Substance immunologically cross-reactive with insulin from murine myeloid leukemia: purification and characterization

A substance immunologically cross-reactive with insulin (SICRI) appears in murine myeloid leukemia. Progression of disease is paralleled by the increase of SICRI levels in the serum; this increase of SICRI levels did not correlate with a decreased concentration of circulating glucose. SICRI was isolated and purified from spleen infiltrated with leukemic cells. Monospecific antiinsulin immunoglobulin G was used for immunoaffinity chromatography to isolate SICRI from tumor tissue. The purified substance yielded a single band with a molecular mass of about 150 kDa in polyacrylamide gel electrophoresis under denaturating and non-denaturating conditions. Purified SICRI enhanced growth of myeloid leukemia cells in soft agar. Biochemical and biological data together with our previous results obtained in other experimental tumors provide evidence that SICRI and insulin are two distinct biologically active agents. SICRI plays a role in murine myeloid leukemia as an autocrine growth promoting factor.