MURINE SARCOMA-VIRUSES BLOCK CORTICOSTEROID-INDUCED DIFFERENTIATION OF BONE-MARROW PREADIPOCYTES ASSOCIATED WITH LONG-TERM INVITRO HEMATOPOIESIS

A unique population of clonagenic bone marrow cells accumulates neutral fat and differentiates to adipocyte morphology in response to 10-7 M 17-hydroxy-corticosteroid. Differentiation of these adherent marrow preadipocytes is associated with maintenance of pluripotent hemopoietic stem cell and granulocyte-macrophage progenitor cell proliferation in bone marrow cultures in vitro. The present studies demonstrate that infection of preadipocytes with Harvey, Kirsten, or Moloney strains of murine sarcoma virus (MSV) but not the associated helper leukemia virus blocks corticosteroid-induced lipogenesis. This effect is observed both in whole marrow culture and in a new assay for the individual colony-forming unit adipocyte (CFUa). CFUa are single cells concentrated in light density fractions of an isopycnic density gradient, normally accumulate lipid, and grow to ≥50 cell colonies following suspension in 0.8% methylcellulose-containing medium with horse serum and hydrocortisone. An MSV-specific block of both CFUa formation and insulin-dependent differentiation of the 3T3-L1 embryo preadipocyte cell line is detected by 14 days. In contrast, MSV infection of granulocyte-macrophage progenitor cells in the same marrow does not block differentiation in response to colony-stimulating factor. These data indicate that cells of a specific phenotype can be identified within an organ culture as targets for the early biological effects of a particular class of RNA type-C viruses. © 1979.