BACKGROUND: The role of low affinity platelet factor 4 (LAPF4) in the hemopoietic microenvironment has not yet been clarified. METHODS: Low affinity platelet factor 4 (LAPF4) was purified from normal human platelets and the culture medium of the human megakaryoblastic cell line (MEG-01), and their effects upon the growth of human bone marrow fibroblasts were assessed in order to investigate the biological role of LAPF4. The purified LAPF4 was added to the culture media of human bone marrow fibroblasts up to the concentration of 200 ng/m1, and the growth rate of fibroblasts and the uptake of 3H-thymidine into fibroblasts were measured. RESULTS: The molecular weight of LAPF4 from MEG-01 was approximately 8,800, which corresponded to the monomer type of LAPF4 from normal platelets. The density of fibroblasts after 10 days of culture was 4.6 +/- 0.9 x 10(5)/ml, 7.8 +/- 0.8 x 10(5)/ml and 11.3 +/- 0.6 x 10(5) in control medium, in the medium with LAPF4 from platelets and in the medium with LAPF4 from MEG-01, respectively, which indicates that LAPF4 from MEG-01 enhanced the growth rate of bone marrow fibroblast almost 2.5 times. The uptake of 3H-thymidine into fibroblasts was significantly increased by 1,000 ng/ml of LAPF4 from MEG-01. CONCLUSIONS: These results suggest that LAPF4 may play a role in the proliferation of fibroblasts.
BACKGROUND: The role of low affinity platelet factor 4 (LAPF4) in the hemopoietic microenvironment has not yet been clarified. METHODS: Low affinity platelet factor 4 (LAPF4) was purified from normal human platelets and the culture medium of the human megakaryoblastic cell line (MEG-01), and their effects upon the growth of human bone marrow fibroblasts were assessed in order to investigate the biological role of LAPF4. The purified LAPF4 was added to the culture media of human bone marrow fibroblasts up to the concentration of 200 ng/m1, and the growth rate of fibroblasts and the uptake of 3H-thymidine into fibroblasts were measured. RESULTS: The molecular weight of LAPF4 from MEG-01 was approximately 8,800, which corresponded to the monomer type of LAPF4 from normal platelets. The density of fibroblasts after 10 days of culture was 4.6 +/- 0.9 x 10(5)/ml, 7.8 +/- 0.8 x 10(5)/ml and 11.3 +/- 0.6 x 10(5) in control medium, in the medium with LAPF4 from platelets and in the medium with LAPF4 from MEG-01, respectively, which indicates that LAPF4 from MEG-01 enhanced the growth rate of bone marrow fibroblast almost 2.5 times. The uptake of 3H-thymidine into fibroblasts was significantly increased by 1,000 ng/ml of LAPF4 from MEG-01. CONCLUSIONS: These results suggest that LAPF4 may play a role in the proliferation of fibroblasts.