Page 265 - 2014 Printable Abstract Book
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in the BM after particle IR in C57BL/6 mice were determined at 1, 2, 4, 8, 12, 28 and 40 weeks post-IR.
BM-derived mononuclear cells were triple-stained with RAM34 (CD34, c-kit, and Sca1), AC133, and
hematopoietic lineage negative cocktail, then sorted by FASC for E- and L-MPP. BM EPCs ex-vivo - There
was a transient 2.5-3.5-fold increase in BM-EPC apoptosis, with 3.5-fold increases for 56Fe and 1H at 5hrs
and 24hrs, respectively that was no longer detected by day 7. Subsequently, there was a 3-fold increase
in BM-EPC apoptosis on day 28 for both ion-IR mice. Compared to 24 hrs, there was a ~20% (1H) and ~45%
(56Fe) increase in the rate of EPC proliferation on day 14 that returned to control levels on day 28. BM E-
MPP and L-MPP in vivo - Compared to control mice, 1H-IR increased the number of both E-MPPs (665%)
and L-MPPs (203%), whereas 56Fe-IR decreased E-MPP (74%) and L-MPPs (65%) at 1 week post-IR,
suggesting stimulation by 1H but overt damage by 56Fe in the BM milieu. In 56Fe-IR mice, E-MPPs
recovered between 4 and 12 weeks, followed by declines at later time points. In 1H-IR mice, E-MPPs were
near control levels up to 4 weeks, but declined at later time points. The long-lasting and cyclical effects of
IR on the BM E- and L-MPPs after a single 1H or 56Fe IR dose suggests the presence of prolonged and non-
targeted effects in BM milieu, that occur in cells that were not traversed by IR, rather induced by signals
from IR cells. Our studies showed that, both 1H- and 56Fe-IR has profound and long-lasting (28-40 months)
negative effects on the number of E- and L-MPPs. Future longitudinal studies are necessary to determine
whether BM progenitor cell populations may be affected after low dose terrestrial IR exposure, such as
full body CT and PET scans, as well as in astronauts after deep space missions.
(PS4-50) Non-canonical roles of telomerase promote ionizing radiation induced breast cancer stem cell
1
1
enrichment via conditional reprogramming. Brock J. Sishc, PhD ; Christopher Nelson ; Xuefeng Gao,
1
1
2
2
PhD ; Christine Battaglia ; Lynn Hlatky, PhD ; and Susan Bailey, PhD, Colorado State University, Fort
Collins, CO and Center of Cancer Systems Biology, Tufts University School of Medicine, Boston, MA
2
1
Differential expression of telomerase, the specialized reverse transcriptase recognized primarily
for maintaining telomere length, serves to limit the replicative lifespan of normal cells (low levels pro-
posed as a tumor suppressor), while its deregulation/reactivation enables carcinogenesis (high levels
proposed as an oncogene). Interestingly, a number of reports have demonstrated that ionizing radiation
(IR) elevates telomerase activity in a variety of cancer cell lines post exposure, suggesting potential roles
not only in promoting tumor repopulation following radiation therapy, but in tumor formation as well. As
IR exposure has also been shown to increase cancer stem cell (CSC) populations in breast cancer cell lines,
we hypothesized that telomerase may be a key regulator in this process. Indeed, inhibition of telomerase
activity effectively blocked IR-induced enrichment of CSC populations in both the MCF-7 breast carcinoma
and MCF-10A non-tumorigenic mammary epithelial cell lines. Cell-by-cell imaging revealed that despite
elevated telomerase activity post IR exposure, telomeres were significantly shortened in a very short time
frame. Our results suggest that telomerase is participating in IR-induced CSC enrichment apart from its
canonical role in telomere elongation, and support the view that telo-merase may underlie many, if not
all, of the hallmarks of cancer. On-going modeling efforts address whether telomerase acts to promote
IR-induced breast CSC enrichment through symmetric division of inherently radioresistant CSCs
(mobilization/proliferation), or through activation of pathways that pro-mote the reprogramming of non-
stem cells into CSCs (de-differentiation/non-proliferative) or both. Support for this research from NASA
(NNX08AB65G) is gratefully acknowledged.
263 | P a g e
BM-derived mononuclear cells were triple-stained with RAM34 (CD34, c-kit, and Sca1), AC133, and
hematopoietic lineage negative cocktail, then sorted by FASC for E- and L-MPP. BM EPCs ex-vivo - There
was a transient 2.5-3.5-fold increase in BM-EPC apoptosis, with 3.5-fold increases for 56Fe and 1H at 5hrs
and 24hrs, respectively that was no longer detected by day 7. Subsequently, there was a 3-fold increase
in BM-EPC apoptosis on day 28 for both ion-IR mice. Compared to 24 hrs, there was a ~20% (1H) and ~45%
(56Fe) increase in the rate of EPC proliferation on day 14 that returned to control levels on day 28. BM E-
MPP and L-MPP in vivo - Compared to control mice, 1H-IR increased the number of both E-MPPs (665%)
and L-MPPs (203%), whereas 56Fe-IR decreased E-MPP (74%) and L-MPPs (65%) at 1 week post-IR,
suggesting stimulation by 1H but overt damage by 56Fe in the BM milieu. In 56Fe-IR mice, E-MPPs
recovered between 4 and 12 weeks, followed by declines at later time points. In 1H-IR mice, E-MPPs were
near control levels up to 4 weeks, but declined at later time points. The long-lasting and cyclical effects of
IR on the BM E- and L-MPPs after a single 1H or 56Fe IR dose suggests the presence of prolonged and non-
targeted effects in BM milieu, that occur in cells that were not traversed by IR, rather induced by signals
from IR cells. Our studies showed that, both 1H- and 56Fe-IR has profound and long-lasting (28-40 months)
negative effects on the number of E- and L-MPPs. Future longitudinal studies are necessary to determine
whether BM progenitor cell populations may be affected after low dose terrestrial IR exposure, such as
full body CT and PET scans, as well as in astronauts after deep space missions.
(PS4-50) Non-canonical roles of telomerase promote ionizing radiation induced breast cancer stem cell
1
1
enrichment via conditional reprogramming. Brock J. Sishc, PhD ; Christopher Nelson ; Xuefeng Gao,
1
1
2
2
PhD ; Christine Battaglia ; Lynn Hlatky, PhD ; and Susan Bailey, PhD, Colorado State University, Fort
Collins, CO and Center of Cancer Systems Biology, Tufts University School of Medicine, Boston, MA
2
1
Differential expression of telomerase, the specialized reverse transcriptase recognized primarily
for maintaining telomere length, serves to limit the replicative lifespan of normal cells (low levels pro-
posed as a tumor suppressor), while its deregulation/reactivation enables carcinogenesis (high levels
proposed as an oncogene). Interestingly, a number of reports have demonstrated that ionizing radiation
(IR) elevates telomerase activity in a variety of cancer cell lines post exposure, suggesting potential roles
not only in promoting tumor repopulation following radiation therapy, but in tumor formation as well. As
IR exposure has also been shown to increase cancer stem cell (CSC) populations in breast cancer cell lines,
we hypothesized that telomerase may be a key regulator in this process. Indeed, inhibition of telomerase
activity effectively blocked IR-induced enrichment of CSC populations in both the MCF-7 breast carcinoma
and MCF-10A non-tumorigenic mammary epithelial cell lines. Cell-by-cell imaging revealed that despite
elevated telomerase activity post IR exposure, telomeres were significantly shortened in a very short time
frame. Our results suggest that telomerase is participating in IR-induced CSC enrichment apart from its
canonical role in telomere elongation, and support the view that telo-merase may underlie many, if not
all, of the hallmarks of cancer. On-going modeling efforts address whether telomerase acts to promote
IR-induced breast CSC enrichment through symmetric division of inherently radioresistant CSCs
(mobilization/proliferation), or through activation of pathways that pro-mote the reprogramming of non-
stem cells into CSCs (de-differentiation/non-proliferative) or both. Support for this research from NASA
(NNX08AB65G) is gratefully acknowledged.
263 | P a g e
