SLC25A33 and breast cancer: In cultured MCF‐7 (a human breast cancer cell line) and HeLa cells (a human cervical cancer cell line), IGF‐1 signaling was shown to promote the expression of pyrimidine nucleotide carrier 1 (PNC1), a protein that carries deoxynucleotides, that is, the precursors for mtDNA synthesis, from the cytoplasm into mitochondria; in turn, PNC1 was observed to regulate the duplication of mtDNA and its transcription, mitochondrial ROS, and energy production, as well as the capacity of cancer cells to acquire invasive characteristics (Favre et al., 2010).