Chapter 16 Essential Concepts in Molecular Pathology Companion site for Molecular Pathology Author: William B. Coleman and Gregory J. Tsongalis

Companion site for Molecular Pathology Copyright © 2009 by Academic Press. All rights reserved. 2 FIGURE 16.1 Hematopoietic development. The upper panel shows stages of hematopoiesis in the mouse. Hematopoietic stem cells (HSCs) are derived from the ventral mesoderm, and sequential sites of hematopoiesis include the yolk sac, the aorta-gonad- mesonephros (AGM) region, the fetal liver, placenta, and bone marrow. The types of cells produced at each site are illustrated in the middle panel. The main function of primitive hematopoiesis, which occurs in the yolk sac, is to produce red blood cells. The relative contribution of HSCs produced in the AGM region and the placenta to the final pool of adult HSCs remains unknown. Definitive hematopoiesis involves the colonization of the fetal liver, thymus, spleen, and bone marrow. In definitive hematopoiesis, long-term HSCs produce short-term HSCs, which in turn give rise to common myeloid progenitors (CMPs) and common lymphoid progenitors (CLPs). CMPs produce megakaryocyte/erythroid progenitors (MEPs) and granulocyte/macrophage progenitors (GMPs). CLPs produce B and T lymphocytes. The lower panel shows transcription factors that regulate hematopoiesis in mammals. The stages at which hematopoietic development is blocked in the absence of a given factor, as determined through gene knockout, are indicated by red loops. The factors in red are associated with oncogenesis; those in black have not yet been found mutated in hematologic malignancies. Among the genes required for HSC production, survival, or self-renewal are MLL, Runx1, TEL/EV6, SCL/tal1, and LMO2. These genes account in toto for the majority of known leukemia-associated translocations in patients. Reproduced with permission from Orkin SH and Zon LI, SnapShot: Hematopoiesis Cell 2008;132:172.e1.

Companion site for Molecular Pathology Copyright © 2009 by Academic Press. All rights reserved. 3 FIGURE 16.2 Stem cell niche in adult bone marrow. HSCs are found in the osteoblast niche adjacent to osteoblasts that are under the regulation of bone morphogenetic protein (BMP). Pathways involving Notch, wnt, and PGE-2 stimulate HSC self-renewal. HSCs are also found adjacent to blood vessels (the vascular niche). The chemokine CXCL12 regulates the migration of HSCs from the circulation to the bone marrow. The osteoblast and vascular niches in vivo lie in close proximity or may be interdigitated. The marrow space also contains stromal cells that support hematopoiesis including the production of cytokines, such as c-Kit ligand, that stimulate stem cells and progenitors. Other cytokines, including interleukins, thrombopoietin, and erythropoietin, also influence progenitor function and survival. Reproduced with permission from Orkin SH and Zon L?I, Cell 2008;132:631–644.

Companion site for Molecular Pathology Copyright © 2009 by Academic Press. All rights reserved. 4 FIGURE 16.3 Signal transduction pathways involved in leukemia. The drawing on the left shows signaling of a receptor tyrosine kinase (RTK) through Ras. Ligand binding causes phosphorylation of Grb-2 by the RTK and formation of a Grb-2/SOS complex. Interaction of Grb-2/SOS with farnesylated (F) Ras-GDP causes conversion to active Ras-GTP, which in turn phosphorylates Rac, Raf, and PI3K leading to stimulation of their respective pathways. The drawing on the right shows the JAK/STAT pathway. Ligand binding causes RTK phosphorylation of JAK, which may then activate the Ras pathway and phosphorylate STATs. The STATs form homodimers or heterodimers with other STATs and translocate to the nucleus where they activate transcription of specific target genes.

Companion site for Molecular Pathology Copyright © 2009 by Academic Press. All rights reserved. 5 FIGURE 16.4 Targeting signaling pathways of BCR-ABL. The BCR-ABL onco protein chronically activates many different downstream signaling pathways to confer malignant transformation in hematopoietic cells. For example, efficient activation of PI3K, Ras, and reactive oxygen species (ROS) requires autophosphorylation on Tyr177, a Grb-2 binding site in BCR-ABL. Also, activation of Src family tyrosine kinases have been implicated in the BCR-ABL-related disease process. A selection of some inhibitors and pathways discussed in the text is illustrated. Reproduced with permission from Walz C and Sattler M, Critical Reviews in Oncology/Hematology 2006;57:145–164.

Companion site for Molecular Pathology Copyright © 2009 by Academic Press. All rights reserved. 6 FIGURE 16.5 NOTCH signaling. Interaction of NOTCH and delta serrate ligand (DSL) stimulates proteolytic cleavage of NOTCH by metalloproteases and γ- secretase. This leads to the release of the intracellular ICN domain, which translocates to the nucleus where it interacts with the DNA binding protein CSL, displaces corepressors and recruits co-activators (MAM1), thereby converting CSL from a repressor to an activator of gene expression. Reproduced with permission from Armstrong SA and Look AT, J. Clin. Oncol. 2005;23:6306.

Companion site for Molecular Pathology Copyright © 2009 by Academic Press. All rights reserved. 7 FIGURE 16.6 Reed-Sternberg cell. The figure shows the typical characteristics of the Reed-Sternberg cell: large size (20–50 micrometers), amphophilic and homogeneous cytoplasm, and two mirror-image nuclei (owl eyes) with one eosinophilic nucleolus in each nucleus. Reed- Sternberg cells only occupy a small portion of the tumor mass. Reproduced with permission from a website maintained by the Department of Pathology, Stanford University (