The Tumor-suppressive Small GTPase DiRas1 Binds the Noncanonical Guanine Nucleotide Exchange Factor SmgGDS and Antagonizes SmgGDS Interactions with Oncogenic Small GTPases

Abstract

The small GTPase DiRas1 has tumor-suppressive activities, unlike the oncogenic properties more common to small GTPases such as K-Ras and RhoA. Although DiRas1 has been found to be a tumor suppressor in gliomas and esophageal squamous cell carcinomas, the mechanisms by which it inhibits malignant phenotypes have not been fully determined. In this study, we demonstrate that DiRas1 binds to SmgGDS, a protein that promotes the activation of several oncogenic GTPases. In silico docking studies predict that DiRas1 binds to SmgGDS in a manner similar to other small GTPases. SmgGDS is a guanine nucleotide exchange factor for RhoA, but we report here that SmgGDS does not mediate GDP/ GTP exchange on DiRas1. Intriguingly, DiRas1 acts similarly to a dominant-negative small GTPase, binding to SmgGDS and inhibiting SmgGDS binding to other small GTPases, including K-Ras4B, RhoA, and Rap1A. DiRas1 is expressed in normal breast tissue, but its expression is decreased in most breast cancers, similar to its family member DiRas3 (ARHI). DiRas1 inhibits RhoA-and Smg-GDS-mediated NF-B transcriptional activity in HEK293T cells. We also report that DiRas1 suppresses basal NF-B activation in breast cancer and glioblastoma cell lines. Taken together, our data support a model in which DiRas1 expression inhibits malignant features of cancers in part by nonproductively binding to SmgGDS and inhibiting the binding of other small GTPases to SmgGDS.

RNAa and Vector-Mediated Overexpression of DIRAS1 Suppresses Tumor Growth and Migration in Renal Cell Carcinoma

“…DIRAS1 has been suggested as a tumor suppresser in several human cancers, including colorectal cancer, 9 esophageal squamous cell carcinoma, 5 and glioma 6 . The mechanism underlying these tumor-suppressive activities might contribute to its ability to bind to SmgGDS, a protein that induces the activation of several oncogenic GTPases 18 . The ERK1/2, p38 mitogen-activated protein kinase (MAPK), and nuclear factor κB (NF-κB) pathways can be inhibited by the restoration of DIRAS1 expression 5, 18.…”

“…The mechanism underlying these tumor-suppressive activities might contribute to its ability to bind to SmgGDS, a protein that induces the activation of several oncogenic GTPases 18 . The ERK1/2, p38 mitogen-activated protein kinase (MAPK), and nuclear factor κB (NF-κB) pathways can be inhibited by the restoration of DIRAS1 expression 5, 18. Studies have indicated that downregulation of DIRAS1 is attributed to DNA copy number loss, LOH, and hypermethylation 5, 9.…”

Generalized myoclonic epilepsy with photosensitivity in juvenile dogs caused by a defective DIRAS family GTPase 1

“…The biological function of DIRAS1 in mammals is poorly characterized. DIRAS1 has been suggested to function as a tumor suppressor in glioblastoma and other tumor cell lines through the inhibition of Ras-mediated transformation, altered NF-κB transcription activity, diminished ERK1/2 and MAPK signaling, and antagonization of pro-oncogenic small Ras GTPases (44). Studies in C. elegans have demonstrated that the DIRAS1 and exchange protein directly activated by cAMP (EPAC) orthologs colocalize at the presynaptic membranes and are needed for the maintenance of normal presynaptic acetylcholine release at neuromuscular junctions (17).…”

GEF mechanism revealed by the structure of SmgGDS-558 and farnesylated RhoA complex and its implication for a chaperone mechanism

“…SmgGDS also acts as a chaperone protein for small GTPases having a CaaX motif, in addition to a GEF for Rho family proteins (5)(6)(7)(8)(9)(10). SmgGDS interacts with various small GTPases possessing a Cterminal polybasic region (PBR) upstream of the CaaX motif in a hypervariable region (HVR) (5,6,(11)(12)(13). SmgGDS is overexpressed in nonsmall cell lung carcinoma (14,15), prostate cancer (16), breast cancer (15,17), and pancreatic cancer (15).…”