Human RBL2 adenoviral particles

Anthracycline chemotherapy induces heart failure in some cancer patients. Previous studies have shown that the anthracycline doxorubicin (DOX) induces cardiotoxicity via activation of cyclin-dependent kinase 2 (CDK2). Here, researchers found that loss of endogenous Rbl2 increases basal CDK2 activity in mouse hearts. Mice lacking Rbl2 were more sensitive to DOX-induced cardiotoxicity, as evidenced by rapid deterioration of cardiac function and reduced heart weight. Disruption of Rbl2 exacerbated DOX-induced mitochondrial damage and cardiomyocyte apoptosis. Mechanistically, Rbl2 deficiency enhanced CDK2-dependent forkhead box O1 (FOXO1) activation, leading to upregulation of the pro-apoptotic protein Bim. Inhibition of CDK2 desensitized Rbl2-depleted cardiomyocytes to DOX. In wild-type cardiomyocytes, DOX exposure induced Rbl2 expression in a FOXO1-dependent manner. Importantly, the rs17800727 G allele of the human RBL2 gene is associated with reduced anthracycline cardiotoxicity in childhood cancer survivors.

In the presence of DOX, knockdown of Rbl2 increased the protein levels of phosphorylated CDK2 (T160), Bim, and cleaved PARP (Figure 1A), indicating increased CDK2 activation and apoptosis. Treatment with the CDK inhibitor roscovitine abolished the upregulation of phospho-CDK2 (T160), Bim, and cleaved PARP caused by Rbl2 depletion (Figure 1A). Neonatal rat cardiomyocytes (NRCMs) were infected with green fluorescent protein adenovirus (AdGFP) or human RBL2 adenovirus (AdRBL2) and treated with DOX for 24 hours. Overexpression of Rbl2 reduced the levels of phosphorylated CDK2 (T160) and Bim after treatment with DOX (Figure 1B), indicating that Rbl2 inhibits CDK2-dependent Bim expression. Previous studies have shown that CDK2 phosphorylates FOXO1 at S249, thereby activating FOXO1-mediated Bim transcription. Here, depletion of Rbl2 significantly enhanced DOX-induced FOXO1 phosphorylation at S249 (Figure 1C). Moreover, pretreatment with the FOXO1 inhibitor AS1842856 reduced Bim levels and abolished Bim upregulation caused by Rbl2 depletion (Figure 1D). These results suggest that Rbl2 deficiency increases DOX sensitivity by uncontrolled activation of the CDK2-FOXO1-Bim axis.

Figure 1. Rbl2 Depletion Enhanced DOX-Induced CDK2-FOXO1-Bim Activation. (Xia P, et al., 2023)