Summary Activation of p53 by DNA damage results in either cell cycle arrest, allowing DNA repair and cell survival, or induction of apoptosis. As these opposite outcomes are both mediated by p53 stabilization, additional mechanisms to determine this decision must exist. Here we show that glycogen synthase kinase-3 (GSK-3) is required for the p53-mediated induction of the pro-apoptotic BH3 only-protein PUMA, an essential mediator of p53-induced apoptosis. Inhibition of GSK-3 protected from cell death induced by DNA damage and promoted increased long-term cell survival. We demonstrate that GSK-3 phosphorylates serine 86 of the p53-acetyltransferase Tip60. A Tip60S86A mutant was less active to induce p53 K120 acetylation, Histone 4 acetylation and expression of PUMA. Our data suggest that GSK-3 mediated Tip60S86-phosphorylation provides a link between PI3K signaling and the choice for or against apoptosis induction by p53.

Chimeric antigen receptor (CAR) T cell therapy has transformed the care of refractory B cell malignancies and holds tremendous promise for many aggressive tumors. Despite overwhelming scientific, clinical, and public interest in this rapidly expanding field, fundamental inquiries into CAR T cell mechanistic functioning are still in their infancy. Because CAR T cells are manufactured from donor T lymphocytes, and because CARs incorporate well-characterized T cell signaling components, it has largely been assumed that CARs signal analogously to canonical T cell receptors (TCRs). However, recent studies demonstrate that many aspects of CAR signaling are unique, distinct from endogenous TCR signaling, and potentially even distinct among various CAR constructs. Thus, rigorous and comprehensive proteomic investigations are required for rational engineering of improved CARs. Here, we review what is known about proximal CAR signaling in T cells, compare it to conventional TCR signaling, and outline unmet challenges to improving CAR T cell therapy.

Checkpoint kinase 1 (CHK1) is critical for intrinsic cell cycle control and coordination of cell cycle progression in response to DNA damage. Despite its essential function, CHK1 has been identified as a target to kill cancer cells and studies using Chk1 haploinsufficient mice initially suggested a role as tumor suppressor. Here, we report on the key role of CHK1 in normal B-cell development, lymphomagenesis and cell survival. Chemical CHK1 inhibition induces BCL2-regulated apoptosis in primary as well as malignant B-cells and CHK1 expression levels control the timing of lymphomagenesis in mice. Moreover, total ablation of Chk1 in B-cells arrests their development at the pro-B cell stage, a block that, surprisingly, cannot be overcome by inhibition of mitochondrial apoptosis, as cell cycle arrest is initiated as an alternative fate to limit the spread of damaged DNA. Our findings define CHK1 as essential in B-cell development and potent target to treat blood cancer.

Precursor B lymphocytes expand upon expression of a pre-B cell receptor (pre-BCR), but then transit into a resting state in which immunoglobulin light chain gene recombination is initiated. This bi-phasic sequence is orchestrated by the IL-7 receptor (IL-7R) and pre-BCR signaling, respectively, but little is known about microRNAs fine-tuning these events. Here, we show that pre-B cells lacking miR-15 family functions exhibit prolonged proliferation due to aberrant expression of the target genes cyclin E1 and D3. As a consequence, they fail to trigger the transcriptional reprogramming normally accompanying their differentiation, resulting in a developmental block at the pre-B cell stage. Intriguingly, our data indicate that the miR-15 family is suppressed by both IL-7R and pre-BCR signaling, suggesting it is actively integrated into the regulatory circuits of developing B cells. These findings identify the miR-15 family as a novel element required to promote the switch from pre-B cell proliferation to differentiation.