Reciprocal Negative Regulation between the Guanine Nucleotide Exchange Factor C3G and  -Catenin

Abstract

The guanine nucleotide exchange factor C3G (RAPGEF1) regulates proliferation, migration, and differentiation of cells and is essential for mammalian embryonic development. The molecular effectors of C3G dependent functions are poorly understood. Here we report that C3G functions as a negative regulator of β-catenin, a major player in pathways known to be deregulated in human cancers. In mammalian cells, C3G is present in a complex with cellular β-catenin. The proline rich Crk binding region of C3G and residues 90-525 of β-catenin are sufficient for the interaction. Knockdown of cellular C3G stimulated, and its overexpression repressed, β-catenin/TCF transcription activity. C3G acts by destabilizing β-catenin protein and inhibiting its nuclear accumulation. Nuclear extracts of C3G overexpressing cells showed reduced binding to TCF consensus oligos. C3G exerts its effects independent of its function as an exchange factor. It also inhibits stability and activity of an N-terminal deletion construct of β-catenin that is not subject to GSK3β dependent phosphorylation, suggesting that C3G exerts its effect independent of GSK3β. β-catenin repression by C3G was not significantly altered in the presence of proteasome inhibitors, MG132 or lactacystin, suggesting that alternate mechanisms are engaged by C3G to cause β-catenin turnover. C3G expression represses β-catenin target gene expression, and stable clones of MCF-7 breast cancer cells expressing C3G showed reduced migration. Activation of cellular β-catenin or expression of constitutively active β-catenin resulted in reduced C3G expression, indicating that C3G gene expression is negatively regulated by β-catenin. Our results identify a novel property of C3G in functioning as a negative regulator of β-catenin signaling by promoting its degradation. In addition, we show that β-catenin inhibits C3G expression, forming a feedback loop. KeywordsC3G, β-catenin, guanine nucleotide exchange factor, signaling, GSK3βOriginal Article C3G interacts with and inhibits β-catenin function / Dayma et al.

Molecular etiology of an indolent lymphoproliferative disorder determined by whole-genome sequencing

“…This position is not found to be altered in ExAC, and the mutant allele is expressed in the tumor (Supplemental Table S1). One of the other genes having somatic mutations in this patient, but at a lower frequency in lymphoid samples in COSMIC, is RAPGEF1 , which, like APC , encodes a negative regulator of β-catenin ( Dayma et al 2012 ). The mutation in RAPGEF1 , Y572C, occurs at the same position as COSMIC mutation 1901064 (which is Y572H).…”

C3G (RapGEF1) localizes to the mother centriole and regulates centriole division and primary cilia dynamics

“…It is a 140 kDa protein with a catalytic domain at the C terminus and a central region containing multiple polyproline tracts called Crk binding region (CBR). It activates GTPases of Ras & Rho family and interacts with several proteins like Crk, SFKs, c-Abl, TCPTP & β-catenin (Dayma et al, 2012; Gotoh et al, 1995; Knudsen et al, 1994; Mitra et al, 2011; Mochizuki et al, 2000; Radha et al, 2007; Shivakrupa et al, 2003). It can participate in signaling as a GEF as well as an adaptor molecule.…”

“…Introduction of a hypomorphic allele prolongs survival but the embryos show defects in development of brain and other organ systems (Ohba et al, 2001; Voss et al, 2003). We have earlier shown that C3G interacts with, and regulates stability and activity of β-catenin (Dayma et al, 2012). In addition, C3G expression is regulated by β-catenin activity.…”

C3G dynamically associates with nuclear speckles and regulates mRNA splicing

“…C3G targets GTPases Rap1, Rap2, R-Ras, and TC10 ( Gotoh et al , 1995 ; Mochizuki et al , 2000 ) and interacts with signaling molecules like Hck, Src, Crk, c-Abl, TC-48, and β-catenin ( Knudsen et al , 1994 ; Tanaka et al , 1994 ; Shivakrupa et al , 2003 ; Radha et al , 2007 ; Mitra et al , 2011 ; Dayma et al , 2012 ). C3G suppresses β-catenin activity, a determinant of cell fate decisions ( Dayma et al , 2012 ). C3G levels increase and are required for differentiation of muscle and neuronal cells ( Radha et al , 2008 ; Sasi Kumar et al , 2015 ).…”