MODULATION OF THE CYTOSKELETON AND INTRACELLULAR CALCIUM IN LEUKOCYTES EXHIBITING A CANCER-ASSOCIATED CHEMOTAXIS DEFECT

Monocyte chemotaxis is severely depressed in patients with advanced tu mors, but the cellular basis for this chemotactic defect is not known. Because the actomyosin cytoskeleton is thought to play a primary role in chemotaxis, we have employed flow cytometry to examine several asp ects of the contractile machinery including myosin II, myosin light ch ain kinase (MLCK), actin, and cytoplasmic calcium in unstimulated and in formylpeptide-stimulated neutrophils and monocytes. Serum-pretreate d polymorphonuclear leukocytes (PMNs) and monocytes from healthy blood donors or PMNs and monocytes isolated from tumor patients were studie d. Leukocytes pretreated with serum from cancer patients exhibited dec reased baseline myosin staining and a vastly different response to for mylpeptide stimulation compared with leukocytes pretreated with normal human serum. In contrast, similar amounts of MLCK were observed in ne utrophils and monocytes preincubated with normal or cancer serum with or without stimulation with formylpeptide. The fluorescent calcium ind icator fluo-3 showed that resting and fMLP-stimulated levels of intrac ellular calcium were not significantly different in control and cancer serum-pretreated human leukocytes or in leukocytes isolated from tumo r patients. Similarly, resting and fMLP-stimulated levels of F-actin i n cancer patients' leukocytes as assessed by NBD-phallacidin staining did not differ significantly from those of normal leukocytes. Because the actomyosin cytoskeleton is intricately involved in leukocyte chemo taxis, alterations in the cytoskeleton may dramatically affect cell mo tility. The cytoskeletal alterations and changes in the response of le ukocytes pretreated with cancer patients' serum to formylpeptide stimu lation as described here may result in decreased chemotaxis by these c ells.