👤 Craig McFarlane

Golgi_traff is a Pfam clan containing two members, Dymeclin (DYM) and HID1 domain-containing protein (HID). Interrogation of over 900 eukaryotic genomes with sequence models showed that both are ancient eukaryotic genes, which have exhibited different paths of gene loss, including from major taxonomic groups. For example, the Metazoa have both genes, whereas the Viridiplantae and Dikarya have lost HID and DYM, respectively. A unique replication event occurred within the genus Schizosaccharomyces in that all sequenced species possess three HID-encoding paralogs, whereas its nearest fungal relatives and other eukaryotes are almost exclusively monogenic. A phylogenetic analysis of yeasts revealed that the Golgi-resident paralog Human ortholog 3 (SPAC17A5.16) is more similar to the HID of other yeasts than to its paralogs. Transmission electron microscopy revealed that the SPAC17A5.16 mutant lacks a stacked Golgi apparatus (GA) form, suggesting a role in maintaining GA structure. Altered proliferation of the SPAC17A5.16 mutant in response to GA disrupting chemical agents indicated a perturbation of GA-related functions. Structural models suggest SPAC17A5.16 has a long, disordered N-terminal region that may facilitate anchoring to GA membranes. A modification to Schizosaccharomyces HID nomenclature is proposed to reflect their evolutionary and functional characteristics. The potential of the Golgi_traff clan to serve as a model for the diversification of protein function according to the concepts of sub/neofunctionalization is discussed. Show less

To date a plethora of evidence has clearly demonstrated that continued high calorie intake leads to insulin resistance and type-2 diabetes with or without obesity. However, the necessary signals that initiate insulin resistance during high calorie intake remain largely unknown. Our results here show that in response to a regimen of high fat or high glucose diets, Mstn levels were induced in muscle and liver of mice. High glucose- or fat-mediated induction of Mstn was controlled at the level of transcription, as highly conserved carbohydrate response and sterol-responsive (E-box) elements were present in the Mstn promoter and were revealed to be critical for ChREBP (carbohydrate-responsive element-binding protein) or SREBP1c (sterol regulatory element-binding protein 1c) regulation of Mstn expression. Further molecular analysis suggested that the increased Mstn levels (due to high glucose or fatty acid loading) resulted in increased expression of Cblb in a Smad3-dependent manner. Casitas B-lineage lymphoma b (Cblb) is an ubiquitin E3 ligase that has been shown to specifically degrade insulin receptor substrate 1 (IRS1) protein. Consistent with this, our results revealed that elevated Mstn levels specifically up-regulated Cblb, resulting in enhanced ubiquitin proteasome-mediated degradation of IRS1. In addition, over expression or knock down of Cblb had a major impact on IRS1 and pAkt levels in the presence or absence of insulin. Collectively, these observations strongly suggest that increased glucose levels and high fat diet, both, result in increased circulatory Mstn levels. The increased Mstn in turn is a potent inducer of insulin resistance by degrading IRS1 protein via the E3 ligase, Cblb, in a Smad3-dependent manner. Show less

Ran is a small ras-related GTPase that controls the nucleocytoplasmic exchange of macromolecules across the nuclear envelope. It binds to chromatin early during nuclear formation and has important roles during the eukaryotic cell cycle, where it regulates mitotic spindle assembly, nuclear envelope formation and cell cycle checkpoint control. Like other GTPases, Ran relies on the cycling between GTP-bound and GDP-bound conformations to interact with effector proteins and regulate these processes. In nucleocytoplasmic transport, Ran shuttles across the nuclear envelope through nuclear pores. It is concentrated in the nucleus by an active import mechanism where it generates a high concentration of RanGTP by nucleotide exchange. It controls the assembly and disassembly of a range of complexes that are formed between Ran-binding proteins and cellular cargo to maintain rapid nuclear transport. Ran also has been identified as an essential protein in nuclear envelope formation in eukaryotes. This mechanism is dependent on importin-β, which regulates the assembly of further complexes important in this process, such as Nup107-Nup160. A strong body of evidence is emerging implicating Ran as a key protein in the metastatic progression of cancer. Ran is overexpressed in a range of tumors, such as breast and renal, and these perturbed levels are associated with local invasion, metastasis and reduced patient survival. Furthermore, tumors with oncogenic KRAS or PIK3CA mutations are addicted to Ran expression, which yields exciting future therapeutic opportunities. Show less