Klein, C. H. | Search bioRxiv

bioRxiv2018

A spatially regulated GTPase cycle of Rheb controls growth factor signaling to mTORC1

Growth factors initiate anabolism by activating mechanistic target of rapamycin complex 1 (mTORC1) via the small GTPase Rheb. We show that the GTPase cycle of Rheb is spatially regulated by the interaction with its GDI-like solubilizing factor (GSF) - PDE{delta}. Arl2-GTP mediated localized release of cytosolic Rheb-GTP from PDE{delta} deposits it onto perinuclear membranes where it forms a complex with mTORC1. The membrane associated GTPase activating protein (GAP) TSC2 hydrolyzes Rheb-GTP, weakening the interaction with mTOR. Rheb-GDP is readily released into the cytosol where it is maintained soluble by interaction with PDE{delta}. This solubilized Rheb is re-activated by nucleotide exchange to be re-deposited by Arl2-mediated release onto perinuclear membranes. This spatial GTPase cycle thereby enables mTORC1 activation to be solely controlled by growth factor induced inactivation of TSC2. The coupling between mTOR activation and spatially regulated Rheb nucleotide exchange makes growth factor induced proliferation critically dependent on PDE{delta} expression.

cell biology↗

bioRxiv2018

PDEδ inhibition impedes the proliferation and survival of human colorectal cancer cell lines harboring oncogenic KRas

Novelty and ImpactThe undruggable KRas is a prevalent oncogene in CRC with poor prognosis. In hPDAC cells pharmacological targeting of PDE{delta} affects oncogenic KRas signaling, but it remained unclear whether this approach is transferable to other cancer cells. Here, we show that genetic and pharmacologic PDE{delta} inhibition also impedes the proliferation of oncogenic, but not wild-type KRas bearing CRC cells indicating that PDE{delta} inhibition is a specific tool for targeting growth of oncogenic KRas bearing CRC.\n\nAbstractRas proteins, most notably KRas, are prevalent oncogenes in human cancer. Plasma membrane localization and thereby signaling of KRas is regulated by the prenyl-binding protein PDE{delta}. Recently, we have reported the specific anti-proliferative effects of PDE{delta} inhibition in KRas-dependent human pancreatic ductal adenocarcinoma cell lines. Here, we investigated the proliferative dependence on the solubilizing activity of PDE{delta} of human colorectal cancer (CRC) cell lines with or without oncogenic KRas mutations. Our results show that genetic and pharmacologic interference with PDE{delta} specifically inhibits proliferation and survival of CRC cell lines harboring oncogenic KRas mutations whereas isogenic cell lines in which the KRas oncogene has been removed, or cell lines with oncogenic BRaf mutations or EGFR overexpression are not dependent on PDE{delta}. Pharmacological PDE{delta} inhibition is therefore a possible new avenue to target oncogenic KRas bearing CRC.

cell biology↗