Autologous Bone Marrow Transplantation - Blog Science Connections

724 Aberrant Gene Expression in AML
ciated with particular leukemias; this may lead to deregulated expression of
these oncogenes. Furthermore, structural abnormalities and amplifications
associated with the enhanced expression of cellular oncogenes have been
consistently observed in neoplastic hematopoietic cells.
At the moment, no monitor system exists for the presence of leukemic
cells in remission. The leukemic colony-forming-cell (CFC-Le) assays are not
suitable for detecting leukemic cells in remission, since the culture conditions
used also give rise to colonies derived from normal cells. In addition, the
frequency of CFC-Le is low, 0.01% to 0.1% of the leukemic-cell population,
which makes detection in remission unlikely. Because of these limitations,
we have begun to investigate the use of molecular hybridization technologies,
in particular RNA in situ hybridization, as sensitive detection methods for
leukemic cells.
Expression
Levels
RESULTS AMD DISCUSSION
Northern Blot Analyses
We have found that many of the proto-oncogenes studied were expressed
in human normal bone marrow (Table 1). These data support the idea that
these genes play a role in adult normal hematopoietic metabolism. Most of
these genes (with the exception of c-fos) are expressed at very low levels in
normal marrow samples. In contrast to the constant low-level expression of
these genes in normal cells, their level of expression is high, but variable, in
different forms of leukemia (Table 1). This high level of expression is
particularly noticeable for c-myc in all leukemic samples studied. Cinder
conditions where c-myc expression is barely detectable in normal bone
marrow samples after northern blot hybridization to a 32 P-labeled probe, a
strong signal is obtained for all acute leukemia samples tested. Although this
increase in signal may simply be a result of an increase in the proportion of
proliferating blast cells present in the cell population, it may also reflect an
overexpression of c-myc in the leukemic cell population.
Transcript Size
There are data to suggest that the presence of an aberrantly sized
transcript of certain proto-oncogenes is associated with leukemia (10). In all
but two cases, c-fes and c-K-ras, the transcript size present in normal
hematopoietic cells is the same as that detected in leukemia (Table 1). When
probing with c-fes, we find a broad hybridization band probably representing
two or three unresolved bands. In some, samples the transcript size is slightly
smaller than 2.7 kb and in other samples slightly larger. We can find no
correlation between the varying transcript sizes and the samples tested. This
leads us to believe that the ability to detect an aberrant transcript will be