Multiple subcellular localizations and functions of protein kinase C delta in liver cancer

Protein kinase C delta (PKC delta) is a member of the PKC family, and its implications have been reported in various biological and cancerous processes, including cell proliferation, cell death, tumor suppression, and tumor progression. In liver cancer cells, accumulating reports show the bi-functional regulation of PKC delta in cell death and survival. PKC delta function is defined by various factors, such as phosphorylation, catalytic domain cleavage, and subcellular localization. PKC delta has multiple intracellular distribution patterns, ranging from the cytosol to the nucleus. We recently found a unique extracellular localization of PKC delta in liver cancer and its growth factor-like function in liver cancer cells. In this review, we first discuss the structural features of PKC delta and then focus on the functional diversity of PKC delta based on its subcellular localization, such as the nucleus, cell surface, and extracellular space. These findings improve our knowledge of PKC delta involvement in the progression of liver cancer.