Fig. 7

PRRG4 promotes migration and invasion of breast cancer cells through the STAT3-POLG axis. A STAT3 inhibitor decreased the filopodia formation enhanced by PRRG4 overexpression. Serum-starved cells seeded on cover slips were incubated with vehicle or 4 µM Stattic for 11 h, and stimulated with 10% FBS for 1 h in the presence of vehicle or 4 µM Stattic. Cells (MDA-MB-231 cells, left image panel; HCC1954 cells, right image panel) were fixed and stained with Actin-Tracker Green. Five micrographs/cell line were used to quantitate filopodia numbers. Scale bars, 25 μm (upper image panels), and 5 μm (lower image panels). B and C PRRG4 overexpression promotes migration and invasion of breast cancer cells through STAT3 and LPSY189 motif. Indicated cells were treated with vehicle or Stattic (3 µM for MDA-MB-231 and 2 µM for HCC1954) for 20 h. D Generation of cells with both POLG overexpression and PRRG4 knockdown. SUM149PT cells were infected with pBabe-Hygro vector alone and pBabe-Hygro POLG retroviruses, and selected with hygromycin before being infected with PLKO.1 lentiviruses expressing control-shRNA and two different PRRG4-shRNAs respectively. Cells were immunoblotted with the indicated antibodies. POLG levels were quantified and normalized to corresponding β-actin levels, which were presented as fold changes relative to control that was set to 1. E Overexpression of POLG increases mtDNA content and prevents the decrease in mtDNA content induced by PRRG4 knockdown. F Overexpression of POLG increases the basal (Base) and oligomycin-sensitive (Oligo-sensitive) ATP contents and prevents the decrease in the basal and oligomycin-sensitive ATP contents induced by PRRG4 knockdown. G and H POLG overexpression enhances cell migration and invasion, and prevents the decrease in cell migration and invasion induced by PRRG4 knockdown in SUM149PT cells. Scale bars, 50 μm *p < 0.05, **p < 0.01, ***p < 0.001