Towards capturing an atomic view of the activation of P-Rex oncogenes at the membrane

Lucato CM1, Mitchell CA1, Whisstock JC1, Halls ML2 and Ellisdon AM1

  1. Biomedicine Discovery Institute, Monash University.
  2. Monash Institute of Pharmaceutical Sciences, Monash University.

P-Rex1 and 2 are guanine nucleotide exchange factors that activate a number of Rho family GTPases that are crucial in regulating cell growth and motility. Interestingly, P-Rex proteins regulate these cellular functions downstream of a number of GPCRs and RTKs and, in doing so, function as a membrane-localised signalling node in many cancer-associated pathways. Recently, P-Rex1 expression was shown to be necessary for melanoma dissemination and has been associated with increased metastatic phenotypes in both breast and prostate cancer. P-Rex1 is therefore a critical signal integrator in tumorigenesis and metastasis and subsequently a desirable therapeutic target, however currently there is little mechanistic understanding of its mode of activity. Crystallization and structural analysis of the catalytic DH-PH domains of P-Rex1 have allowed the elucidation of its mechanism of nucleotide exchange. This exchange activity is inhibited by interactions with P-Rex1 C-terminal domains which have been mapped with cross-linking and mass spectrometry. Interestingly, intra-domain cross-links move significantly upon effector binding and analysis of these movements has allowed for characterization of the multi-step P-Rex1 activation pathway. Further, molecular differences between autoinhibited P-Rex1 (185kDa) and effector-bound, partially activated P-Rex1 complexes (~230kDa) have been visualized with cryo-electron microscopy and resulting models have provided further molecular insight into the mode of P-Rex1 activation.