PRRG4 and breast carcinoma: PRRG4 knockdown leads to a prominent decrease in the mtDNA content in breast cancer cells, which likely contributes to the decrease in mRNA levels of the 13 mtDNA protein-encoding genes (Fig. 1D and E) and impaired mitochondrial functions (Figs. 2C and 4D) in PRRG4 knockdown cells.