To examine whether MAPK4 plays a major role in regulating PDK1 protein stability, we first examined PDK1 protein stability in 7 TNBC cancer cell lines, including the MAPK4-low HCC1806, MDA-MB-468, HCC1395 cells, and the MAPK4-medium/high SUM159, MDA-MB-231, HCC1937, and HS578T cell lines. Here, MAPK4 is linked to cancer.