The Effect of CDK6 Expression on DNA Methylation and DNMT3B Regulation

CDK6 Degradation Is Counteracted by p16INK4A and p18INK4C in AML

Simple Summary

CDK4/6 kinase inhibitors show promising results in various subtypes of AML, which has been primarily assigned to the inhibition of CDK6. To bypass therapeutic resistances and tackle the kinase-dependent, as well as kinase-independent, functions of CDK6, new CDK6 degraders have been developed. Here, we present insights into the mechanistic requirements for the efficacy of a CDK6-specific degrader in AML. We show that the presence and levels of the INK4 proteins p16^INK4A and p18^INK4C determine the extent of CDK6 degradation. Our study reveals the importance of INK4 protein levels as predictive markers for CDK6-targeted therapy in AML.

Abstract

Cyclin-dependent kinase 6 (CDK6) represents a novel therapeutic target for the treatment of certain subtypes of acute myeloid leukaemia (AML). CDK4/6 kinase inhibitors have been widely studied in many cancer types and their effects may be limited by primary and secondary resistance mechanisms. CDK4/6 degraders, which eliminate kinase-dependent and kinase-independent effects, have been suggested as an alternative therapeutic option. We show that the efficacy of the CDK6-specific protein degrader BSJ-03-123 varies among AML subtypes and depends on the low expression of the INK4 proteins p16^INK4A and p18^INK4C. INK4 protein levels are significantly elevated in KMT2A-MLLT3+ cells compared to RUNX1-RUNX1T1+ cells, contributing to the different CDK6 degradation efficacy. We demonstrate that CDK6 complexes containing p16^INK4A or p18^INK4C are protected from BSJ-mediated degradation and that INK4 levels define the proliferative response to CDK6 degradation. These findings define INK4 proteins as predictive markers for CDK6 degradation-targeted therapies in AML.

MiRNA-494-3p Regulates Bupivacaine-Induced Neurotoxicity by the CDK6-PI3K/AKT Signaling

Bupivacaine (BUP) is a long-acting amide local anesthetic that may induce strong neurotoxicity and neurological complications. In this study, we elucidate the influence of microRNA-494-3p (miR-494-3p) in BUP-induced neurotoxicity in primary mouse hippocampal neuronal cells. In this study, primary hippocampal neurons were isolated from neonatal C57BL/6 mice. The isolated neurons were treated with various doses of BUP. MTT assay was conducted to analyze neuronal viability. Gene expression measurement was done by RT-qPCR. The impact of miR-494-3p in BUP-mediated neural injury was examined using TUNEL, flow cytometry, western blotting, and ROS activity detection. The regulatory relationship between miR-494-3p and cyclin-dependent kinases 4 and 6 (CDK6) was identified using a luciferase reporter assay. BUP treatment led to neurotoxicity and miR-494-3p upregulation in primary cultured hippocampal neurons. Functionally, miR-494-3p depletion alleviated neuronal apoptosis and oxidative damage induced by BUP. We verified that miR-494-3p targeted and negatively modulated CDK6. MiR-494-3p depletion also activated PI3K/AKT signaling by elevating CDK6 expression in BUP-treated neurons. Furthermore, CDK6 knockdown or PI3K/AKT inactivation attenuated the neuroprotective role of miR-494-3p depletion. Silencing miR-494-3p exerts neuroprotective function in hippocampal neuronal cells against BUP-induced injury by the CDK6-PI3K/AKT pathway.

T Cell-Intrinsic CDK6 Is Dispensable for Anti-Viral and Anti-Tumor Responses In Vivo

The cyclin-dependent kinase 6 (CDK6) regulates the transition through the G1-phase of the cell cycle, but also acts as a transcriptional regulator. As such CDK6 regulates cell survival or cytokine secretion together with STATs, AP-1 or NF-κB. In the hematopoietic system, CDK6 regulates T cell development and promotes leukemia and lymphoma. CDK4/6 kinase inhibitors are FDA approved for treatment of breast cancer patients and have been reported to enhance T cell-mediated anti-tumor immunity. The involvement of CDK6 in T cell functions remains enigmatic. We here investigated the role of CDK6 in CD8+ T cells, using previously generated CDK6 knockout (Cdk6-/-) and kinase-dead mutant CDK6 (Cdk6K43M) knock-in mice. RNA-seq analysis indicated a role of CDK6 in T cell metabolism and interferon (IFN) signaling. To investigate whether these CDK6 functions are T cell-intrinsic, we generated a T cell-specific CDK6 knockout mouse model (Cdk6fl/fl CD4-Cre). T cell-intrinsic loss of CDK6 enhanced mitochondrial respiration in CD8+ T cells, but did not impact on cytotoxicity and production of the effector cytokines IFN-γ and TNF-α by CD8+ T cells in vitro. Loss of CDK6 in peripheral T cells did not affect tumor surveillance of MC38 tumors in vivo. Similarly, while we observed an impaired induction of early responses to type I IFN in CDK6-deficient CD8+ T cells, we failed to observe any differences in the response to LCMV infection upon T cell-intrinsic loss of CDK6 in vivo. This apparent contradiction might at least partially be explained by the reduced expression of Socs1, a negative regulator of IFN signaling, in CDK6-deficient CD8+ T cells. Therefore, our data are in line with a dual role of CDK6 in IFN signaling; while CDK6 promotes early IFN responses, it is also involved in the induction of a negative feedback loop. These data assign CDK6 a role in the fine-tuning of cytokine responses.