Osteoblasts and The Hematopoietic Microenvironment

Cells of the bone marrow are chiefly dedicated to two processes; the production of blood, and the production of bone that houses the hematopoietic organ. The majority of our understanding of these processes comes from data focused on one of these functions. Yet, in vivo the processes are intermixed. Our recent data demonstrate that human osteoblast-like cells have important accessory roles in hematopoiesis. These data include the demonstration that human osteoblast-like cells; support the growth of primitive human hematopoietic progenitors (CD34⁺ cells) in short and long term cultures and, synthesize multiple cytokines believed to regulate hematopoiesis. Based upon anatomic and developmental findings characterizing hematopoietic cells in close approximation with endosteal cells, and these findings, we hypothesize that osteoblasts play a critical role in hematopoietic cells development in vivo.     

Tumor-necrosis factor induces cell cycle arrest in multipotential hematopoietic stem cells: a possible radioprotective mechanism

Tumor-necrosis factor (TNF) and interleukin-1 (IL-1) have been shown to confer protection of hematopoiesis in mice challenged with radiation. Herein, a series of experiments designed to elucidate the underlying mechanism is presented. After TNF administration, colony-stimulating activity, but no IL-1 activity, was detectable in mouse plasma. In endogenous CFU-S assays, TNF enhanced the survival of multipotential progenitors when administered before, but not after, irradiation. In experiments with fractionated irradiation, the radioprotective effect of TNF was distinctly different from that of IL-1. In vivo and in vitro thymidine suicide assays demonstrated that TNF wholly or partially abolished cell cycling of the CFU-S hematopoietic compartment. These data imply that TNF may inhibit the cell cycle in hematopoietic progenitor cell populations.     

Gatekeeper function of the RUNX1 transcription factor in acute leukemia

The RUNX1 gene encodes the alpha subunit of the core binding factor (CBF) and is a common target of genetic mutations in acute leukemia. We propose that RUNX1 is a gatekeeper gene, the disruption of which leads to the exodus of a subset of hematopoietic progenitors with increased self-renewal potential from the normal environmental controls of homeostasis. This pool of "escaped" cells is the target of secondary mutations, accumulating over time to induce the aggressive manifestation of acute leukemia. Evidence from patient and animal studies supports the concept that RUNX1 mutations are the initiating event in different leukemia subtypes, but also suggests that diverse mechanisms are used to subvert RUNX1 function. One common result is the inhibition of differentiation-but its effect impinges on different lineages and stages of differentiation, depending on the mutation or fusion partner. A number of different approaches have led to the identification of secondary events that lead to the overt acute phase; however, the majority is unknown. Finally, the concept of the "leukemia stem cell" and its therapeutic importance is discussed in light of the RUNX1 gatekeeper function.     

The effect of nerve growth factor and antibodies to nerve growth factor on ethylnitrosourea carcinogenesis in mice

Summary The specific induction of neural tumors by the carcinogen, ethylnitrosourea (ENU), can be enhanced by reducing the in vivo nerve growth factor (NGF) levels in mice using IgG directed against the biologically active subunit of NGF (anti-NGF). This effect is reversible, confirming that the altered endogenous NGF levels do return to normal following injection with anit-NGF. Correspondingly, no neural tumors were observed when in vivo NGF levels were elevated by administering exogenous NGF with ENU. The higher physiological levels of NGF in control mice when compared to control rats might explain why fetal administration of ENU to rats results in a greater percentage of neural tumors. This would suggest that the long studied maturation effect that NGF has on developing neural cells of the peripheral nervous system may also influence neural oncogenesis.Submitted in partial fulfillment of PhD at Zoology Department, University of Texas at Austin, TX, USAThis research was supported by NIH 5 T01 GM 00337-15 and CA 09182-01 for S.A.V. and NINDS grants NS 14034 and NS15324, and Welch grant H 698 to J.R.P.     

Genetic lesions in MYC and STAT3 drive oncogenic transcription factor overexpression in plasmablastic lymphoma

The mutational profile of plasmablastic lymphoma has not been described. We performed a targeted, exonic next-generation sequencing analysis of 30 plasmablastic lymphoma cases with a Bcell lymphoma-dedicated panel and fluorescence in situ hybridization for the detection of MYC rearrangements. Complete phenotyping of the neoplastic and microenvironmental cell populations was also performed. We identified an enrichment in recurrent genetic events in MYC (69% with MYC translocation or amplification and three cases with missense point mutations), PRDM1/Blimp1 and STAT3 mutations. These gene mutations were more frequent in Epstein-Barr virus (EBV)-positive disease. Other genetic events included mutations in BRAF, EP300, BCR (CD79A and CD79B), NOTCH pathway (NOTCH2, NOTCH1 and SGK1) and MYD88pL265P. Immunohistochemical analysis showed consistent MYC expression, which was higher in cases with MYC rearrangements, together with phospho-STAT3 (Tyr705) overexpression in cases with STAT3 SH2 domain mutations. Microenvironmental cell populations were heterogeneous and unrelated to EBV, with enrichment of tumor-associated macrophages (TAM) and PD1-positive T cells. PD-L1 was expressed in all cases in the TAM population but only in the neoplastic cells in five cases (4 of 14 EBV-positive cases). HLA expression was absent in the majority of cases of plasmablastic lymphoma. In summary, the mutational profile of plasmablastic lymphoma is heterogeneous and related to EBV infection. Genetic events in MYC, STAT3 and PRDM1/Blimp1 are more frequent in EBV-positive disease. An enrichment in TAM and PD1 reactive T lymphocytes is found in the microenvironment of plasmablastic lymphoma and a fraction of the neoplastic cells express PD-L1.