The GNAQ T96S Mutation Affects Cell Signaling and Enhances the Oncogenic Properties of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC), the most common malignant tumor in the liver, grows and metastasizes rapidly. Despite advances in treatment modalities, the five-year survival rate of HCC remains less than 30%. We sought genetic mutations that may affect the oncogenic properties of HCC, using The Cancer Genome Atlas (TCGA) data analysis. We found that the GNAQ T96S mutation (threonine 96 to serine alteration of the Gαq protein) was present in 12 out of 373 HCC patients (3.2%). To examine the effect of the GNAQ T96S mutation on HCC, we transfected the SK-Hep-1 cell line with the wild-type or the mutant GNAQ T96S expression vector. Transfection with the wild-type GNAQ expression vector enhanced anchorage-independent growth, migration, and the MAPK pathways in the SK-Hep-1 cells compared to control vector transfection. Moreover, cell proliferation, anchorage-independent growth, migration, and the MAPK pathways were further enhanced in the SK-Hep-1 cells transfected with the GNAQ T96S expression vector compared to the wild-type GNAQ-transfected cells. In silico structural analysis shows that the substitution of the GNAQ amino acid threonine 96 with a serine may destabilize the interaction between the regulator of G protein signaling (RGS) protein and GNAQ. This may reduce the inhibitory effect of RGS on GNAQ signaling, enhancing the GNAQ signaling pathway. Single nucleotide polymorphism (SNP) genotyping analysis for Korean HCC patients shows that the GNAQ T96S mutation was found in only one of the 456 patients (0.22%). Our data suggest that the GNAQ T96S hotspot mutation may play an oncogenic role in HCC by potentiating the GNAQ signal transduction pathway.

PIK3CA gene mutations in the helical domain correlate with high tumor mutation burden and poor prognosis in metastatic breast carcinomas with late-line therapies

Nearly half of metastatic breast cancers (MBC) have genetic aberrations in the PI3K/AKT pathway. To investigate the distinct effect of these aberrations on MBC, 193 MBC patients who progressed after the early line (≤2) salvage treatment voluntarily received next generation sequencing (NGS) for a panel of 1,021 genes. 93 (48%) patients had genetic aberrations in the PI3K/AKT pathway. The number of patients with PIK3CA mutations in kinase domain (KD), helical domain (HD) and other domain (OD), were 36 (18.7%), 26 (13.5%), 10 (5.2%), respectively. 21 (10.9%) patients had mutations in PI3K/AKT pathway genes other than PIK3CA (P/A). Compared to PI3K/AKT-wild type (WT) patients, PIK3CA-HD patients had a significantly shorter progression-free survival (PFS) (Logrank p-value < 0.0001). PIK3CA-KD, PIK3CA-OD and other P/A mutations showed similar PFS to WT patients (Logrank p-value = 0.63). PIK3CA-HD patients had a distinct ctDNA mutation profile to patients with other PI3K/AKT mutations. PIK3CA-HD patients had a higher rate of FGFR and NF1 aberrations. In addition, more PIK3CA-HD carriers were TMB-high. Cox regression analyses suggested that PIK3CA-HD mutations, FGFR aberrations and high TMB were all significant risk factors for poor PFS. In conclusion, future research needs to focus more on the treatment strategies targeting PIK3CA-HD mutations.

A crystal structure of coil 1B of vimentin in the filamentous form provides a model of a high-order assembly of a vimentin filament

Vimentin is an intermediate filament (IF) protein that is expressed in leukocytes, fibroblasts and endothelial cells of blood vessels. Vimentin filaments contribute to structural stability of the cell membrane, organelle positioning and protein transport. Vimentin self-assembles into a dimer that subsequently forms high-order structures, including tetramers and octamers. The details of IF assembly at crystallographic resolutions are limited to the tetrameric form. We describe a crystal structure of a fragment of a vimentin rod domain (coil 1B) with a dimer of tetramers in the asymmetric unit. Coil 1B in the crystal is in an infinitely high-order filamentous assembly state, in which the tetramers are packed against each other laterally in an antiparallel fashion across the crystal lattice. In one of the directions of lateral packing, the tetramers pack against each other strictly head-to-tail, and in the orthogonal direction the tetramers pack in a staggered manner. This organization of the tetramers of coil 1B in the crystal lattice, together with previously reported biochemical and structural data, yield a model of high-order vimentin filament assembly.

DATABASE

Structural data are available in the PDB under the accession number 5WHF.

Role of the nucleotidyl cyclase helical domain in catalytically active dimer formation

Adenylyl and guanylyl cyclases are at the core of cellular signaling. Although the molecular mechanisms of the reactions catalyzed by these enzymes are well established, their structures and biophysical properties remain only partially characterized. Here, we report the structure of the cytosolic domain of a mycobacterial adenylyl cyclase Cya, an evolutionary ancestor of mammalian membrane adenylyl cyclases. The structure reveals the helical domain, a highly conserved structural element that links the catalytic and transmembrane portions of Cya. We show how helical domains bring together the catalytic domains to form functionally active dimers. Our data suggest that the disease-linked mutations in human nucleotidyl cyclases may disrupt the correct assembly of the helical domain, preventing the formation of an active dimeric enzyme.

Nucleotidyl cyclases, including membrane-integral and soluble adenylyl and guanylyl cyclases, are central components in a wide range of signaling pathways. These proteins are architecturally diverse, yet many of them share a conserved feature, a helical region that precedes the catalytic cyclase domain. The role of this region in cyclase dimerization has been a subject of debate. Although mutations within this region in various cyclases have been linked to genetic diseases, the molecular details of their effects on the enzymes remain unknown. Here, we report an X-ray structure of the cytosolic portion of the membrane-integral adenylyl cyclase Cya from Mycobacterium intracellulare in a nucleotide-bound state. The helical domains of each Cya monomer form a tight hairpin, bringing the two catalytic domains into an active dimerized state. Mutations in the helical domain of Cya mimic the disease-related mutations in human proteins, recapitulating the profiles of the corresponding mutated enzymes, adenylyl cyclase-5 and retinal guanylyl cyclase-1. Our experiments with full-length Cya and its cytosolic domain link the mutations to protein stability, and the ability to induce an active dimeric conformation of the catalytic domains. Sequence conservation indicates that this domain is an integral part of cyclase machinery across protein families and species. Our study provides evidence for a role of the helical domain in establishing a catalytically competent dimeric cyclase conformation. Our results also suggest that the disease-associated mutations in the corresponding regions of human nucleotidyl cyclases disrupt the normal helical domain structure.