Prognostic Impact of Modulators of G proteins in Circulating Tumor Cells from Patients with Metastatic Colorectal Cancer.

Jorge Barbazan,Hongying Li,Pradipta Ghosh,Ying Dunkel,Ulrich Nitsche,Klaus-Peter Janssen,Karen Messer

doi:10.1038/srep22112

Abstract

The consequence of a loss of balance between G-protein activation and deactivation in cancers has been interrogated by studying infrequently occurring mutants of trimeric G-protein α-subunits and GPCRs. Prior studies on members of a newly identified family of non-receptor guanine nucleotide exchange factors (GEFs), GIV/Girdin, Daple, NUCB1 and NUCB2 have revealed that GPCR-independent hyperactivation of trimeric G proteins can fuel metastatic progression in a variety of cancers. Here we report that elevated expression of each GEF in circulating tumor cells (CTCs) isolated from the peripheral circulation of patients with metastatic colorectal cancer is associated with a shorter progression-free survival (PFS). The GEFs were stronger prognostic markers than two other markers of cancer progression, S100A4 and MACC1, and clustering of all GEFs together improved the prognostic accuracy of the individual family members; PFS was significantly lower in the high-GEFs versus the low-GEFs groups [H.R = 5, 20 (95% CI; 2,15–12,57)]. Because nucleotide exchange is the rate-limiting step in cyclical activation of G-proteins, the poor prognosis conferred by these GEFs in CTCs implies that hyperactivation of G-protein signaling by these GEFs is an important event during metastatic progression, and may be more frequently encountered than mutations in G-proteins and/or GPCRs.

Highlights

Heterotrimeric G proteins and G-protein-coupled receptors (GPCRs), which comprise the largest family of signaling hubs in eukaryotes, have long been recognized as crucial players in tumor growth and metastasis
We used two different probes for Daple: one that amplifies a region within the C-terminus which contains the guanine nucleotide exchange factors (GEFs) motif (CCDC88C) and one that amplifies a region within the N-terminus (CCDC88Cfl; can only recognize the full length form)
In the absence of bona-fide circulating tumor cells (CTCs) biomarkers in colorectal cancer (CRC), as positive controls we analyzed two established markers of aggressiveness and metastatic potential, S100A4 [S100 Calcium Binding Protein A410–15;] and MACC1 [metastasis associated in colon cancer 116,17;]

Summary

Introduction

Heterotrimeric G proteins and G-protein-coupled receptors (GPCRs), which comprise the largest family of signaling hubs in eukaryotes, have long been recognized as crucial players in tumor growth and metastasis (reviewed in[1,2]). A growing body of work by us and others[3,4,5,6] has defined a more frequent alternative mechanism by which cancer cells may hijack G protein signaling pathways and in this way fine tune to their advantage signaling networks that are triggered by growth factors, extracellular matrix, and other ligands. This alternative mechanism is a non-canonical mode of activation of G proteins that is not initiated by GPCRs, but instead by a recently identified family of non-receptor GEFs, called rheostats[7]. We evaluated the prognostic significance of individual members of this new family of modulators of G protein, and analyzed the combined predictive power of all members of this family

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Conclusion