C-MYB CONTROLS THE LEVEL OF GLUCOCORTICOID RECEPTOR IN ACUTE L YMPHOBLASTIC LEUKEMIA CELLS AND AFFECTS THE SENSITIVITY OF L YMPHOBLASTS TO STEROID HORMONE THERAPY
Document Type
Presentation
Start Date
22-10-2010 10:00 AM
End Date
22-10-2010 10:15 AM
Description
Glucocorticoid (GC) steroid hormones are a mainstay in combination therapy for patients diagnosed with acute lymphoblastic leukemia (ALL). They are valuable because of their proapoptotic effects in ALL blasts. The cellular function of GCs is mediated by the glucocorticoid receptor (GR) protein. In pre-B-cell (697) and T-cell (CEM-C7) ALL cell lines, GC treatment results in an auto-upregulation of GR mRNA transcripts and protein. This increase in GR correlates with an apoptotic response in both cell lines (GC-sensitivity). We have discovered a novel glucocorticoid response unit (GRU) that is present in at least three promoters for the GR gene. When the GC binds to the GR protein, the GR interacts at the GRU in concert with the cMyb transcription factor to auto-upregulate the GR mRNA and protein levels in the cell. The specific aim of this study was to test the hypothesis that the c-Myb transcription factor directly interacts with the GR at the GRU, regulates the levels of GR transcripts and protein in the cells, and that this affects the sensitivity of the cell to the steroid hormone. To test this hypothesis, a new cell line, 697-sh-c-Myb-E10, has been established, wherein the knockdown of c-Myb is controllable by doxycycline (Doxy). Western blotting of lysates from the Doxy pre-treated samples showed a gradual decrease in c-Myb protein levels with increasing Doxy concentrations. Interestingly, a gradual decrease in GR protein level was also observed with increasing Doxy concentrations, suggesting that the c-Myb transcription factor controls the level of GR protein in these cells. Also, by GST fusion protein pull-down assay, we showed that c-Myb directly interacts with GR, suggesting that the knockdown of c-Myb affects the level of GR in these cells because the formation of a GR, c-Myb, GRU ternary complex is reduced. However, instead of reducing the sensitivity of the cell to steroid, the knockdown of c-Myb, by itself, reduced the viability of pre-BALL 697 cells, led to a cell cycle arrest, and sensitized the cells to GC treatment. Thus, novel therapeutic approaches aimed at both decreasing the intracellular levels of c-Myb and increasing the intracellular levels of GR may be particularly powerful in the treatment of GC-resistant ALL.
Recommended Citation
Sarvaiya, Purvaba J.; Schwartz, Jason R.; and Vedeckis, Wayne V., "C-MYB CONTROLS THE LEVEL OF GLUCOCORTICOID RECEPTOR IN ACUTE L YMPHOBLASTIC LEUKEMIA CELLS AND AFFECTS THE SENSITIVITY OF L YMPHOBLASTS TO STEROID HORMONE THERAPY" (2010). Dr. Joseph M. Moerschbaecher, III Graduate Research Day. 7.
https://digitalscholar.lsuhsc.edu/grad_rs/2010/presentation1/7
C-MYB CONTROLS THE LEVEL OF GLUCOCORTICOID RECEPTOR IN ACUTE L YMPHOBLASTIC LEUKEMIA CELLS AND AFFECTS THE SENSITIVITY OF L YMPHOBLASTS TO STEROID HORMONE THERAPY
Glucocorticoid (GC) steroid hormones are a mainstay in combination therapy for patients diagnosed with acute lymphoblastic leukemia (ALL). They are valuable because of their proapoptotic effects in ALL blasts. The cellular function of GCs is mediated by the glucocorticoid receptor (GR) protein. In pre-B-cell (697) and T-cell (CEM-C7) ALL cell lines, GC treatment results in an auto-upregulation of GR mRNA transcripts and protein. This increase in GR correlates with an apoptotic response in both cell lines (GC-sensitivity). We have discovered a novel glucocorticoid response unit (GRU) that is present in at least three promoters for the GR gene. When the GC binds to the GR protein, the GR interacts at the GRU in concert with the cMyb transcription factor to auto-upregulate the GR mRNA and protein levels in the cell. The specific aim of this study was to test the hypothesis that the c-Myb transcription factor directly interacts with the GR at the GRU, regulates the levels of GR transcripts and protein in the cells, and that this affects the sensitivity of the cell to the steroid hormone. To test this hypothesis, a new cell line, 697-sh-c-Myb-E10, has been established, wherein the knockdown of c-Myb is controllable by doxycycline (Doxy). Western blotting of lysates from the Doxy pre-treated samples showed a gradual decrease in c-Myb protein levels with increasing Doxy concentrations. Interestingly, a gradual decrease in GR protein level was also observed with increasing Doxy concentrations, suggesting that the c-Myb transcription factor controls the level of GR protein in these cells. Also, by GST fusion protein pull-down assay, we showed that c-Myb directly interacts with GR, suggesting that the knockdown of c-Myb affects the level of GR in these cells because the formation of a GR, c-Myb, GRU ternary complex is reduced. However, instead of reducing the sensitivity of the cell to steroid, the knockdown of c-Myb, by itself, reduced the viability of pre-BALL 697 cells, led to a cell cycle arrest, and sensitized the cells to GC treatment. Thus, novel therapeutic approaches aimed at both decreasing the intracellular levels of c-Myb and increasing the intracellular levels of GR may be particularly powerful in the treatment of GC-resistant ALL.