SMAD1 and cancer: PDK4 is reported to bind CREB in the cytoplasm, prevent its degradation and activate the mTORC1 signalling pathway in cancer cells.34 Moreover, PDK4 enhances vascular calcification via SMAD1/5/8 phosphorylation in both the cytoplasm and mitochondria.37 To clarify the mechanistic pathways by which PDK4 regulates ovarian CSCs, lysates were screened from ALDH+CD44+ SKOV3 cells treated with or without siPDK4 for the phosphokinase array.