EFFECTS OF GAMMA-IRRADIATION ON THE M-CSF-PROMOTER LINKED TO A CHLORAMPHENICOL AMINOACYL TRANSFERASE REPORTER GENE EXPRESSED IN A CLONAL MURINE BONE-MARROW STROMAL CELL-LINE

The effects of cytokines produced by bone marrow stromal cells on clos ely associated hematopoietic cells constitute a major component of the physiology of the hematopoietic microenvironment. A major cytokine pr oduced by marrow stromal cells is macrophage colony-stimulating factor (M-CSF). To determine the effect of gamma-irradiation on the M-CSF pr omoter in bone marrow stromal cells, we selected a clonal cell line fr om the C3H/HeJ mouse marrow stromal cell line D2XRII and stably transf ected a reporter construct containing the murine M-CSF-promoter linked to a chloramphenicol aminoacyl transferase (CAT) gene. CAT activity w as measured at serial time points after gamma-irradiation in vitro to doses between 500 and 10,000 cGy at a dose rate of 116 cGy/min. D2XRII marrow stromal cells treated with phorbol myristate acetate (40 mu g/ ml, four h), demonstrated a significant two-fold increase in CAT activ ity. In contrast, CAT activity measured immediately, 24 h, 72 h or 1 w eek after gamma-irradiation, showed no significant increase or decreas e in CAT activity. An increase in CAT activity was detected 48 h after irradiation with cells that received 5,000 cGy. Thus, single fraction gamma-irradiation of plateau phase bone marrow stromal cells did not decrease M-CSF-promoter activity. These results are consistent with pr ior experimental data demonstrating stable levels of release of M-CSF protein following gamma-irradiation of bone marrow stromal cells and i mply that the stability of transcription of the gene for this importan t cytokine is protected from irradiation.