Tumor suppressor protein p53 regulates megakaryocytic polyploidization and apoptosis.

The molecular mechanisms underlying differentiation of hematopoietic stem cells into megakaryocytes are poorly understood. Tumor suppressor protein p53 can act as a transcription factor affecting both cell cycle control and apoptosis, and we have previously shown that p53 is activated during terminal megakaryocytic (Mk) differentiation of the CHRF-288-11 (CHRF) cell line. Here, we use RNA interference to reduce p53 expression in CHRF cells and show that reduced p53 activity leads to a greater fraction of polyploid cells, higher mean and maximum ploidy, accelerated DNA synthesis, and delayed apoptosis and cell death upon phorbol 12-myristate 13-acetate-induced Mk differentiation.

Gene Ontology-driven transcriptional analysis of CD34+ cell-initiated megakaryocytic cultures identifies new transcriptional regulators of megakaryopoiesis.

Differentiation of hematopoietic stem and progenitor cells is an intricate process controlled in large part at the level of transcription. While some key megakaryocytic transcription factors have been identified, the complete network of megakaryocytic transcriptional control is poorly understood. Using global gene expression microarray analysis, Gene Ontology-based functional annotations, and a novel interlineage comparison with parallel, isogenic granulocytic cultures as a negative control, we closely examined the mRNA level of transcriptional regulators in megakaryocytes derived from human mobilized peripheral blood CD34(+) hematopoietic cells.

A systems-biology analysis of isogenic megakaryocytic and granulocytic cultures identifies new molecular components of megakaryocytic apoptosis.

Background: The differentiation of hematopoietic stem cells into platelet-forming megakaryocytes is of fundamental importance to hemostasis. Constitutive apoptosis is an integral, yet poorly understood, facet of megakaryocytic (Mk) differentiation. Understanding Mk apoptosis could lead to advances in the treatment of Mk and platelet disorders.

Comparative, genome-scale transcriptional analysis of CHRF-288-11 and primary human megakaryocytic cell cultures provides novel insights into lineage-specific differentiation.

Objectives: Little is known about the transcriptional events underlying megakaryocytic (Mk) differentiation. We sought to identify genes and pathways previously unassociated with megakaryopoiesis and to evaluate the CHRF-288-11 (CHRF) megakaryoblastic cell line as a model system for investigating megakaryopoiesis.

Methods: Using DNA microarrays, Q-RT-PCR, and protein-level assays, we compared the dynamic gene expression pattern of phorbol ester-induced differentiation of CHRF cells to cytokine-induced Mk differentiation of human mobilized peripheral blood CD34(+) cells.

Deregulated CDC25A expression promotes mammary tumorigenesis with genomic instability.

Checkpoint pathways help cells maintain genomic integrity, delaying cell cycle progression in response to various risks of fidelity, such as genotoxic stresses, compromised DNA replication, and impaired spindle control. Cancer cells frequently exhibit genomic instability, and recent studies showed that checkpoint pathways are likely to serve as a tumor-suppressive barrier in vivo. The cell cycle-promoting phosphatase CDC25A is an activator of cyclin-dependent kinases and one of the downstream targets for the CHK1-mediated checkpoint pathway.

Nicotinamide (vitamin B3) increases the polyploidisation and proplatelet formation of cultured primary human megakaryocytes.

Megakaryocytic (Mk) cell maturation involves polyploidisation, and the number of platelets produced increases with Mk DNA content. Ploidy levels in cultured human MK cells are much lower than those observed in vivo. This study demonstrated that adding the water-soluble vitamin nicotinamide (NIC) to mobilised peripheral blood CD34+ cells cultured with thrombopoietin (Tpo) more than doubled the percentage of high-ploidy (> or = 8N) MK cells.