Effects of CRF on 4T1 cells proliferation. 4T1 cells were treated with different doses of CRF for 48 to 96 hours. CRF significantly induced proliferation of 4T1 cells, as measured by the MTT assay. The CRF1 antagonist Antalarmin reversed this effect. Data are expressed as the MEAN ± SEM of three independent experiments. * p < 0.05 compared to untreated control cells, + p < 0.05 compared to cells treated with 10-8M CRF and # p < 0.05 compared to cells treated with 10-9M CRF.