Protein kinase CK2 phosphorylation of SAPS3 subunit increases PP6 phosphatase activity with Aurora A kinase

Identification of regulatory genes associated with POAG by integrating expression and sequencing data

BACKGROUND

Primary open-angle glaucoma (POAG) is a subtype of glaucoma that accounts for 60%~70% of all cases. Its pathogenic mechanism is intricate and its pathogenic process is concealed. Numerous significant biological processes associated with POAG continue to be elucidated.

METHODS

In this study, by exploring the expression data of POAG tissues and normal tissues, we mined the regulatory lncRNAs and mRNAs closely associated with the pathogenesis and progression of POAG by exploring a regulatory network of competing endogenous RNA (ceRNA), established by integrating gene expression data with the known lncRNA-miRNA and miRNA-mRNA-regulatory interactions. The key regulatory pathways and regulatory elements of POAG were identified by topological analysis. Simultaneously, the exome data of 28 cases with POAG and healthy controls were analyzed to identify high-frequency mutations and genes.

RESULTS

A total of 2712 differentially expressed genes were identified, including 1828 mRNAs and 884 lncRNAs. Network analysis suggested that lncRNAs such as HAGLR, HOTAIR and MIR29B2CHG, and mRNAs such as PPP6R3, BMPR2 and CFL2, may be involved in the onset and progression of POAG. In addition, 55 mutations with potential pathogenicity were identified.

CONCLUSION

These genes and mutations provide novel potential genetic heterogeneity and genetic susceptibility of POAG, as well as fresh suggestions for elucidating the molecular mechanism underlying the pathogenesis of POAG.

PPP6C negatively regulates oncogenic ERK signaling through dephosphorylation of MEK

Flux through the RAF-MEK-ERK protein kinase cascade is shaped by phosphatases acting on the core components of the pathway. Despite being an established drug target and a hub for crosstalk regulation, little is known about dephosphorylation of MEK, the central kinase within the cascade. Here, we identify PPP6C, a phosphatase frequently mutated or downregulated in melanoma, as a major MEK phosphatase in cells exhibiting oncogenic ERK pathway activation. Recruitment of MEK to PPP6C occurs through an interaction with its associated regulatory subunits. Loss of PPP6C causes hyperphosphorylation of MEK at activating and crosstalk phosphorylation sites, promoting signaling through the ERK pathway and decreasing sensitivity to MEK inhibitors. Recurrent melanoma-associated PPP6C mutations cause MEK hyperphosphorylation, suggesting that they promote disease at least in part by activating the core oncogenic pathway driving melanoma. Collectively, our studies identify a key negative regulator of ERK signaling that may influence susceptibility to targeted cancer therapies.

Through an shRNA screen, Cho et al. identify PPP6C as a phosphatase that inactivates the kinase MEK, sensitizing tumor cells to clinical MEK inhibitors. This study suggests that cancer-associated loss-of-function PPP6C mutations prevalent in melanoma serve to activate the core oncogenic RAF-MEK-ERK pathway that drives the disease.

A conserved acetylation switch enables pharmacological control of tubby-like protein stability

Tubby-like proteins (TULPs) are characterized by a conserved C-terminal domain that binds phosphoinositides. Collectively, mammalian TULP1-4 proteins play essential roles in intracellular transport, cell differentiation, signaling, and motility. Yet, little is known about how the function of these proteins is regulated in cells. Here, we present the protein–protein interaction network of TULP3, a protein that is responsible for the trafficking of G-protein-coupled receptors to cilia and whose aberrant expression is associated with severe developmental disorders and polycystic kidney disease. We identify several protein interaction nodes linked to TULP3 that include enzymes involved in acetylation and ubiquitination. We show that acetylation of two key lysine residues on TULP3 by p300 increases TULP3 protein abundance and that deacetylation of these sites by HDAC1 decreases protein levels. Furthermore, we show that one of these sites is ubiquitinated in the absence of acetylation and that acetylation inversely correlates with ubiquitination of TULP3. This mechanism is evidently conserved across species and is active in zebrafish during development. Finally, we identify this same regulatory module in TULP1, TULP2, and TULP4 and demonstrate that the stability of these proteins is similarly modulated by an acetylation switch. This study unveils a signaling pathway that links nuclear enzymes to ciliary membrane receptors via TULP3, describes a dynamic mechanism for the regulation of all tubby-like proteins, and explores how to exploit it pharmacologically using drugs.