Use of protein (serine/threonine) kinase activators and inhibitors to study protein phosphorylation in intact cells

Abstract A complete understanding of the organization and functioning of a protein phosphorylation system requires the co-operation of several different approaches, such as molecular pharmacology, genetic manipulation, bio¬ chemistry, and cell biology. The advent of a new class of effective pharmacological agents is always an event of considerable interest, in particular for new types of antagonists, i.e. potentially important groups of compounds that act by specifically blocking one or more of the steps in intracellular signalling systems (1). There is now convincing evidence that intracellular protein phosphorylation systems are common mechanisms of fundamental importance in biological regulation. A large number of cellular mechanisms involving protein phosphorylation have been revealed over the past decade. However, interrelationships among each signal cascade are complex and uncertainties concerning the cellular responses in these systems remain. In order to better understand these events, improved and sophisticated methods for estimating changes in the activities of cellular response elements after extracellular stimulation have to be designed. While the biochemistry and molecular biology of protein kinases has progressed, it has been much more difficult to understand their function in intact cells. For this reason researchers studying second messenger systems and protein phosphorylation have long sought the development of specific and effective inhibitors that would permit the definitive determination of the physiological role of the protein kinases (2). Protein kinase inhibitors can be used to determine the physiological role of protein phosphorylation systems in various types of cells.