Announcements

1
Announcements

• Quiz in class on Thursday covers material in
  lectures and readings since April 1
• Review session Wednesday at 730p in B121
• Because Thursday is part of Passover, a makeup
  quiz will be offered in my office, Porter Biosci.
  B031, Fri. 2 pm. Notify me before Thursday
• Dont forget the web assignment
• Come and find out about pre-hospital care with
  paramedics, EMTs, firefighters and the head of
  the EMT program from Avista Hospital. Find out
  how to get your license to work in the Emergency
  Room, ambulance and/or first aid ski station.
• When Thursday, April 17th at 700 pm
• Where Porter B121

2
Leukemia and Lymphoma

• An analysis of the diseases in terms of our
  current understanding at a molecular level

3
The nature of the diseases

• Leukemias are fatal sarcomas of the white blood
  cells characterized by a marked increase in the
  number of leukocytes (white blood cells) and
  their precursors.
• Lymphomas are tumor of lymphoid tissue, which is
  largely the subset of leukocytes that is involved
  in the immune response, i.e., the lymphocytes.
• Some leukemias are lymphomas and vice versa

4
Blood is a complex connective tissue with lots of
cell types and extensive fluid matrix (the
plasma). Light micrograph of a blood smear,
showing many erythrocytes (pale pink), four kinds
of white blood cells, and some platelets.
5
In acute myelogenous leukemia the number of a
particular white cell type increases markedly
6
Some terms you simply have to learn

• Erythrocyte a red blood cell
• Lymphocyte any of several white blood cells that
  contribute to the immune response
• B-cells lymphocytes produced in the bone marrow.
  These cells make immunoglobulins (Igs)
• T-cells lymphocytes that are modified by
  developments in the thymus. There are several
  kinds of T-cells, including helper, suppressor,
  and cytotoxic T-cells.
• Thymus an important organ of the immune system,
  located in the neck, where antigens and immune
  cells meet to promote differentiation

7
Start simply by looking at red cells

• There is only one kind of erythrocyte. It is
  formed by the terminal differentiation of an
  erythroblast.
• Erythroblasts arise from the commitment and
  differentiation of a pluripotential
  hematopoietic stem cell
• This cell turns on the synthesis of hemoglobin
  and other red cell proteins, and then discards
  the nucleus
• All this differentiation occurs in bone marrow,
  and it produces about 106 cells/sec

8
Erythrocytes form by the differentiation of an
erythroblast.
9
Erythroblasts form from the differentiation of a
progenitor cell that also produces other cells
10
Electron micrographs of white blood cells that
originate from the same progenitor as
erythroblasts neutrophil, basophil, eosinophil,
and monocyte
11
A similar pathway produces lymphocytes and
related cells
12
Light micrograph of bone marrow showing one giant
megakaryocyte, which makes blood platelets, and
many smaller hematopoietic cell that are forming
various mature blood cell types. The empty
spaces are fat cells
13
All blood cells arise from one kind of
multipotent stem cell
14
There are many growth factors that are specific
for the formation of specific blood cell types

• Factor Target Cell Produced in Receptor
• Erythropoietin CFC-E kidney cells cytokine
• IL-3 stem cells T cells cytokine
• GMCSF GM progen. T cells, fibrob. Cytokine
• G-CSF GM progen. Macroph. Fibro. Cytokine
• M-CSF GM progen. Fibro. Macro. RTKs
• Steel factor hemopoiet. Stroma of RTKs
• stem cells marrow

15
Many factors govern the number of blood cells of
each type
16
Normal cell renewal can go wrong
17
Failures of these kinds in hematopoietic cells
give rise to leukemias

• Excessive division without appropriate
  differentiation of bone marrow cells produces
  myelogenous (marrow related) leukemias
• Excessive divisions of leukocytes already
  destined to become lymphocytes produces a
  lymphoma
• Many of these diseases can be distinguished based
  on symptoms and the characteristics of the cells
  that are over-produced

18
Ways to distinguish leukemias have developed over
time

• Initial distinctions were based in part on
  microscopy lymphocytic leukemia vs. granulocytic
  leukemia
• Additional distinctions were based on the
  severity of the disease at diagnosis and on its
  rate of progression acute lymphocytic leukemia
  (abbreviated ALL) vs. chronic myeologenous
  leukemia (CML), etc.

19
The distinctions between leukemias are now made
at a molecular level

• The surfaces leukocytes are key to their function
  and therefore serve as an excellent source of
  distinguishing markers
• Most surface distinctions have been made by
  monoclonal antibodies that identify specific cell
  surface receptors CD4, CD8, etc. Prevalence of
  one or more of these is characteristic of
  different stages of lymphocyte development and
  defines the kind of leukemia under study

20
Cancerous transformations at different stages in
blood cell formation produce different phenotypes
for the resulting neoplasm

• Myelogenous produced in the bone marrow
• Acute short or sharp having a short course
• Chronic long or continued not acute
• A lymphocytic leukemia could be called a
  lymphoma. The terminology is based in part on
  history and is not strictly rational

21
Leukemias and lymphomas result from changes at
many levels of cell cycle regulation
22
Detailed studies of the chromosomes in various
leukemias have revealed characteristic
chromosomal abnormalities

• In 1960, cytogeneticists who studied the
  chromosomes of patients with Chronic Myelogenous
  Leukemia (CML) found a translocation between
  chromosomes 9 and 22 in about 95 of patients
• Unusual chromosomes were formed by the
  translocation. The smaller of these was called
  the Philadelphia chromosome (Ph)

23
A primer on chromosome notation

• Each autosomal chromosome is numbered, the
  biggest is called 1. Sex chrs. come last
• When the centromere is not at an end, one can
  distinguish a long arm (q) and a short (p)
• The position of bands (e.g., regions of strong
  Giemsa staining) are named sequentially out from
  the centromere in blocks 1, 2, 3, and they are
  subdivided by 23, 24, etc., even 23.2

24
Naming and mapping translocations

• Translocations (t) are named by the chromosomes
  from which and to which DNA is moved (e.g.,
  t(9,22)) and by the position of the breakpoint on
  each chromosome (e.g., (q32q11).
• The Ph. chromosome is formed by t(922)(q32q11)
• A translocation common in Burkitts lymphoma is
  t(814)(q24q32)

25
Diagrams of Chrs. 9 and 22, showing G-bandings
and the morphologies of the chromosomes after
translocation 9 is now bigger (9q), while 22
(the Ph) is now shorter (22q-). Positions of the
breakpoints can be mapped.
26
Some such translocations turn out to be causative
for cancer

• While the translocations were initially seen as a
  curiosity, more detailed knowledge of the genes
  that lie at the breakpoints has clarified the
  importance of these genotypes for the phenotypes
  of the cancers in question
• The translocations bring proto-oncogenes under
  strong and inappropriate promotors or make fusion
  proteins that have extra functions

27
Translocations can alter gene expression and/or
function

• The formation of a Ph. chromosome moves the gene
  for a protein tyrosine kinase involved in cell
  cycle control (c-abl at 9q34) into a region
  called the breakpoint cluster region (bcr) on
  22q11, producing a fusion protein that is a
  hyper-active and promiscuous protein tyrosine
  kinase. This helps to drive excess cell
  division.

28
(No Transcript)
29
Significance of translocation

• The mutant cells now produce active protein
  tyrosine kinase regardless of the signals coming
  in (or not) from growth factors
• The lymphocytes are now independent of the
  usually essential growth factors IL-3 and GMCSF,
  so proliferation is uncontrolled
• The translocations make an oncogene

30
Many B-cell lymphomas have translocations that
move a proto-oncogene into the immunoglobulin
locus

• Burkitts lymphoma moves the c-myc proto-oncogene
  from 8q24 (where it encodes a transcription
  factor that is a target for the ras-dependent
  growth factor pathway) to 14q32, which is the
  locus for an immunoglobulin heavy chain. In this
  new position, it is near Ig enhancers and becomes
  over expressed.

31
The immunoglobulin loci are often modified in
B-cell lymphomas

• 14q32 received a translocation in 60 of all
  B-cell-related non-Hodgkin lymphomas
• In Follicular lymphomas, this locus receives the
  Bcl2 gene from 18q21 where it is normally
  involved in apoptosis
• Philadelphia chromosomes are found in 10 of all
  acute lyphocytic leukemias and 5 of all acute
  myelogenous leukemias

32
Why the immunoglobulin genes?

• During B-cell differentiation, the genomic DNA is
  rearranged to allow each clone of B-cells to make
  one and only one Ig molecule. Usually this
  rearrangement involves adjacent regions of DNA
  (different variable or V and D regions and the
  joining regions are shuffled then fused with
  the constant region).
• Probably this normal process puts the cell at
  risk for a totally illegitimate process that ends
  up as a translocation.
• Probably lots of genes sneak into the Ig locus
  but only proto-oncogenes get noticed through the
  development of a cancerous phenotype

33
This hypothesis is supported by the
translocations seen in T-cell leukemias

• T-cells dont make Igs, they make T-cell
  Receptors which are highly variable membrane
  proteins that function like Igs
• In T-cell lymphomas, proto-oncogenes like c-myc,
  are translocated into the gene for the alpha
  chain of the T-cell receptor, so it is the same
  story

34
Translocation is not the whole story

• Burkitts lymphoma also involves infection by the
  Epstein-Barr virus, though just why is not known
• Some leukemias show amplification of a specific
  proto-oncogene by inappropriate DNA replication

35
Chromosomes are stained red, the myc gene is
yellow from in situ hybridization. Upper
karyotype shows many minute myc-containing
chromosomes the lower shows a few amplified loci.
36
Progression from chronic to acute forms of
leukemia can be accompanied by additional
genotype changes

• In CML, one Ph. chromosome appears early in the
  disease. With acceleration of the disease in
  blast phase, often get either a second Ph or
  trisomy of chr. 8
• In folicular lymphomas, the transition to acute
  is accompanied by additional t(814) changes that
  amplify myc

37
Summary

• Many leukemias form in association with genetic
  changes that transform proto-oncogenes into
  oncogenes by over expression or mutation
• The progression of leukemias is accompanied by
  additional genotypic changes that accelerate cell
  growth
• Agents such as viruses can contribute to these
  processes in ways that are not yet well worked out