The effect of cytosine-arabinoside treatment on the overexpression of c-myc protooncogene in a case of prolymphocytic leukemia

An unusually high level of expression of the c-myc protooncogene was observed in peripheral blood lymphocytes of a patient with prolymphocytic leukemia (atypical chronic lymphocytic leukemia). The overexpression of c-myc could not be attributed to a high level of proliferating activity of the leukemic cells in the blood. Treatment with cytosine-arabinoside at high doses abolished this altered expression of c-myc and resulted in a twofold increase in the expression of a gene sequence encoding the invariant γ-chain of class II histocompatibility antigens, preferentially expressed in resting B lymphocytes. These observations suggest that the leukemic cells may have been arrested in the cell cycle outside the G₀ phase. Our findings demonstrate that growth-regulated genes can be useful molecular markers of diseases with altered mechanisms of cellular proliferation.