The role of protein kinase C in the regulation of cell growth and in signalling to the cell nucleus

The protein kinase C (PKC) family of serine/ threonine kinases consists of at least 11 mammalian isoforms, which show slight differences in their molecular structure and enzymatic properties. PKC isoforms are involved in a wide variety of intracellular signalling events and play an important role in tumour promotion and cell growth control in general. Studies of expression levels in cancer cells and studies using overexpression of single isoforms or expression of dominant negative isoforms reveal that, depending on the cellular background, PKC isoforms can either promote or inhibit cell growth. To understand the role of PKC isoforms in growth control, it is essential to understand how PKC functions in the intracellular signalling cascades towards the cell nucleus. Recent work has shown that PKC isoforms can act either in the cytoplasm, and cause nuclear effects indirectly by triggering signalling pathways directed towards the cell nucleus, or, after translocation and activation, can themselves act in the cell nucleus.