tumor cell biology program - Sylvester Comprehensive Cancer Center

elucidate complete RNA maturation
pathways and to study the regulation of
these processes.
The second area of investigation
deals with the translation system of mammalian
cells. Protein synthesis in mammalian
cells proceeds as much as 100-fold
faster than synthesis is isolated cell-free
systems. What is lost in these in vitro
systems is the organization that normally
exists in vivo. They have shown that
many of the components of the translation
apparatus are associated with each
other, and that protein synthesis is a
“channeled” pathway, i.e., the aminoacyltRNA
and peptidyl-tRNA intermediates
are directly transferred from one component
of the translation apparatus to the
next without dissociation into the cellular
fluid. A permeabilized mammalian
cell system has been developed that allows
study of these events in close to an
in vivo situation. Studies are in progress
to determine the role of the actin cytoskeleton
in maintaining the organization
of the translation system and to identify
other factors associated with the translation
apparatus that affect its function.
PUBLICATIONS
Li, Z, Pandit, S and Deutscher, MP.
Maturation of 23S ribosomal RNA requires
the exoribonuclease RNase T.
RNA 5:139, 1999.
Ghosh, S and Deutscher, MP. Oligoribonuclease
is an essential component
of the messenger RNA decay pathway.
Proceedings National Academy of Science
USA 96:4372, 1999.
Li, Z, Pandit, S and Deutscher, MP.
RNase G (CafA Protein) and RNase E
are both required for the 5’ maturation
of 16S ribosomal RNA. Embolism Journal
18:2878, 1999.
Zuo, Y and Deutscher, MP. The
DNase activity of RNase T and its application
to DNA cloning. Nucleic Acid
Research 27:4077, 1999.
Callahan, C, Neri-Cortes, D and
Deutscher, MP. Purification and characterization
of the tRNA-processing enzyme
RNase BN. Journal of Biological
Chemistry 275:1030, 1999.
Nathanson, L and Deutscher, MP.
Accelerated publication - Active aminoacyltRNA
synthetases are present in nuclei
as a high molecular weight multienzyme
complex. Journal of Biological Chemistry
275:31559, 2000.
Deutscher, MP and Li, ZW. Exoribonucleases
and their multiple roles in
RNA metabolism. Progress in Nucleic
Acid Research and Molecular Biology
66:67, 2001.
Zuo, YH and Deutscher, MP.
Exoribonuclease superfamilies: structural
analysis and phylogenetic distribution.
Nucleic Acids Research 29:1017, 2001.
HIGHLIGHTS/DISCOVERIES
• Dr. Deutscher’s team discovered a new
endoribonuclease, which has been
called RNase G. This enzyme was
shown to be essential for the maturation
of the 5’ terminus of E. coli 16S
ribosomal RNA as part of a two-step
process that also requires a second
endoribonuclease, RNase E. This team
has also identified RNase T as the enzyme
that matures the 3’ terminus of
23S ribosomal RNA. Degradation of
messenger RNA also was studied. They
found that the enzyme oligoribonuclease
is an essential component of this
process and that in its absence small
oligoribonucleotides derived from
mRNA, accumulate.
• Dr. Deutscher’s laboratory has developed
an efficient, cell-free translation
system that synthesizes protein at about
30 percent of the in vivo rate. This
compares with the one to two percent
generally obtained in other systems.
Development of this system depended
on stabilization of the actin cytoskeleton
during cell disruption. In a second
study they have found that
aminoacyl-tRNA synthetases are
present in an active form in mammalian
cell nuclei, and that these enzymes
exist as part of a multi-enzyme complex,
that is analogous to, but more
stable than the cytoplasmic complex.
Nevis Fregien, Ph.D.
Associate Professor of
Cell Biology and Anatomy
DESCRIPTION OF RESEARCH
The research being conducted in Dr.
Fregien’s laboratory focuses on understanding
the molecular basis for the
progression of noninvasive tumor cells
into highly aggressive, metastatic cancer
cells. This is an extremely important
problem for developing anticancer therapies,
because this metastatic ability to
migrate throughout the body and generate
multiple tumors is the most life
threatening aspect of cancer. Since they
believe that the cellular properties associated
with metastasis involve molecules
expressed on the cell surface, their approach
is to identify changes in the cell
surface molecules expressed by metastatic
cells and determine how they are regulated
and how they might affect metastatic
cellular properties. One specific
change in molecules expressed by metastatic
cells is an increase in the amount
and complexity of oligosaccharide structures
post-translationally added to cell
surface proteins. The synthesis of these
oligosaccharides is accomplished by a
number of enzymes known as glycosyltransferases.
Dr. Fregien’s laboratory
has shown that one of the glycosyltransferases,
N-acetylglucosa-minyltransferase
V, is over-expressed in tumor
cells. Furthermore, this elevated expression
is due to activation of the promoter
for this gene by the action of some
oncogenes such as src and neu. This
shows that oncogenes do not only stimulate
uncontrolled cellular proliferation,
as previously believed, but they also cause
changes, which can affect the cell surface.
Dr. Fregien’s group is trying to understand
the regulation of this promoter
as well as the promoter of a similar gene,
the Core 2 transferase, with the hope that
this information will be useful to design
therapies to turn off the expression of
these genes and inhibit metastatic
progession.
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UM/Sylvester Comprehensive Cancer Center Scientific Report 2002