The molecular model of PKC life cycle explained through Systems Biology Approach

Protein kinase C (PKC) is a family of kinases which is poised to transduce signals emanating from the cell surface. Membranes of most cells provide the regulatory platform for supporting the life cycle and function of PKC enzymes. Maturation, activation and termination are three key regulatory steps of PKC life cycle. These regulatory steps precisely control the level of signaling competent PKC enzyme in the cells and any dysfunction in this regulation results in pathophysiological disease state such as cancer, where PKC levels are observed to be altered. Here, we describe a molecular model of PKC life cycle based on computational approach. Our model explains the fate of PKC during denovo synthesis and lipid mediated activation cycle. Through our systems biology approach we show that life cycle of PKC is controlled by multiple phosphorylation and dephosphorylation events. PKC processing events can be divided into two types 1: Maturation processing of newly synthesized enzyme; 2. Activation of enzyme. Newly synthesized PKC enzyme is constitutively processed through three ordered phosphorylations and is stored in cytosol as a signaling competent inactive molecule. First step in this maturation sequence of PKC is PDK 1 mediated phosphorylation at activation loop (Thr 500 in PKCβII). Once phosphorylated at activation loop PKC molecule binds with mTORC 2 complex and undergoes constitutive auto‐phosphorylations at turn and hydrophobic motifs (Thr 641 and Ser 660 in PKCβII). Upon stimulation by extra‐cellular stimuli the generation of diacylglycerol (DAG) and Ca +2 at membrane engages the PKC molecule through binding at C 2 and C 1 domains respectively. This activates the enzyme. Our model explains all these steps in PKC lifecycle through a quantitative approach. Our model also shows that once active PKC molecule is prone to de‐phosphorylation (PHLPP‐mediated) and degradation. This model also explains the stabilizing role of HSP‐60 in rescuing the de‐phosphorylated molecule and assisting its re‐phosphorylation, thus re‐building the pool of signaling competent enzyme after activation cycle. This model shows that for small to moderate activation stimuli the pool of PKC molecule is effectively unchanged however, larger stimuli can down‐regulate the enzyme through degradation pathways. Our results also show that blocking the PHLPP de‐phosphorylation pathway could recover the PKC pool in a dose dependent manner even after a large amplitude stimulus has been applied. Our results also points toward a possible role of HSP‐60 overexpression in recovering the PKC signaling competent pool after large amplitude stimuli has been applied. The results presented in this communication unravel some interesting aspects of PKC life cycle through a computational approach. Enhancing the understanding of PKC life cycle could be instrumental in translating new drugs for this important transducing molecule for diseases like breast cancer. Support or Funding Information BioSystOmics