The adaptors Grb10 and Grb14 are calmodulin-binding proteins

GRB10 rs1800504 Polymorphism Is Associated With the Risk of Coronary Heart Disease in Patients With Type 2 Diabetes Mellitus

Diabetic vascular complications are one of the main causes of death and disability. Previous studies have reported that genetic variation is associated with diabetic vascular complications. In this study, we aimed to investigate the association between GRB10 polymorphisms and susceptibility to type 2 diabetes mellitus (T2DM) vascular complications. Eight single nucleotide polymorphisms (SNPs) in the GRB10 gene were genotyped by MassARRAY system and 934 patients with type 2 diabetes mellitus (T2DM) were included for investigation. We found that GRB10 rs1800504 CC+CT genotypes were significantly associated with increased risk of coronary heart disease (CHD) compared with TT genotype (OR = 2.24; 95%CI: 1.36-3.70, p = 0.002). Consistently, levels of cholesterol (CHOL) (CC+CT vs. TT, 4.44 ± 1.25 vs. 4.10 ± 1.00 mmol/L; p = 0.009) and low density lipoprotein cholesterin (LDL-CH) (CC+CT vs. TT, 2.81 ± 1.07 vs. 2.53 ± 0.82 mmol/L; p = 0.01) in T2DM patients with TT genotype were significant lower than those of CC+CT genotypes. We further validated in MIHA cell that the total cholesterol (TC) level in GRB10-Mut was significantly reduced compared with GRB10-WT; p = 0.0005. Likewise, the reversed palmitic acid (PA) induced lipid droplet formation in GRB10-Mut was more effective than in GRB10-WT. These results suggest that rs1800504 of GRB10 variant may be associated with the blood lipids and then may also related to the risk of CHD in patients with T2DM.

Partners of wild type Grb7 and a mutant lacking its calmodulin-binding domain

Growth factor receptor bound protein 7 (Grb7) is a mammalian adaptor protein participating in signaling pathways implicated in cell migration, metastatic invasion, cell proliferation and tumor-associated angiogenesis. We expressed tagged versions of wild type Grb7 and the mutant Grb7Δ, lacking its calmodulin-binding domain (CaM-BD), in human embryonic kidney (HEK) 293 cells and rat glioma C6 cells to identify novel binding partners using shot-gun proteomics. Among the new identified proteins, we validated the ubiquitin-ligase Nedd4 (neural precursor cell expressed developmentally down-regulated protein 4), the heat-shock protein Hsc70/HSPA8 (heat shock cognate protein 70) and the cell cycle regulatory protein caprin-1 (cytoplasmic activation/proliferation-associated protein 1) in rat glioma C6 cells. Our results suggest a role of Grb7 in pathways where these proteins are implicated. These include protein trafficking and degradation, stress-response, chaperone-mediated autophagy, apoptosis and cell proliferation.

Grb7-derived calmodulin-binding peptides inhibit proliferation, migration and invasiveness of tumor cells while they enhance attachment to the substrate

The growth factor receptor bound protein 7 (Grb7) is a Ca²⁺-dependent calmodulin (CaM)-binding adaptor protein implicated, among other functions, in cell proliferation, migration and tumor-associated angiogenesis. The goal of this study was to determine whether a peptide based on the CaM binding site of Grb7 disrupts cellular processes, relevant for the malignancy of tumor cells, in which this adaptor protein is implicated. We designed synthetic myristoylated and non-myristoylated peptides corresponding to the CaM-binding domain of human Grb7 with the sequence ²⁴³RKLWKRFFCFLRRS²⁵⁶ and a variant peptide with the mutated sequence RKLERFFCFLRRE (W246E-ΔK247-S256E). The two non-myristoylated peptides bind dansyl-CaM with higher efficiency in the presence than in the absence of Ca²⁺ and they enter into the cell, as tested with 5(6)-carboxytetramethylrhodamine (TAMRA)-labeled peptides. The myristoylated and non-myristoylated peptides inhibit the proliferation, migration and invasiveness of A431 tumor cells while they enhance their adhesion to the substrate. The myristoylated peptides have stronger inhibitory effect than the non-myristoylated counterparts, in agreement with their expected higher cell-permeant capacity. The myristoylated and non-myristoylated W246E-ΔK247-S256E mutant peptide has a lesser inhibitory effect on cell proliferation as compared to the wild-type peptide. We also demonstrated that the myristoylated peptides were more efficient than the CaM antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibiting cell migration and equally efficient inhibiting cell proliferation.

Direct Interaction between Calmodulin and the Grb7 RA-PH Domain

Grb7 is a signalling adapter protein that engages activated receptor tyrosine kinases at cellular membranes to effect downstream pathways of cell migration, proliferation and survival. Grb7’s cellular location was shown to be regulated by the small calcium binding protein calmodulin (CaM). While evidence for a Grb7/CaM interaction is compelling, a direct interaction between CaM and purified Grb7 has not been demonstrated and quantitated. In this study we sought to determine this, and prepared pure full-length Grb7, as well as its RA-PH and SH2 subdomains, and tested for CaM binding using surface plasmon resonance. We report a direct interaction between full-length Grb7 and CaM that occurs in a calcium dependent manner. While no binding was observed to the SH2 domain alone, we observed a high micromolar affinity interaction between the Grb7 RA-PH domain and CaM, suggesting that the Grb7/CaM interaction is mediated through this region of Grb7. Together, our data support the model of a CaM interaction with Grb7 via its RA-PH domain.

The Role of Calmodulin in Tumor Cell Migration, Invasiveness, and Metastasis

Calmodulin (CaM) is the principal Ca²⁺ sensor protein in all eukaryotic cells, that upon binding to target proteins transduces signals encoded by global or subcellular-specific changes of Ca²⁺ concentration within the cell. The Ca²⁺/CaM complex as well as Ca²⁺-free CaM modulate the activity of a vast number of enzymes, channels, signaling, adaptor and structural proteins, and hence the functionality of implicated signaling pathways, which control multiple cellular functions. A basic and important cellular function controlled by CaM in various ways is cell motility. Here we discuss the role of CaM-dependent systems involved in cell migration, tumor cell invasiveness, and metastasis development. Emphasis is given to phosphorylation/dephosphorylation events catalyzed by myosin light-chain kinase, CaM-dependent kinase-II, as well as other CaM-dependent kinases, and the CaM-dependent phosphatase calcineurin. In addition, the role of the CaM-regulated small GTPases Rac1 and Cdc42 (cell division cycle protein 42) as well as CaM-binding adaptor/scaffold proteins such as Grb7 (growth factor receptor bound protein 7), IQGAP (IQ motif containing GTPase activating protein) and AKAP12 (A kinase anchoring protein 12) will be reviewed. CaM-regulated mechanisms in cancer cells responsible for their greater migratory capacity compared to non-malignant cells, invasion of adjacent normal tissues and their systemic dissemination will be discussed, including closely linked processes such as the epithelial–mesenchymal transition and the activation of metalloproteases. This review covers as well the role of CaM in establishing metastatic foci in distant organs. Finally, the use of CaM antagonists and other blocking techniques to downregulate CaM-dependent systems aimed at preventing cancer cell invasiveness and metastasis development will be outlined.

A coding and non-coding transcriptomic perspective on the genomics of human metabolic disease

Genome-wide association studies (GWAS), relying on hundreds of thousands of individuals, have revealed >200 genomic loci linked to metabolic disease (MD). Loss of insulin sensitivity (IS) is a key component of MD and we hypothesized that discovery of a robust IS transcriptome would help reveal the underlying genomic structure of MD. Using 1,012 human skeletal muscle samples, detailed physiology and a tissue-optimized approach for the quantification of coding (>18,000) and non-coding (>15,000) RNA (ncRNA), we identified 332 fasting IS-related genes (CORE-IS). Over 200 had a proven role in the biochemistry of insulin and/or metabolism or were located at GWAS MD loci. Over 50% of the CORE-IS genes responded to clinical treatment; 16 quantitatively tracking changes in IS across four independent studies (P = 0.0000053: negatively: AGL, G0S2, KPNA2, PGM2, RND3 and TSPAN9 and positively: ALDH6A1, DHTKD1, ECHDC3, MCCC1, OARD1, PCYT2, PRRX1, SGCG, SLC43A1 and SMIM8). A network of ncRNA positively related to IS and interacted with RNA coding for viral response proteins (P < 1 × 10⁻⁴⁸), while reduced amino acid catabolic gene expression occurred without a change in expression of oxidative-phosphorylation genes. We illustrate that combining in-depth physiological phenotyping with robust RNA profiling methods, identifies molecular networks which are highly consistent with the genetics and biochemistry of human metabolic disease.

Calmodulin as a protein linker and a regulator of adaptor/scaffold proteins

Calmodulin (CaM) is a universal regulator for a huge number of proteins in all eukaryotic cells. Best known is its function as a calcium-dependent modulator of the activity of enzymes, such as protein kinases and phosphatases, as well as other signaling proteins including membrane receptors, channels and structural proteins. However, less well known is the fact that CaM can also function as a Ca²⁺-dependent adaptor protein, either by bridging between different domains of the same protein or by linking two identical or different target proteins together. These activities are possible due to the fact that CaM contains two independently-folded Ca²⁺ binding lobes that are able to interact differentially and to some degree separately with targets proteins. In addition, CaM can interact with and regulates several proteins that function exclusively as adaptors. This review provides an overview over our present knowledge concerning the structural and functional aspects of the role of CaM as an adaptor protein and as a regulator of known adaptor/scaffold proteins.