The fate of eukaryotic proteins, from their synthesis to destruction, is supervised by the ubiquitin–proteasome system (UPS). The UPS is the primary pathway responsible for selective proteolysis of intracellular proteins, which is guided by covalent attachment of ubiquitin to target proteins by E1 (activating), E2 (conjugating), and E3 (ligating) enzymes in a process known as ubiquitylation. The UPS can also regulate protein synthesis by influencing multiple steps of RNA (ribonucleic acid) metabolism. Here, recent publications concerning the interplay between the UPS and different types of RNA are reviewed. This interplay mainly involves specific RNA‐binding E3 ligases that link RNA‐dependent processes with protein ubiquitylation. The emerging understanding of their modes of RNA binding, their RNA targets, and their molecular and cellular functions are primarily focused on. It is discussed how the UPS adapted to interact with different types of RNA and how RNA molecules influence the ubiquitin signaling components.

Keratin 8/18, a simple epithelia specific keratin pair, is often aberrantly expressed in squamous cell carcinomas (SCC) where its expression is correlated with increased invasion and poor prognosis. Majority of Keratin 8 (K8) functions are governed by its phosphorylation at Serine (head-domain) and Serine (tail-domain) residues. Although, deregulation of K8 phosphorylation is associated with progression of different carcinomas, its role in skin-SCC and the underlying mechanism is obscure. In this direction, we performed tandem mass tag-based quantitative phosphoproteomics by expressing K8 wild type, phosphodead, and phosphomimetic mutants in K8-deficient A431 cells. Further analysis of our phosphoproteomics data showed a significant proportion of total phosphoproteome associated with migratory, proliferative, and invasive potential of these cells to be differentially phosphorylated. Differential phosphorylation of CDK1 , EIF4EBP1 , EIF4B , AKT1S1 , CTTN1 , and CAP1 in K8-S73A/D mutant and CTTN1 , BUB1B , and CARHSP1 in K8-S431A/D mutants as well as some anonymous phosphosites including MYC , ZYX , and PNN could be potential candidates associated with K8 phosphorylation mediated tumorigenicity. Biochemical validation followed by phenotypic analysis further confirmed our quantitative phosphoproteomics data. In conclusion, our study provides the first global picture of K8 site-specific phosphorylation function in neoplastic progression of A431 cells and suggests various potential starting points for further mechanistic studies.

Budding yeast Pichia pastoris has highly advanced secretory pathways resembling mammalian systems, an advantage that makes it a suitable model system to study vesicular trafficking. Golgins are large Golgi-resident proteins, primarily reported to play role in cargo vesicle capture, but details of such mechanisms are yet to be deciphered. Golgins that localize to the Golgi via their GRIP domain, a C-terminal Golgi anchoring domain, are known as GRIP domain Golgins. In this present study, we have identified and functionally characterized a homologue of one such GRIP domain Golgin protein, Imh1, from the budding yeast P. pastoris. We have demonstrated that the GRIP domain present at the C-terminal of P. pastoris Imh1 (PpImh1) functions as its Golgi-targeting sequence. Using a combination of yeast two-hybrid analysis, dynamic light scattering and electron microscopy, we have shown that PpImh1 can self-associate and form a homodimer. Analysis of purified recombinant PpImh1 by CD spectroscopy indicates the presence of an 85% α-helical structure, a characteristic of high-content α-helical coiled-coil sequences normally present in other Golgin family proteins. Two-hybrid analysis indicated self-interaction between C-terminal fragments, yet N-terminal fragments do not mediate any such form of self-interaction, suggesting that PpImh1 may form a parallel dimer. Electron microscopy data indicates that PpImh1 forms extended rod-like homo-dimeric molecules with splayed N-terminal end which can act as a tether for capturing vesicles. Our study provides the first evidence in support of the dimeric Y-shaped structure for any Golgin in the budding yeast.

Proteome Xchange Consortium via PRIDE database (dataset identifier PXD007206).