Ribosomal protein S6 kinase beta-1 gene variants cause hypertrophic cardiomyopathy

BackgroundHypertrophic cardiomyopathy (HCM) is a genetic heart muscle disease with preserved or increased ejection fraction in the absence of secondary causes. Mutations in the sarcomeric protein-encoding genes predominantly cause HCM. However, relatively little is known about the genetic impact of signalling proteins on HCM.Methods and resultsHere, using exome and targeted sequencing methods, we analysed two independent cohorts comprising 401 Indian patients with HCM and 3521 Indian controls. We identified novel variants in ribosomal protein S6 kinase beta-1 (RPS6KB1 or S6K1) gene in two unrelated Indian families as a potential candidate gene for HCM. The two unrelated HCM families had the same heterozygous missense S6K1 variant (p.G47W). In a replication association study, we identified two S6K1 heterozygotes variants (p.Q49K and p.Y62H) in the UK Biobank cardiomyopathy cohort (n=190) compared with matched controls (n=16 479). These variants are neither detected in region-specific controls nor in the human population genome data. Additionally, we observed an S6K1 variant (p.P445S) in an Arab patient with HCM. Functional consequences were evaluated using representative S6K1 mutated proteins compared with wild type in cellular models. The mutated proteins activated the S6K1 and hyperphosphorylated the rpS6 and ERK1/2 signalling cascades, suggesting a gain-of-function effect.ConclusionsOur study demonstrates for the first time that the variants in the S6K1 gene are associated with HCM, and early detection of the S6K1 variant carriers can help to identify family members at risk and subsequent preventive measures. Further screening in patients with HCM with different ethnic populations will establish the specificity and frequency of S6K1 gene variants.

Discovery of a Potent and Highly Isoform-Selective Inhibitor of the Neglected Ribosomal Protein S6 Kinase Beta 2 (S6K2)

The ribosomal protein S6 kinase beta 2 (S6K2) is thought to play an important role in malignant cell proliferation, but is understudied compared to its closely related homolog S6 kinase beta 1 (S6K1). To better understand the biological function of S6K2, chemical probes are needed, but the high similarity between S6K2 and S6K1 makes it challenging to selectively address S6K2 with small molecules. We were able to design the first potent and highly isoform-specific S6K2 inhibitor from a known S6K1-selective inhibitor, which was merged with a covalent inhibitor engaging a cysteine located in the hinge region in the fibroblast growth factor receptor kinase (FGFR) 4 via a nucleophilic aromatic substitution (SNAr) reaction. The title compound shows a high selectivity over kinases with an equivalently positioned cysteine, as well as in a larger kinase panel. A good stability towards glutathione and Nα-acetyl lysine indicates a non-promiscuous reactivity pattern. Thus, the title compound represents an important step towards a high-quality chemical probe to study S6K2-specific signaling.

Over-expression of ribosomal protein S6 kinase A1 in human endometrial cancer.

Gynecologic cancers including cancers of the endometrium are a clinical problem (1-4). We mined published microarray data (5, 6) to discover genes associated with endometrial cancers by comparing transcriptomes of the normal endometrium and endometrial tumors from humans. We identified ribosomal protein S6 kinase A1, encoded by RPS6KA1, as among the most differentially expressed genes, transcriptome-wide, in cancers of the endometrium. RPS6KA1 was expressed at significantly higher levels in endometrial tumor tissues as compared to the endometrium. Importantly, in human endometrial cancer, primary tumor expression of RPS6KA1 was correlated with recurrence-free survival in white patients with low mutational burden. RPS6KA1 may be a molecule of interest in understanding the etiology or progression of human endometrial cancer.

Research Progress of 70 kDa Ribosomal Protein S6 Kinase (P70S6K) Inhibitors as Effective Therapeutic Tools for Obesity, Type II Diabetes and Cancer

At present, diseases such as obesity, type Ⅱ diabetes and cancer have brought serious health problems, which are closely related to mTOR pathway. 70 kDa ribosomal protein S6 kinase (p70S6K), as a significant downstream effector of mTOR, mediates protein synthesis, RNA processing, glucose homeostasis, cell growth and apoptosis. Inhibiting the function of p70S6K can reduce the risk of obesity which helps to treat dyslipidemia, enhance insulin sensitivity, and extend the life span of mammals. Therefore, p70S6K has become a potential target for the treatment of these diseases. So far, except for the first p70S6K specific inhibitor PF-4708671 developed by Pfizer and LY2584702 developed by Lilai, all of them are in preclinical research. This paper briefly introduces the general situation of p70S6K and reviews their inhibitors in recent years, which are mainly classified into two categories: natural compounds and synthetic compounds. In particular, their inhibitory activities, structure-activity relationships (SARs) and mechanisms are highlighted.

Phosphoproteomic Analysis of Neonatal Regenerative Myocardium Revealed Important Roles of Checkpoint Kinase 1 via Activating Mammalian Target of Rapamycin C1/Ribosomal Protein S6 Kinase b-1 Pathway

Background: In mammals, regenerative therapy after myocardial infarction is hampered by the limited regenerative capacity of adult heart, whereas a transient regenerative capacity is maintained in the neonatal heart. Systemic phosphorylation signaling analysis on ischemic neonatal myocardium might be helpful to identify key pathways involved in heart regeneration. Our aim was to define the kinase-substrate network in ischemic neonatal myocardium and to identify key pathways involved in heart regeneration after ischemic insult. Methods: Quantitative phosphoproteomics profiling was performed on infarct border zone of neonatal myocardium, and kinase-substrate network analysis revealed 11 kinases with enriched substrates and upregulated phosphorylation levels, including checkpoint kinase 1 (CHK1) kinase. The effect of CHK1 on cardiac regeneration was tested on Institute of Cancer Research CD1 neonatal and adult mice that underwent apical resection or myocardial infarction. Results: In vitro, CHK1 overexpression promoted whereas CHK1 knockdown blunted cardiomyocyte proliferation. In vivo, inhibition of CHK1 hindered myocardial regeneration on resection border zone in neonatal mice. In adult myocardial infarction mice, CHK1 overexpression on infarct border zone upregulated mammalian target of rapamycin C1/ribosomal protein S6 kinase b-1 pathway, promoted cardiomyocyte proliferation, and improved cardiac function. Inhibiting mammalian target of rapamycin activity by rapamycin blunted the neonatal cardiomyocyte proliferation induced by CHK1 overexpression in vitro. Conclusions: Our study indicates that phosphoproteome of neonatal regenerative myocardium could help identify important signaling pathways involved in myocardial regeneration. CHK1 is found to be a key signaling responsible for neonatal regeneration. Myocardial overexpression of CHK1 could improve cardiac regeneration in adult hearts by activating the mammalian target of rapamycin C1/ribosomal protein S6 kinase b-1 pathway. Thus, CHK1 might serve as a potential novel target in myocardial repair after myocardial infarction.