Deciphering the role of protein kinase CK2 in the maturation/stability of F508del-CFTR

Targeting ubiquitination machinery in cystic fibrosis: Where do we stand?

Cystic Fibrosis (CF) is a genetic disease caused by mutations in CFTR gene expressing the anion selective channel CFTR located at the plasma membrane of different epithelial cells. The most commonly investigated variant causing CF is F508del. This mutation leads to structural defects in the CFTR protein, which are recognized by the endoplasmic reticulum (ER) quality control system. As a result, the protein is retained in the ER and degraded via the ubiquitin-proteasome pathway. Although blocking ubiquitination to stabilize the CFTR protein has long been considered a potential pharmacological approach in CF, progress in this area has been relatively slow. Currently, no compounds targeting this pathway have entered clinical trials for CF. On the other hand, the emergence of Orkambi initially, and notably the subsequent introduction of Trikafta/Kaftrio, have demonstrated the effectiveness of molecular chaperone-based therapies for patients carrying the F508del variant and even showed efficacy against other variants. These treatments directly target the CFTR variant protein without interfering with cell signaling pathways. This review discusses the limits and potential future of targeting protein ubiquitination in CF.

Emerging Therapies for Glioblastoma

Glioblastoma is most commonly a primary brain tumor and the utmost malignant one, with a survival rate of approximately 12-18 months. Glioblastoma is highly heterogeneous, demonstrating that different types of cells from the same tumor can manifest distinct gene expression patterns and biological behaviors. Conventional therapies such as temozolomide, radiation, and surgery have limitations. As of now, there is no cure for glioblastoma. Alternative treatment methods to eradicate glioblastoma are discussed in this review, including targeted therapies to PI3K, NFKβ, JAK-STAT, CK2, WNT, NOTCH, Hedgehog, and TGFβ pathways. The highly novel application of oncolytic viruses and nanomaterials in combating glioblastoma are also discussed. Despite scores of clinical trials for glioblastoma, the prognosis remains poor. Progress in breaching the blood-brain barrier with nanomaterials and novel avenues for targeted and combination treatments hold promise for the future development of efficacious glioblastoma therapies.

SUMOylation Inhibition Enhances Protein Transcription under CMV Promoter: A Lesson from a Study with the F508del-CFTR Mutant

Cystic fibrosis (CF) is a genetic disorder caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), a selective anion channel expressed in the epithelium of various organs. The most frequent mutation is F508del. This mutation leads to a misfolded CFTR protein quickly degraded via ubiquitination in the endoplasmic reticulum. Although preventing ubiquitination stabilizes the protein, functionality is not restored due to impaired plasma membrane transport. However, inhibiting the ubiquitination process can improve the effectiveness of correctors which act as chemical chaperones, facilitating F508del CFTR trafficking to the plasma membrane. Previous studies indicate a crosstalk between SUMOylation and ubiquitination in the regulation of CFTR. In this study, we investigated the potential of inhibiting SUMOylation to increase the effects of correctors and enhance the rescue of the F508del mutant across various cell models. In the widely used CFBE41o-cell line expressing F508del-CFTR, inhibiting SUMOylation substantially boosted F508del expression, thereby increasing the efficacy of correctors. Interestingly, this outcome did not result from enhanced stability of the mutant channel, but rather from augmented cytomegalovirus (CMV) promoter-mediated gene expression of F508del-CFTR. Notably, CFTR regulated by endogenous promoters in multiple cell lines or patient cells was not influenced by SUMOylation inhibitors.

KDM2A and KDM3B as Potential Targets for the Rescue of F508del-CFTR

Cystic fibrosis (CF) is caused by mutations in the gene encoding of the cystic fibrosis transmembrane conductance regulator (CFTR), an anion-selective plasma membrane channel that mainly regulates chloride transport in a variety of epithelia. More than 2000 mutations, most of which presumed to be disease-relevant, have been identified in the CFTR gene. The single CFTR mutation F508del (deletion of phenylalanine in position 508) is present in about 90% of global CF patients in at least one allele. F508del is responsible for the defective folding and processing of CFTR, failing to traffic to the plasma membrane and undergoing premature degradation via the ubiquitin–proteasome system. CFTR is subjected to different post-translational modifications (PTMs), and the possibility to modulate these PTMs has been suggested as a potential therapeutic strategy for the functional recovery of the disease-associated mutants. Recently, the PTM mapping of CFTR has identified some lysine residues that may undergo methylation or ubiquitination, suggesting a competition between these two PTMs. Our work hypothesis moves from the idea that favors methylation over ubiquitination, e.g., inhibiting demethylation could be a successful strategy for preventing the premature degradation of unstable CFTR mutants. Here, by using a siRNA library against all the human demethylases, we identified the enzymes whose downregulation increases F508del-CFTR stability and channel function. Our results show that KDM2A and KDM3B downregulation increases the stability of F508del-CFTR and boosts the functional rescue of the channel induced by CFTR correctors.

Protein kinase CK2: a potential therapeutic target for diverse human diseases

CK2 is a constitutively active Ser/Thr protein kinase, which phosphorylates hundreds of substrates, controls several signaling pathways, and is implicated in a plethora of human diseases. Its best documented role is in cancer, where it regulates practically all malignant hallmarks. Other well-known functions of CK2 are in human infections; in particular, several viruses exploit host cell CK2 for their life cycle. Very recently, also SARS-CoV-2, the virus responsible for the COVID-19 pandemic, has been found to enhance CK2 activity and to induce the phosphorylation of several CK2 substrates (either viral and host proteins). CK2 is also considered an emerging target for neurological diseases, inflammation and autoimmune disorders, diverse ophthalmic pathologies, diabetes, and obesity. In addition, CK2 activity has been associated with cardiovascular diseases, as cardiac ischemia-reperfusion injury, atherosclerosis, and cardiac hypertrophy. The hypothesis of considering CK2 inhibition for cystic fibrosis therapies has been also entertained for many years. Moreover, psychiatric disorders and syndromes due to CK2 mutations have been recently identified. On these bases, CK2 is emerging as an increasingly attractive target in various fields of human medicine, with the advantage that several very specific and effective inhibitors are already available. Here, we review the literature on CK2 implication in different human pathologies and evaluate its potential as a pharmacological target in the light of the most recent findings.

How can a traffic light properly work if it is always green? The paradox of CK2 signaling

CK2 is a constitutively active protein kinase that assuring a constant level of phosphorylation to its numerous substrates supports many of the most important biological functions. Nevertheless, its activity has to be controlled and adjusted in order to cope with the varying needs of a cell, and several examples of a fine-tune regulation of its activity have been described. More importantly, aberrant regulation of this enzyme may have pathological consequences, e.g. in cancer, chronic inflammation, neurodegeneration, and viral infection. Our review aims at summarizing our current knowledge about CK2 regulation. In the first part, we have considered the most important stimuli shown to affect protein kinase CK2 activity/expression. In the second part, we focus on the molecular mechanisms by which CK2 can be regulated, discussing controversial aspects and future perspectives.

Protein kinase CK2 inhibition as a pharmacological strategy

CK2 is a constitutively active Ser/Thr protein kinase which phosphorylates hundreds of substrates. Since they are primarily related to survival and proliferation pathways, the best-known pathological roles of CK2 are in cancer, where its targeting is currently being considered as a possible therapy. However, CK2 activity has been found instrumental in many other human pathologies, and its inhibition will expectably be extended to different purposes in the near future. Here, after a description of CK2 features and implications in diseases, we analyze the different inhibitors and strategies available to target CK2, and update the results so far obtained by their in vivo application.

Role of CK2 inhibitor CX-4945 in anti-cancer combination therapy - potential clinical relevance

BACKGROUND

Protein kinase CK2 inhibition has long been considered as an attractive anti-cancer strategy based on the following considerations: CK2 is a pro-survival kinase, it is frequently over-expressed in human tumours and its over-expression correlates with a worse prognosis. Preclinical evidence strongly supports the feasibility of this target and, although dozens of CK2 inhibitors have been described in the literature so far, CX-4945 (silmitasertib) was the first that entered into clinical trials for the treatment of both human haematological and solid tumours. However, kinase inhibitor monotherapies turned out to be effective only in a limited number of malignancies, probably due to the multifaceted causes that underlie them, supporting the emerging view that multi-targeted approaches to treat human tumours could be more effective.

CONCLUSIONS

In this review, we will address combined anti-cancer therapeutic strategies described so far which involve the use of CX-4945. Data from preclinical studies clearly show the ability of CX-4945 to synergistically cooperate with different classes of anti-neoplastic agents, thereby contributing to an orchestrated anti-tumour action against multiple targets. Overall, these promising outcomes support the translation of CX-4945 combined therapies into clinical anti-cancer applications.