UNDERSTANDING PROTEIN KINASE PDK1 REGULATION USING SMALL MOLECULES TARGETING DIFFERENT SITES

SACERDOTI, MARIANA; FROESE, KARIN; SCHULZE, JÖRG; PASTOR-FLORES, DANIEL; BAUER, ANGELIKA; HERBRAND, AMANDA; RILEY, ANDREW; CZIER, GYLES; POTTER, BARRY; SUESS, EVELYN; GROSS, LISSY; LEROUX, ALEJANDRO E.; BIONDI, RICARDO M.

Salta

Congreso; LV Reunión Científica anual SAIB y XIV congreso de PABMB; 2019

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Overactivation of thephosphoinositide 3-kinase (PI3K) pathway is one of the most frequent events incancer, a disease that is becoming increasingly frequent because of theincrease in life expectancy. A key PI3K downstream event is the phosphorylationof PKB/Akt, S6K, SGK and RSK by master kinase phosphoinositide-dependentprotein kinase-1 (PDK1), which also phosphorylates other protein kinasesconstitutively. Throughout the years we have investigated different mechanismsused by PDK1 to specifically and timely phosphorylate its substrates.Phosphorylation of most substrates, like S6K, SGK, PKC, PRK/PKN, relies on adocking interaction where a C-terminal hydrophobic motif (HM) interacts with aregulatory site, PIF-pocket, located on the small lobe of the kinase domain ofPDK1. Since some substrates interact better with PDK1 when their HM isphosphorylated, this acts as a regulated docking interaction. In addition, theinteraction with the PIF-pocket allosterically ?activates? PDK1 itself,stabilizing a closed-active structure of the catalytic domain. We havedescribed in the past that the binding of the HM or small compounds to thePIF-pocket allosterically affects the ATP-binding site. Allosteryimplies that the reverse modulation, i.e. from the ATP-binding site to theregulatory PIF-pocket, should also be possible. Indeed, we have shown thatsmall molecules and metabolites binding at the ATP-binding site can inhibit orenhance the docking interaction at the PIF-pocket. This is important for themechanism of action of drugs. Interestingly, the interaction with thePIF-pocket of PDK1 is not a requirement for the phosphorylation of PKB/Aktafter PI3K activation. Although the HM of PKB/Akt does interact with thePIF-pocket of PDK1, we believe that other mechanisms must regulate thatinteraction. PDK1 has been described to dimerize. We will here providepreliminary data and discuss if dimerization could also be part of themechanism by which PDK1 phosphorylates its substrates. We describe the effectof different inositol poliphosphorylated molecules and present results of ascreening performed in order to find small compounds to regulate dimerformation.