Activation of Protein Kinase Cδ by All-trans-retinoic Acid

All-trans-retinoic acid (RA) is a potent inhibitor of leukemia cell proliferation and induces differentiation of acute promyelocytic leukemia cells in vitro and in vivo. For RA to induce its biological effects in target cells, binding to specific retinoic acid nuclear receptors is required. The resulting complexes bind to RA-responsive elements (RAREs) in the promoters of RA-inducible genes to initiate gene transcription and to generate protein products that mediate the biological effects of RA. In this report, we provide evidence that a member of the protein kinase C (PKC) family of proteins, PKC delta, is activated during RA treatment of the NB-4 and HL-60 acute myeloid leukemia cell lines as well as the MCF-7 breast cancer cell line. Such RA-dependent phosphorylation was also observed in primary acute promyelocytic leukemia cells and resulted in activation of the kinase domain of PKC delta. In studies aimed at understanding the functional relevance of PKC delta in the induction of RA responses, we found that pharmacological inhibition of PKC delta (but not of other PKC isoforms) diminished RA-dependent gene transcription via RAREs. On the other hand, overexpression of a constitutively active form of the kinase strongly enhanced RA-dependent gene transcription via RAREs. Gel shift assays and chromatin immunoprecipitation studies demonstrated that PKC delta associated with retinoic acid receptor-alpha and was present in an RA-inducible protein complex that bound to RAREs. Pharmacological inhibition of PKC delta activity abrogated the induction of cell differentiation and growth inhibition of NB-4 blast cells, demonstrating that its function is required for such effects. Altogether, our data provide strong evidence that PKC delta is activated in an RA-dependent manner and plays a critical role in the generation of the biological effects of RA in malignant cells

Prognostic Testing and Treatment Patterns in Chronic Lymphocytic Leukemia in the Era of Novel Targeted Therapies: Results From the informCLL Registry.

INTRODUCTION: The therapeutic landscape for chronic lymphocytic leukemia (CLL) has significantly shifted with the approval of novel agents. Understanding current prognostic testing and treatment practices in this new era is critical. Beginning enrollment in 2015, informCLL is the first United States-based real-world, prospective, observational registry that initiated enrollment after approval of novel agents. PATIENTS AND METHODS: Eligible patients were age ≥ 18 years, started CLL treatment within 30 days of enrollment, and provided consent. For this planned interim analysis, treatments were classified into 5 groups: ibrutinib, chemoimmunotherapy, chemotherapy, immunotherapy, and other novel agents. RESULTS: Frequency of prognostic testing and treatment patterns are reported among 840 patients (459 previously untreated; 381 relapsed/refractory), enrolled largely (96%) from community practice settings. Testing for chromosomal abnormalities by fluorescence in situ hybridization, TP53 mutation, or IGHV mutation status occurred infrequently among all patients (31%, 11%, and 11%, respectively). Chemoimmunotherapy was the most common treatment in previously untreated patients (42%), whereas ibrutinib was the most common treatment among relapsed/refractory patients (51%). Of patients who tested positive for del(17p) or TP53 mutation, 34% and 26% received chemoimmunotherapy, respectively. Among patients who did not have fluorescence in situ hybridization or TP53 mutation testing prior to enrollment, 33% and 32% received chemoimmunotherapy, respectively. CONCLUSION: Our findings indicate that prognostic testing rates were poor, and approximately one-third of high-risk patients (del[17p] and TP53) received chemoimmunotherapy, which is not aligned with current CLL treatment recommendations. This represents an opportunity to educate and alert health care professionals about the necessity of prognostic testing to guide optimal CLL treatment decisions