IGF-1R nuclear import and recruitment to chromatin involves both alpha and beta subunits

Mature type 1 insulin-like growth factor receptors (IGF-1Rs) are heterotetrameric structures comprising two extracellular α-subunits disulphide-bonded to two transmembrane β-subunits with tyrosine kinase activity. IGF-1R is a well-known cell surface mediator of malignant growth, with an incompletely understood role upon nuclear import as a transcriptional regulator. Previous characterisation of nuclear IGF-1R focused on IGF-1Rβ. Here, we aimed to clarify the source of nuclear IGF-1R and investigate whether α-subunits contribute to nuclear IGF-1R function. Using prostate cancer cell lines DU145 and 22Rv1 we detected nuclear α- and β-subunits, with increase in nuclear signal upon IGF-treatment and reduction in response to IGF-1R inhibitor BMS-754807. Following biotinylation of cell surface proteins, biotinylated α- and β-subunits were detected in nuclear extracts of both cell lines. Furthermore, α- and β-subunits reciprocally co-precipitated from nuclear extract. Finally, we detected recruitment of both subunits to regulatory regions of chromatin, including the promoter of the oncogene JUN, that we previously identified in ChIP-seq as sites of IGF-1Rβ enrichment. These data confirm the cell surface origin of nuclear IGF-1R, suggest the presence of nuclear αβ complexes and reveal that both IGF-1Rα- and β-subunits contribute to pro-tumorigenic functions of nuclear IGF-1R.

Detection of the germline specific NAC protein paralog enriched by intrinsically disordered regions in Drosophila melanogaster

Nascent polypeptide associated complex (NAC) consisting of α- and β-subunits is an essential conserved ubiquitously expressed ribosome-associated protein in eukaryotes. NAC is considered as a chaperone and co-translational regulator of nascent protein sorting providing homeostasis of cellular proteins. Here we discovered the germinal cell specific NAC (gNAC) homologue, which differs from the ubiquitously expressed NAC by the presence of expanded intrinsically disordered regions (IDRs) at the N- and C-ends of the α- and β-subunits, respectively. We propose these evolutionary acquisition of long IDRs drive gNAC to endow both the specific conformational plasticity for binding client proteins and novel functions regulated by post-transcriptional modifications (PTM). At the same time, we demonstrated that the well-known lethal effect of the loss of ubiquitous NAC-β is suppressed by ectopic expression of its germinal paralog indicating the absence of strict functional differences between the ubiquitous and germline NAC-β subunit paralogs for protein homeostasis.

Towards understanding non-equivalence of α and β subunits within human hemoglobin in conformational relaxation and molecular oxygen rebinding

Picosecond to millisecond laser time-resolved transient absorption spectroscopy was used to study molecular oxygen (O2) rebinding and conformational relaxation following O2 photodissociation in the α and β subunits within human...

The role of heterotrimeric G proteins in the control of the development of symbiosis of leguminous plants with nodule bacteria

In this work, we analyzed the localization and effect of suppression of gene expression of β-subunits of G-proteins on nodule formation. The possible interaction of α- and β-subunits with a set of signal regulators in vitro was revealed.

Acidified Pepsin Promotes Laryngeal Precancerosis by Upregulating H+/K+-ATPase and Activating Mitophagy in Laryngeal Epithelial Cells

Background: Although laryngopharyngeal reflux (LPR) has been implicated in various upper aerodigestive tract and laryngeal diseases, the underlying mechanisms remain elusive. In this study, we investigated the role of gastric acidified pepsin in laryngeal precancerosis. Methods: The in vitro and in vivo effects of acidified pepsin on H+/K+-ATPase expression and autophagy/mitophagy induction in mouse laryngeal epithelial cells were assessed by hematoxylin and eosin staining, immunohistochemistry, CCK-8 assay, flow cytometry, Western blotting, and quantitative real-time PCR. Additionally, the levels of pepsin and H+/K+-ATPase α and β subunits in 31 human laryngeal mucosal specimens were assessed by immunohistochemical staining. Results: Acidified pepsin (pH=3) enhanced the growth and survival of mouse laryngeal epithelial cells in vitro and promoted laryngeal mucosal thickening and laryngeal epithelial cell growth in vivo. Furthermore, acidified pepsin promoted autophagy/mitophagy induction, accompanied by a significant decrease in mitochondrial membrane potential (MMP). Inhibition of autophagy by chloroquine abolished the ability of acidified pepsin to promote mitophagy and cell growth in laryngeal epithelial cells. Additionally, chloroquine promoted cell apoptosis and further reduced MMP in laryngeal epithelial cells treated with acidified pepsin. The expression levels of pepsin and H+/K+-ATPase α and β subunits in 31 human laryngeal mucosa specimens were 51.6%, 48.4%, and 48.4%, respectively. Importantly, the pepsin level was correlated with the H+/K+-ATPase β subunit level. H+/K+-ATPase upregulation in laryngeal epithelial cells in response to acidified pepsin was essential for the mitophagy-promoting effect of acidified pepsin. H+/K+-ATPase knockout or inhibition further reduced MMP in the presence of acidified pepsin. Conclusions: Our findings suggest that in an acidic environment, pepsin promotes laryngeal epithelial cell growth and survival by upregulating H+/K+-ATPase and activating mitophagy, potentially leading to laryngeal precancerosis.

An evolutionarily distinct chaperone promotes 20S proteasome α-ring assembly in plants

ABSTRACTThe core protease (CP) subcomplex of the 26S proteasome houses the proteolytic active sites and assumes a barrel shape comprised of four co-axially stacked heptameric rings formed by structurally related α- and β-subunits. CP biogenesis typically begins with the assembly of the α-ring, which then provides a template for β-subunit integration. In eukaryotes, α-ring assembly is partially mediated by two hetero-dimeric chaperones, termed Pba1–Pba2 (Add66) and Pba3–Pba4 (also known as Irc25–Poc4) in yeast. Pba1–Pba2 initially promotes orderly recruitment of the α-subunits through interactions between their C-terminal HbYX or HbF motifs and pockets at the α5–α6 and α6–α7 interfaces. Here, we identified PBAC5 as a fifth α-ring assembly chaperone in Arabidopsis that directly binds the Pba1 homolog PBAC1 to form a trimeric PBAC5–PBAC1–PBAC2 complex. PBAC5 harbors a HbYX motif that docks with a pocket between the α4 and α5 subunits during α-ring construction. Arabidopsis lacking PBAC5, PBAC1 and/or PBAC2 are hypersensitive to proteotoxic, salt and osmotic stresses, and display proteasome assembly defects. Remarkably, whereas PBAC5 is evolutionarily conserved among plants, sequence relatives are also dispersed within other kingdoms, including a scattered array of fungal, metazoan and oomycete species.