The tumor suppressor p15Ink4b regulates the differentiation and maturation of conventional dendritic cells

Abstract

The tumor suppressor p15Ink4b is frequently inactivated by methylation in acute myeloid leukemia and premalignant myeloid disorders. Dendritic cells (DCs) as potent APCs play critical regulatory roles in antileukemic immune responses. In the present study, we investigated whether p15Ink4b can function as modulator of DC development. The expression of p15Ink4b is induced strongly during differentiation and activation of DCs, and its loss resulted in significant quantitative and qualitative impairments of conventional DC (cDC) development. Accordingly, ex vivo-generated BMderived DCs from p15Ink4b-knockout mice express significantly decreased levels of the antigen-presenting (MHC II) and costimulatory (CD80 and CD86) molecules and have impaired immunostimulatory functions, such as antigen uptake and T-cell stimulation. Reexpression of p15Ink4b in progenitors restored these defects, and confirmed a positive role for p15Ink4b during cDC differentiation and maturation. Furthermore, we have shown herein that p15Ink4b expression increases phosphorylation of Erk1/Erk2 kinases, which leads to an elevated activity of the PU.1 transcription factor. In conclusion, our results establish p15Ink4b as an important modulator of cDC development and implicate a novel function for this tumor suppressor in the regulation of adaptive immune responses. (Blood. 2012;119(21):5005-5015) IntroductionIn acute myeloid leukemia (AML), one of the most common epigenetic abnormalities observed in patients is the transcriptional silencing of p15INK4b (Cdkn2b) by DNA hypermethylation. 1,2 Increased DNA methylation of the p15INK4b gene regulatory sequences has been reported in up to 80% of all patients suffering from AML, and in a high proportion of patients with other hematologic disorders, including myelodysplastic syndrome (MDS), and myeloproliferative neoplasms. 3,4 Clinical observations have established a strong correlation between the methylation levels of p15INK4b and poor prognosis in patients. Hypermethylation also provides a biomarker for the subsequent transformation and progression of the disease to a more aggressive phenotype. 3 The tumor-suppressor function of p15Ink4b for myeloid diseases was confirmed experimentally in an animal model with myeloidspecific deletion of the gene. These mice suffer from a mild form of myeloproliferative neoplasm resembling chronic myelomonocytic leukemia and are strongly predisposed to retrovirus-induced AML. 5 p15INK4b is a cyclin-dependent kinase inhibitor (CDKI) that binds and inhibits the activity of 2 cyclin-dependent kinases, CDK4 and CDK6. This inhibition leads to cell-cycle arrest during the early and mid-G 1 phase. 6 In accordance with its cell cycleinhibitory function, the expression levels of p15Ink4b are reported to be increased during the late maturation stages of myeloid progenitors associated with terminal differentiation into macrophages. 7 p15Ink4b has also been shown to play a role during early stages of hematopoiesis independently from its cell cycleinhibitory function. 8 During ea...

The role of tumor suppressor p15Ink4b in the regulation of hematopoietic progenitor cell fate

“…33 Interestingly, ERK1/2 was also observed to be an important effector downstream of p15Ink4b in the development of dendritic cells. 36 As shown here, the downstream effects of this signaling cause decreases in the expression of GATA-2 and Pu.1 and increases in GATA-1 as well as EPOR. p15Ink4b-induced signaling may impact a replacement of GATA-2 with GATA-1 at some promoters, a process known as the ‘GATA switch'.…”

Concise Review: Erythroid Versus Myeloid Lineage Commitment: Regulating the Master Regulators

“…Intriguingly, introduction of p15Ink4b into multipotential progenitors rendered cells them more permissive to erythroid commitment and less permissive to myeloid commitment as shown by alterations in the ability to form erythroid and myeloid colonies in semisolid media. Although p15Ink4b was originally discovered to be a cyclin‐dependent kinase inhibitor, its function in cell fate appears to depend upon its ability to activate a signaling pathway involving Erk phosphorylation [62, 63]. In addition, the introduction of the gene in EML cells, a stem‐cell like line, resulted in a reduction in the levels of GATA‐2 protein.…”