Nuclear AP-1-Fra-1/c-Fos and cytoplasmic Fra-1/c-Fos are required at early and late stages of cell proliferation, respectively.

<p>(<b>A</b>) MDA-MB231 cells were cultured+or – NLSP that blocks AP-1 nuclear import, in the presence or the absence of anti-Fra-1 or anti-c-Fos antibodies added at the indicated times (0 h or 16 h) after FBS addition and examined for proliferation. Controls were performed that received FITC-IgG antibody (last column). Proliferation was determined as indicated under <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053211#s2" target="_blank">Materials and Methods</a> and expressed as arbitrary fluorescent units of DNA. Results are the mean ± SD of 3 experiments performed in quintuplicate; 10,000 cells were plated for each proliferation assay. Note that nuclear import of Fra-1/c-Fos-AP-1 is required only during the first 16 h after FBS addition whereas cytoplasmic Fra-1/c-Fos are required at all time points (compare column 5 with columns 6,7 or 8). (<b>B</b>) TH form MDA-MB231 cells cultured as in (A) were assayed for phospholipid synthesis capacity. Results are the mean cpm incorporated into phospholipids/mg protein ± SD of 3 experiments performed in triplicate. *: p<0.001.