CLONING AND EXPRESSION OF UNIQUE MURINE MACROPHAGE-COLONY-STIMULATINGFACTOR TRANSCRIPTS

Cocultivation of cells from the gamma-irradiated D2XRII murine bone ma rrow stromal cell line with an interleukin-3/granulocyte-macrophage co lony-stimulating factor (GM-CSF)-dependent hematopoietic progenitor ce ll line FDC-P1JL26 stimulates the emergence of factor-independent hema topoietic cell sublines. Several lines of evidence suggested that M-CS F or a protein antigenically related to M-CSF, termed leukemogenic str omal factor (LSF), that was expressed by D2XRII cells may have played a role in the emergence of the factor-independent sublines. In an effo rt to isolate a factor antigenically related to M-CSF, molecular clone s were isolated from a D2XRII cDNA library that hybridized to a mouse M-CSF genetic probe. Two of these molecular clones, designated 60.8.2 and 6452, contained an 885-bp deletion in the M-CSF coding region. Suc h a cDNA clone has not been previously described in the mouse, but a c DNA clone homologous to it has been isolated from a human pancreatic t umor cell line, MIA-PaCa-2. Three transcripts (4.8, 3.4 and 1.8 kb) we re detected that hybridized to an oligonucleotide probe that was speci fic to RNA transcripts containing the 60.8.2 deletion. The level of th e 1.8-kb transcript was not detectably induced by ionizing irradiation ; however, the levels of the 4.8-kb and 3.4-kb transcripts and two oth er M-CSF transcripts of sizes to 4.4 kb and 2.3 kb showed a 1.4- to 2. 2-fold increase after gamma irradiation. Reverse transcription-polymer ase chain reaction showed that the deletion-specific transcript(s) was detected in multiple mouse bone marrow stromal cell lines and in norm al mouse tissues. The present studies establish the existence of an in creased spectrum of murine M-CSF transcripts in bone marrow stromal ce lls and other tissues. This complexity of transcripts along with their increased accumulation after irradiation provides additional evidence for a role of proteins encoded by M-CSF transcripts in the response o f bone marrow stromal cells to ionizing irradiation. (C) 1995 by The A merican Society of Hematology.