Characterization of Tcl1-Tg:P53-/- Mice That Resemble Human Chronic Lymphocytic Leukemia With 17P-Deletion

<p>Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the United Statesand Europe. CLL patients with deletion of chromosome 17p, where the tumor suppressor p53 gene is located, often develop a more aggressive disease with poor clinical outcomes. However, the underlying mechanism remains unclear. In order to understand the underneath mechanism <em>in vivo</em>, I have recently generated mice with E_u-<em>TCL1</em>-Tg:<em>p53</em>^-/- genotype and showed that these mice develop aggressive leukemia that resembles human CLL with 17p deletion. The E<em>_u</em>-<em>TCL1</em>-Tg:<em>p53</em>^-/-mice developed CLL disease at 3-4 months, significantly earlier than the parental E<em>_u</em>-<em>TCL1</em>-Tg mice that developed CLL disease at 8-12 months. Flow cytometry analysis showed that the CD5⁺/ IgM⁺ cell population appeared in the peritoneal cavity, bone marrow, and the spleens of E<em>_u</em>-<em>TCL1-Tg</em>:<em>p53</em>^-/-mice significantly earlier than that of the parental E<em>_u</em>-<em>TCL1</em>-Tg mice. Massive infiltration and accumulation of leukemia cells were found in the spleen and peritoneal cavity. <em>In vitro</em> study showed that the leukemia cells isolated from the E<em>_u</em>-<em>TCL1</em>-Tg:<em>p53</em>^-/-mice were more resistant to fludarabine treatment than the leukemia cells isolated from spleens of E<em>_u</em>-<em>TCL1</em>-Tg mice. Interestingly, TUNEL assay revealed that there was higher apoptotic cell death found in the E<em>_u</em>-<em>TCL1</em>-Tg spleen tissue compared to the spleens of the E<em>_u</em>-<em>TCL1-Tg</em>:<em>p53</em>^-/-mice, suggesting that the loss of p53 compromises the apoptotic process <em>in vivo</em>, and this might in part explain the drug resistant phenotype of CLL cells with 17p-deletion. In the present study, we further demonstrated that the p53 deficiency in the <em>TCL1</em> transgenic mice resulted in significant down-regulation of microRNAs miR-15a and miR16-1, associated with a substantial up-regulation of Mcl-1, suggesting that the p53-miR15a/16-Mcl-1 axis may play an important role in CLL pathogenesis. Interestingly, we also found that loss of p53 resulted in a significant decrease in expression of the miR-30 family especially miR-30d in leukemia lymphocytes from the E_u-<em>TCL1</em>-Tg:<em>p53</em>^-/- mice. Such down-regulation of those microRNAs and up-regulation of Mcl-1 were also found in primary leukemia cells from CLL patients with 17p deletion. To further exam the biological significance of decrease in the miR-30 family in CLL, we investigated the potential involvement of EZH2 (enhancer of zeste homolog 2), a component of the Polycomb repressive complex known to be a downstream target of miR-30d and plays a role in disease progression in several solid cancers. RT-PCR and western blot analyses showed that both EZH2 mRNA transcript and protein levels were significantly increased in the lymphocytes of E_u-<em>TCL1</em>-Tg:<em>p53</em>^-/- mice relative to E_u-<em>TCL1</em>-Tg mice. Exposure of leukemia cells isolated from E_u-<em>TCL1</em>-Tg:<em>p53</em>^-/- mice to the EZH2 inhibitor 3-deazaneplanocin (DZNep) led to induction of apoptosis, suggesting EZH2 may play a role in promoting CLL cell survival and this may contribute to the aggressive phenotype of CLL with loss of p53. Our study has created a novel CLL mouse model, and suggests that the p53/miR15a/16-Mcl-1 axis & p53/miR30d-EZH2 may contribute to the aggressive phenotype and drug resistance in CLL cells with loss of <em>p53</em>.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2013

Author dc:creator

• Liu, Jinyun

Contributors dc:contributor

• Peng Huang
• Paul J. Chiao
• Michael J. Keating

• Leukemia; p53; TCL1; mouse model; Drug resistance
• Laboratory and Basic Science Research

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/331

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-1366