM-CSF to their receptor(s), but may also alter signal transduction. Thus, aberrant gly-cosylation of CML granulocytes may reduce the binding of hematopoietic growth factors, which in turn may be responsible for the immature phenotype of CML granulocytes.

Key Words:

• Aberrant sialylation
• CML granulocytes
• signal transduction
• chemotactic peptides colony stimulating factors