A Circuit for Secretion-coupled Cellular Autonomy in Multicellular Eukaryotes

Abstract

SUMMARYIntercellular (between-cells) signals must be converted into an intracellular (within-cell) signal before it can trigger a proportionate response. How cells mount such proportionate responses within their interior remains unknown. Here we unravel the role of a coupled GTPase circuit on the Golgi membranes which enables the intracellular secretory machinery to respond proportionately to the growth factors in the extracellular space. The circuit, comprised of two species of biological switches, the Ras-superfamily monomeric GTPase Arf1, and the heterotrimeric GTPase, Giαβγ and their corresponding GAPs and GEFs, is coupled via at least one a forward and two key negative feedback loops. Interrogation of the circuit featuring such closed-loop control (CLC) using an integrated systems-based and experimental approach showed that CLC allows the two GTPases to mutually control each other and convert the expected switch-like behavior of Arf1 into an unexpected dose response aligned (DoRA) linear behavior. Such behavior translates into growth factor stimulated Giαβγ activity on Golgi membranes, temporal finiteness of Arf1 activity, and cellular secretion that is proportional to the stimuli. Findings reveal the importance of the coupled GTPase circuit in rendering concordant cellular responses via the faithful transmission of growth signals to the secretory machinery.GRAPHIC ABSTRACTHIGHLIGHTSEndo- (mono) and ectomembrane (trimeric) GTPase systems are believed to function independently.Their coupling in a closed loop system at the Golgi makes cell secretion proportionate to stimuli.Coupling enables closed-loop mutual control of both GTPases and dose response alignment (DoRA).Uncoupling creates an open loop which generates misaligned and discordant responses.

Growth Signaling Autonomy in Circulating Tumor Cells Aids Metastatic Seeding

“…To study how autonomy in cancer cells impact cancer progression, and more specifically, breast cancers, we took the advantage of two MDA MB-231 breast cancer cell lines, that are either endowed (WT) or impaired (GIV-KO by CRISPR ( 24 )) in growth signaling autonomy ( Fig 1a ). We focused on these cells because they are a highly aggressive, invasive, and poorly differentiated triple-negative breast cancer (TNBC) cell line which lacks the estrogen receptor (ER), progesterone receptor (PR), as well as amplification of the HER2 (human epidermal growth factor receptor 2) receptor and is one of the triple-negative basal subtype cell line most widely used in metastatic breast cancer research ( 27 ) (40.2% of total PubMed citations).…”

“…We focused on these cells because they are a highly aggressive, invasive, and poorly differentiated triple-negative breast cancer (TNBC) cell line which lacks the estrogen receptor (ER), progesterone receptor (PR), as well as amplification of the HER2 (human epidermal growth factor receptor 2) receptor and is one of the triple-negative basal subtype cell line most widely used in metastatic breast cancer research ( 27 ) (40.2% of total PubMed citations). It is also a cell line that has been shown to require GIV for growth signaling autonomy ( 24 ). We analyzed these cells by functional and ‘omics’-based approaches to navigate the uncharted territory of cancer cell autonomy.…”

“…We analyzed these cells by functional and ‘omics’-based approaches to navigate the uncharted territory of cancer cell autonomy. Because the GTPase circuit for autonomy requires GIV’s modules/motifs that evolved only in the higher eukaryotes ( 24 ), and GIV is overexpressed in most cancers ( 28 ), we hypothesized that tumor cells may frequently assemble and utilize such an evolutionary advantage to achieve growth signaling autonomy at some stage during cancer progression. Using an integrated computational and experimental approach, we systematically analyzed these pair of cell lines for key hallmarks of cancer cells.…”

“…In fact, serum-free cell culture studies squarely implicate autocrine secretion of growth factors as key support for intracellular mechanisms that impart autonomy (reviewed in ( 23 )). Recently, using an integrated systems and experimental approach, a molecular machinery has been described which is critical for multiscale feedback control to achieve secretion-coupled autonomy in eukaryotic cells ( 24 ). The machinery is comprised of two species of GTPases, monomeric Arf1 and the heterotrimeric Gi, coupled by the multi-modular scaffold GIV, (i.e., G α- i nteracting v esicle associated protein; aka Girdin; gene CCDC88A ) within a closed-loop circuit that is localized at the Golgi ( 25 ).…”

Design principles of dose-response alignment in coupled GTPase switches

“…Subsequently, GIV increases the level of the GAP for mGTPase by molecular scaffolding action, and the activated tGT-Pase acts as a co-factor to maximally activate the GAP. This circuit was subsequently modeled for cell secretion (44) and for stability analysis (43).…”