Haematologica 2003 - Supplements

Barlogie B, Shaughnessy J, Jr. Global gene expression profiling
of multiple myeloma, monoclonal gammopathy of undetermined
significance, and normal bone marrow plasma cells. Blood.
2002;99:1745-1757
P1.2
IG TRANSLOCATIONS, CYCLIN D DYSREGULATION,
AND OTHER GENETIC EVENTS IN MULTIPLE
MYELOMA
M. Kuehl 4 , C. Cultraro 4 , A. Dib 4 , A. Gabrea 4 , M. Martelli 4 , L.
Brents 4 , A. Zingone 4 , J. Shaughnessy 1 , J. Sawyer 1 , B.
Barlogie 1 , R. Fonseca 2 , M. Chesi 3 , P.L. Bergsagel 3
1. University of Arkansas Medical Sciences; 2 Mayo Clinic; 3.
Cornell Medical School; 4. Genetics Dept., NCI, Naval Hospital,
Bldg 8, Rm 5101, Bethesda, MD 20889-5105 Tel: (301-435-5421,
Fax: (301) 496-0047, Email: wmk@helix.nih.gov
MM is post-germinal center tumor of bone marrow
plasmablasts/plasma cells. Germinal center B cells modify DNA
by sequential rounds of somatic hypermutation and antigen
selection, and IgH switch recombination. Post-germinal center B
cells can generate plasmablasts (PB) that migrate to the bone
marrow (BM), where stromal cells enable terminal differentiation
into long-lived plasma cells (PC). MM, a low proliferative tumor
that corresponds to long-lived PB/PC, often is preceded by a premalignant
MGUS tumor, and sometimes progresses to
extramedullary MM. Virtually all human MM cell lines (HMCL)
come from extramedullary MM, including primary PC leukemia
that occurs without apparent intramedullary MM.
Ig translocations: frequent and often early events in the
pathogenesis of MM. Ig translocations dysregulate oncogenes by
juxtaposing them near one of the strong Ig enhancers.
Translocations usually involve the IgH locus, whereas the Igλ
locus is involved infrequently, and the Igκ locus rarely. The
prevalence of IgH translocations appears to be related to the stage
of the disease: about 50% in MGUS, 55-70% in intramedullary
MM, >80% in extramedullary MM, and more than 90% in
HMCL. Primary Ig translocations occur in germinal center B
cells, usually a result of errors in IgH switch recombination, or
less often somatic hypermutation.
Secondary (Ig) translocations occur during tumor progression.
Secondary translocations are mediated by different mechanisms
than most primary translocations, since B cell specific DNA
modification processes are inactive in normal or malignant
PB/PC. Features that often distinguish secondary translocations
include: breakpoints not within or near IgH switch or V(D)J
sequences, complex and unbalanced translocations or insertions,
heterogeneity within a tumor, and sometimes lack of
involvement of an Ig enhancer. The dysregulation of c-, N-, or L-
MYC, which usually occurs as a very late progression event,
provides a paradigm for secondary translocations. The increased
prevalence of Ig translocations at later stages of disease and in
HMCL probably is explained partly by secondary Ig
translocations but also by selective progression of tumors with Ig
translocations.
Different oncogenes for primary and secondary translocations.
Four recurrent chromosomal loci (oncogenes) are involved in
primary translocations: 11q13 (cyclin D1); 6p21 (cyclin D3);
4p16 (MMSET; FGFR3); 16q23 (c-maf); and these account for
IgH translocations in about 40% of tumors. Loci involved in
secondary translocations include: 8q24 (c-myc), 2p23 (N-myc),
20q12 (maf B), and 6p25 (MUM-1/IRF-4), but these probably
account for IgH translocations in only 5% of tumors. Nonrecurrent
loci are involved in IgH translocations in nearly 20% of
tumors, but the fraction of primary vs secondary translocations is
unclear.
Dysregulation of cyclin D1, 2, or 3: a possible early, unifying
event in MM. Despite the low proliferative index of MM tumors,
microarray expression analyses indicate that most tumors express
one of the cyclin D genes at a level that is similar to proliferating
PB, and distinctly higher than quiescent PC. The four recurrent
primary translocations appear to lead directly (11q13 - cyclin D1
or 6p21 - cyclin D3), or indirectly (4p16 and 16q23 - cyclin D2)
to cyclin D dysregulation. Another 20% of MM tumors express
cyclin D2, the major cyclin D gene expressed by normal PB.
Remarkably, however, despite the lack of expression of cyclin D1
in normal hematopoietic cells, about one third of MM tumors
express substantial levels of cyclin D1 in the absence of a
t(11;14) translocation; the mechanism responsible for cyclin D1
expression is obscure, but it is notable that this group of tumors
(that we call D1 lo) is represented rarely, if ever, by HMCL.
Perhaps, cyclin D1 expression requires a continued interaction of
the MM tumor cell and BM stromal cells.
Other oncogenic events in MM. Numeric (and possibly
structural) karyotypic abnormalities, including monosomy of
chromosome 13 or deletion of 13q14, are often present in MGUS,
but the timing and molecular consequences of these abnormalities
is unclear. Activating mutations of K- or N-RAS [or FGFR3 in
tumors with t(4;14)] are absent or rare in MGUS, but present in
40% of early MM, and perhaps 50% of advanced MM; this may
represent a marker if not a cause of progression from MGUS to
MM. Dysregulation of c-MYC, and mutations or mono-allelic
deletion of p53 appear to occur as very late progression events.
Presumably telomerase or the ALT pathway is activated during
tumorigeneis, but it is uncertain how or when this occurs.
Disruption of the Rb pathway occurs in most human tumors; but
even though dysregulation of cyclin D appears to be a universal
early event in MM, inactivation of RB or INK4 cyclin dependent
kinase inhibitors (p16INK4a and p18INK4c) can occur during
tumor progression and further disrupt the RB pathway.
P1.3
THE MYELOMA HIERARCHY: HETEROGENEITY
WITHIN THE MYELOMA CLONE
Linda M. Pilarski, Tony Reiman, Andrew R. Belch
Department of Oncology, University of Alberta and Cross Cancer
Institute
Early stage members of the multiple myeloma (MM) clone
contribute to disease progression: A variety of evidence suggests
that MM represents a hierarchy of monoclonal B lineage cells in
the blood and BM that includes late stage B cells and plasma
cells, pre-B-like cells and sIgM + pre-switch B cells. Others have
described circulating cells expressing the MM idiotype, and
circulating cells expressing the unique clonotypic IgH VDJ are
readily detectable in blood. We have shown that MM includes
circulating B cells that persist despite chemotherapy and may
mediate relapse. Even though MM plasma cells are often
severely depleted in response to therapy, residual disease and
bone lesions usually persist, suggesting a failure of therapy to
restore normal bone remodeling and the involvement of clinically
cryptic components of the MM clone. The heterogeneity seen
among ex-vivo clonotypic B and plasma cells suggests an in vivo
hierarchy of sequentially related differentiation stages. These
early stage members of the MM clone are morphologically
cryptic in that their physical appearance and phenotypic profiles
are largely normal, preventing their identification using as
“morphologically abnormal” cells. Only their expression of the
S16