Fiorenza Ianzini, PhD
Research Laboratory
Contact Information
Phone: 319-335-6544
1106/1108 Medical Laboratories
Molecular Regulators of Cell Cycle Progression and Mechanisms of Cancer Resistance to Treatment and Progression
Our interests focus on the effects of radiation exposure on cell cycle and on phenomena associated with cell cycle dysregulation. We have demonstrated that mitotic catastrophe (MC) occurs in a variety of mammalian cell lines exposed to a broad class of agents that induce a loss of regulation of cell division and it is characterized by the aberrant nuclear morphology observed following premature entry into mitosis and often results in the generation of aneuploid and polyploid cell progeny. Cells undergoing MC present an intact nuclear membrane, and they do not exhibit chromatin margination or extensive vacuolization as cells undergoing apoptosis do. In cells exposed to cytotoxic agents, activation of the pro-mitotic regulator cyclin B1/cdc2 kinase complex,
occurring while cells are delayed in S or G2 phases of the cell cycle, has been associated with the onset of nuclear fragmentation (MC), indicating that MC is the result of abrogation of cell cycle regulatory pathways, in particular the G2 checkpoint. Delayed de novo DNA damage also occurs at the time of MC induction. Although generally lethal, we and others have reported that a small fraction of cells which undergo radiation-induced MC can survive long enough to establish a growing population of cells. Using the Large Scale Digital Cell Analysis System (LSDCAS) we have also shown a high frequency of surviving clones containing an elevated incidence of MC in irradiated human-hamster hybrid GM10115 cells. Similarly, LSDCAS imaging of γ-irradiated HeLa cells has shown that a small fraction of MC cells are still alive 22 days post-irradiation and that some of these polyploid cells were able to successfully divide. These results indicate that a small fraction of cells can survive MC. In recent studies we have found that a small percentage of the polyploid cells formed via MC segregates nuclei, and
gives rise to viable descendants through cell divisions that present morphological features similar to those characteristic of meiotic prophase. The segregated cells contain only one nucleus and are morphologically indistinguishable from control cells. LSDCAS image data demonstrate that a fraction of the polyploid cells formed via radiation-induced MC escape death and gives rise to a progeny of smaller cells through a depolyploidization process. These results indicate that
a small fraction of cells with morphology identical to that of control cells originate from polyploid cells formed via radiation-induced MC; that is, polyploid tumor cells conserve their original individual genomic integrity and can re-initiate cell division via reduction division (meiosis). Work in our laboratory has been lately devoted at delving into the activation of these meiotic or pseudo-meiotic pathways
during depolyploidization of polyploid tumor cells formed via radiation-induced MC. Semi-quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR) and WB of irradiated tumor cells reveal mRNA and protein increases of a spectrum of meiotic genes involved in homologous recombination, sister chromatid cohesion, chromosome pairing and maintenance of the synaptonemal complex
structure. These data demonstrate that meiosis-specific genes are expressed in polyploid tumor cells formed via radiation-induced MC. This activation occurs in concert with the onset of a depolyploidization process as demonstrated by the LSDCAS imaging data. Thus, enabling the
hypothesis that a switch from a pro-mitotic to a pro-meiotic division regimen might be advantageous for the irradiated tumors to escape death.
The meiosis-specific genes found expressed in our studies can all be defined as cancer/testis antigens; and these findings suggest that
polyploid cells may have regulatory pathways in common with somatic reduction division and meiosis. These data also suggest that a conserved
mechanism of ordered genome assembly and disassembly exists in multi-genomic polyploid tumor cells, and that this process may take
advantage of the activation of pro-meiotic pathways to initiate depolyploidization. LSDCAS imaging data demonstrate that polyploid tumor
cells formed via radiation-induced MC are able to survive for many days post-irradiation and to undergo multipolar divisions
(depolyploidization). Some of these divisions are failed divisions and cell fusion occurs, some of these divisions start the process of
depolyploidization through reduction division giving rise to small mononucleated daughter cells indistinguishable from the untreated
control cells. If these newly formed mononucleated cells are in turn able to form viable colonies, they might be responsible for tumor
resistance to treatment and tumor progression. These cells will de facto have a disarrayed genomic composition; nevertheless, abnormal
chromosome arrangements may endow the tumor cells with properties that not only differentiate them from normal somatic cells, but may give to
the tumor cells growth advantages. Thus, these findings are relevant in understanding tumor progression and tumor resistance to treatment. We
are now characterizing the molecular mechanisms that allow depolyploidization of radiation-induced polyploid MC cells and the
potential for long term survival of the novel generated smaller mononucleated cell progeny. Understanding the specific mechanisms
underlying the temporary change from a pro-mitotic to a pro-meiotic division regimen will lend important insights into phenomena occurring
during human tumor progression and resistance.
Effects of High-LET Radiations in Normal Human Cells
In line with what discussed above, under the auspices of NASA (that has
funded a million dollar project – PI F. Ianzini) we are commencing
experiments aimed at identifying the role of high-LET radiation-induced
mitotic catastrophe in mutagenesis and its implication in
carcinogenesis. The rationale of these studies is based upon the notion
that during space flight astronauts are exposed to various types of
radiation and concerns have been raised regarding the genotoxic effects
of such exposure. In particular, radiation hazards in the space
environment include solar flares (or solar particle events, SPE),
geomagnetically trapped radiation, galactic cosmic radiation (GCR), and
secondary radiation. Solar storms periodically emit bursts of energetic
charged particles. These solar storms normally consist of protons (85
%), α-particles (5-10 %), and heavy charged ions (HZE) (5-10 %). A large
SPE could result in exposure to an HZE fluence of 3x107/cm2 and a proton flux of 1010 protons/cm2
with energies above 20 MeV. GCR consists of protons (85 %), α-particles
(14 %), and HZE particles (1-2 %) ranging in energy from 100 MeV to 10
GeV. At geosynchronous orbit, the GCR is essentially isotropic. HZE
particles (ions having a charge greater than 2 and an energy exceeding
50 MeV/nucleon) deposit energy as a function of the square of the charge
(Z) and the inverse of velocity. Consequently, even though they exist
in low abundance, GCR particles with Z greater than 3 are responsible
for an increased percentage of dose. As GCR enters the atmosphere, it
collides with atmospheric nuclei and breaks into pions and protons. The
pions subsequently decay into muons before striking the Earth. GCR
traversing the shielding of the spacecraft will also produce secondary
radiation consisting of HZE, pions, neutrons and protons. Secondary
radiation will also be produced when SPE protons and geomagnetically
trapped electrons and protons will interact with the spacecraft. Thus,
the resulting dose buildup from the bremsstrahlung radiation may be
significant. In fact, in tissue the buildup factor for protons of 500
MeV is greater than 3 at a depth of 20 cm. Moreover, due to the
unpredictability of SPE, it is possible that acute radiation exposures
in excess of 2 Gy may occur to the skin of occupants of orbiting space
satellites or during distant flights and explorations. Our studies will
be driven by our major hypothesis that iron and proton ions of varying
energies (providing high-LET values) induce mutations in exposed human
cells via processes occurring in cells that undergo mitotic
catastrophe. In particular, we will test the hypotheses that a) high-LET
radiation leads to an enhanced incidence of mitotic catastrophe; b) a
small proportion of irradiated cells undergoing mitotic catastrophe
escapes death and form viable colonies and c) mutations and altered
nucleosomal organization of chromatin (DNA damage) are persistent in
survivors of mitotic catastrophe cells thus making these cells prone to
cell transformation.