Scaffold association factor B (SAFB) is required for expression of prenyltransferases and RAS membrane association

Regulation of protein prenylation

Prenyltransferases (PTases) are known to play a role in embryonic development, normal tissue homeostasis and cancer by posttranslationally modifying proteins involved in these processes. They are being discussed as potential drug targets in an increasing number of diseases, ranging from Alzheimer's disease to malaria. Protein prenylation and the development of specific PTase inhibitors (PTIs) have been subject to intense research in recent decades. Recently, the FDA approved lonafarnib, a specific farnesyltransferase inhibitor that acts directly on protein prenylation; and bempedoic acid, an ATP citrate lyase inhibitor that might alter intracellular isoprenoid composition, the relative concentrations of which can exert a decisive influence on protein prenylation. Both drugs represent the first approved agent in their respective substance class. Furthermore, an overwhelming number of processes and proteins that regulate protein prenylation have been identified over the years, many of which have been proposed as molecular targets for pharmacotherapy in their own right. However, certain aspects of protein prenylation, such as the regulation of PTase gene expression or the modulation of PTase activity by phosphorylation, have attracted less attention, despite their reported influence on tumor cell proliferation. Here, we want to summarize the advances regarding our understanding of the regulation of protein prenylation and the potential implications for drug development. Additionally, we want to suggest new lines of investigation that encompass the search for regulatory elements for PTases, especially at the genetic and epigenetic levels.

Insight into the Structural Basis for Dual Nucleic Acid-Recognition by the Scaffold Attachment Factor B2 Protein

The family of scaffold attachment factor B (SAFB) proteins comprises three members and was first identified as binders of the nuclear matrix/scaffold. Over the past two decades, SAFBs were shown to act in DNA repair, mRNA/(l)ncRNA processing and as part of protein complexes with chromatin-modifying enzymes. SAFB proteins are approximately 100 kDa-sized dual nucleic acid-binding proteins with dedicated domains in an otherwise largely unstructured context, but whether and how they discriminate DNA and RNA binding has remained enigmatic. We here provide the SAFB2 DNA- and RNA-binding SAP and RRM domains in their functional boundaries and use solution NMR spectroscopy to ascribe DNA- and RNA-binding functions. We give insight into their target nucleic acid preferences and map the interfaces with respective nucleic acids on sparse data-derived SAP and RRM domain structures. Further, we provide evidence that the SAP domain exhibits intra-domain dynamics and a potential tendency to dimerize, which may expand its specifically targeted DNA sequence range. Our data provide a first molecular basis of and a starting point towards deciphering DNA- and RNA-binding functions of SAFB2 on the molecular level and serve a basis for understanding its localization to specific regions of chromatin and its involvement in the processing of specific RNA species.

Drug targeting opportunities en route to Ras nanoclusters

Disruption of the native membrane organization of Ras by the farnesyltransferase inhibitor tipifarnib in the late 1990s constituted the first indirect approach to drug target Ras. Since then, our understanding of how dynamically Ras shuttles between subcellular locations has changed significantly. Ras proteins have to arrive at the plasma membrane for efficient MAPK-signal propagation. On the plasma membrane Ras proteins are organized into isoform specific proteo-lipid assemblies called nanocluster. Recent evidence suggests that Ras nanocluster have a specific lipid composition, which supports the recruitment of effectors such as Raf. Conversely, effectors possess lipid-recognition motifs, which appear to serve as co-incidence detectors for the lipid domain of a given Ras isoform. Evidence suggests that dimeric Raf proteins then co-assemble dimeric Ras in an immobile complex, thus forming the minimal unit of an active nanocluster. Here we review established and novel trafficking chaperones and trafficking factors of Ras, along with the set of lipid and protein modulators of Ras nanoclustering. We highlight drug targeting approaches and opportunities against these determinants of functional Ras membrane organization. Finally, we reflect on implications for Ras signaling in polarized cells, such as epithelia, which are a common origin of tumorigenesis.

Kirsten rat sarcoma inhibitors in clinical development against nonsmall cell lung cancer

PURPOSE OF REVIEW

The unique structure made Kirsten rat sarcoma (KRAS) 'undruggable' for quite an extended period. The functional mechanism of this small protein is well illustrated. However, there is no precision medicine for nonsmall cell lung cancer (NSCLC) patients burden with KRAS mutation. The attempts made by scientists to make challenge history against KRAS mutation and their druggable targets are worth elucidating.

RECENT FINDINGS

The appearance of orphan drug AMG510 in the market specifically targeting KRASG12C is a tremendous breakthrough. Several KRAS inhibitors are under development now. More studies focus on combo treatment of KRAS inhibition and immune checkpoint inhibitors (ICIs). Recent preclinical and clinical investigations have been reported that NSCLC patients with KRAS mutation can benefit from ICIs.

SUMMARY

The current review elucidates the development of KRAS inhibitors from basic research to clinical precision medicines. We retrospectively analyze the development of KRAS mutation targeting drugs and discuss the investigations for future development of KRAS inhibitors.

Identification of the Real Hub Gene and Construction of a Novel Prognostic Signature for Pancreatic Adenocarcinoma Based on the Weighted Gene Co-expression Network Analysis and Least Absolute Shrinkage and Selection Operator Algorithms

Background: Pancreatic adenocarcinoma (PAAD) has a considerably bad prognosis, and its pathophysiologic mechanism remains unclear. Thus, we aimed to identify real hub genes to better explore the pathophysiology of PAAD and construct a prognostic panel to better predict the prognosis of PAAD using the weighted gene co-expression network analysis (WGCNA) and the least absolute shrinkage and selection operator (LASSO) algorithms. Methods: WGCNA identified the modules most closely related to the PAAD stage and grade based on the Gene Expression Omnibus. The module genes significantly associated with PAAD progression and prognosis were considered as the real hub genes. Eligible genes in the most significant module were selected for construction and validation of a multigene prognostic signature based on the LASSO-Cox regression analysis in The Cancer Genome Atlas and the International Cancer Genome Consortium databases, respectively. Results: The brown module identified by WGCNA was most closely associated with the clinical characteristics of PAAD. Scaffold attachment factor B (SAFB) was significantly associated with PAAD progression and prognosis, and was identified as the real hub gene of PAAD. Moreover, both transcriptional and translational levels of SAFB were significantly lower in PAAD tissues compared with normal pancreatic tissues. In addition, a novel multigene-independent prognostic signature consisting of SAFB, SP1, and SERTAD3 was identified and verified. The predictive accuracy of our signature was superior to that of previous studies, especially for predicting 3- and 5-year survival probabilities. Furthermore, a prognostic nomogram based on independent prognostic variables was developed and validated using calibration curves. The predictive ability of this nomogram was also superior to the well-established AJCC stage and histological grade. The potential mechanisms of different prognoses between the high- and low-risk subgroups were also investigated using functional enrichment analysis, GSEA, ssGSEA, immune checkpoint analysis, and mutation profile analysis. Conclusion: SAFB was identified as the real hub gene of PAAD. A novel multigene-independent prognostic signature was successfully identified and validated to better predict PAAD prognosis. An accurate nomogram was also developed and verified to aid in the accurate treatment of tumors, as well as in early intervention.

Post-translational modification of RAS proteins

Mutations of RAS genes drive cancer more frequently than any other oncogene. RAS proteins integrate signals from a wide array of receptors and initiate downstream signaling through pathways that control cellular growth. RAS proteins are fundamentally binary molecular switches in which the off/on state is determined by the binding of GDP or GTP, respectively. As such, the intrinsic and regulated nucleotide-binding and hydrolytic properties of the RAS GTPase were historically believed to account for the entirety of the regulation of RAS signaling. However, it is increasingly clear that RAS proteins are also regulated by a vast array of post-translational modifications (PTMs). The current challenge is to understand what are the functional consequences of these modifications and which are physiologically relevant. Because PTMs are catalyzed by enzymes that may offer targets for drug discovery, the study of RAS PTMs has been a high priority for RAS biologists.

Ras isoform-specific expression, chromatin accessibility, and signaling

The anchorage of Ras isoforms in the membrane and their nanocluster formations have been studied extensively, including their detailed interactions, sizes, preferred membrane environments, chemistry, and geometry. However, the staggering challenge of their epigenetics and chromatin accessibility in distinct cell states and types, which we propose is a major factor determining their specific expression, still awaits unraveling. Ras isoforms are distinguished by their C-terminal hypervariable region (HVR) which acts in intracellular transport, regulation, and membrane anchorage. Here, we review some isoform-specific activities at the plasma membrane from a structural dynamic standpoint. Inspired by physics and chemistry, we recognize that understanding functional specificity requires insight into how biomolecules can organize themselves in different cellular environments. Within this framework, we suggest that isoform-specific expression may largely be controlled by the chromatin density and physical compaction, which allow (or curb) access to "chromatinized DNA." Genes are preferentially expressed in tissues: proteins expressed in pancreatic cells may not be equally expressed in lung cells. It is the rule-not an exception, and it can be at least partly understood in terms of chromatin organization and accessibility state. Genes are expressed when they can be sufficiently exposed to the transcription machinery, and they are less so when they are persistently buried in dense chromatin. Notably, chromatin accessibility can similarly determine expression of drug resistance genes.

A Novel TGF-β Risk Score Predicts the Clinical Outcomes and Tumour Microenvironment Phenotypes in Bladder Cancer

Background

The TGF-β pathway plays critical roles in numerous malignancies. Nevertheless, its potential role in prognosis prediction and regulating tumour microenvironment (TME) characteristics require further elucidation in bladder cancer (BLCA).

Methods

TGF-β-related genes were comprehensively summarized from several databases. The TCGA-BLCA cohort (training cohort) was downloaded from the Cancer Genome Atlas, and the independent validation cohorts were gathered from Xiangya Hospital (Xinagya cohort) and Gene Expression Omnibus. Initially, we identified differentially expressed TGF-β genes (DEGs) between cancer and normal tissues. Subsequently, univariate Cox analysis was applied to identify prognostic DEGs, which were further used to develop the TGF-β risk score by performing LASSO and multivariate Cox analyses. Then, we studied the role of the TGF-β risk score in predicting prognosis and the TME phenotypes. In addition, the role of the TGF-β risk score in guiding precision treatments for BLCA has also been assessed.

Results

We successfully constructed a TGF-β risk score with an independent prognostic prediction value. A high TGF-β risk score indicated an inflamed TME, which was supported by the positive relationships between the risk score, enrichment scores of anticancer immunity steps, and the infiltration levels of tumour-infiltrating immune cells. In addition, the risk score positively correlated with the expression of several immune checkpoints and the T cell inflamed score. Consistently, the risk score was positively related to the enrichment scores of most immunotherapy-positive pathways. In addition, the sensitivities of six common chemotherapeutic drugs were positively associated with the risk score. Furthermore, higher risk score indicated higher sensitivity to radiotherapy and EGFR-targeted therapy. On the contrary, patients with low-risk scores were more sensitive to targeted therapies, including the blockade of FGFR3 and WNT-β-catenin networks.

Conclusions

We first constructed and validated a TGF-β signature that could predict the prognosis and TME phenotypes for BLCA. More importantly, the TGF-β risk score could aid in individual precision treatment for BLCA.