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Abstract 1363 The role of HDACs in cell biology, initially limited to their effects upon histones, encompasses now more complex regulatory functions that are dependent on their tissue expression, cellular compartment distribution and the stage of cellular differentiation. Not surprisingly, HDACs have been shown to play important roles in normal B-cell biology and, aberrant expression of these proteins has been found in some B-cell malignancies1. However, the role of specific HDACs in regulation of pro-survival and cell-cycling genes in MCL and CLL still remains poorly understood. We therefore evaluated by RT-PCR the mRNA expression of specific HDACs in MCL and CLL cell lines and in primary cells from patients with these B-cell malignancies. Our analysis revealed a unique and opposing expression of HDAC10 and HDAC11 in these malignant B-cells. While HDAC11 over-expression was frequently found in MCL and CLL cells, in particular in patients with aggressive disease, an almost complete abrogation of HDAC10 was observed in malignant B-cells as compared to normal B-cell controls. These findings led us to explore the biological consequences of manipulating HDAC11 and HDAC10 in MCL and CLL cells. First, knocking-down HDAC11 (HDAC11KD) using lentiviral shRNA resulted in downregulation of cyclin D1, Cdkn1a (p21) and bcl-2. Furthermore, HDAC11KD MCL or CLL cells displayed a slower cell proliferation relative to non-target shRNA control cells. Cell cycle analysis revealed that HDAC11KD clones are arrested in G1. Conversely, over-expression of HDAC11 in the MCL cell line Z138c or in the CLL cell line MEC1 resulted in enhanced cell survival and increased proliferative capacity. Mechanistically, we have recently found that HDAC11 over-expression is associated with increased phosphorylation of STAT3, a known survival pathway in malignant B-cells. Second, HDAC10 belongs to the class II HDAC family and its biological functions remain largely unknown. Similar to our results in aggressive MCL and CLL, a decreased HDAC10 expression has been reported in patients with aggressive solid tumors2, suggesting that loss of HDAC10 expression might confer a survival advantage to malignant cells. Indeed, over-expression of HDAC10 in Z138c and MEC1 cells resulted in a rapid induction of cell death in vitro with only 5% of cells being alive at 48 hours. Our results highlight the need for a better understanding of the expression/function of specific HDACs in MCL and CLL biology. The findings of opposing roles for HDAC11 and HDAC10 in influencing cell survival and proliferation might explain the limited efficacy of pan-HDAC inhibitors (with their indiscriminate inhibition of multiple HDACs) in these B-cell malignancies, and provide support for the development of isotype-selective inhibitors targeting HDAC11. Disclosures: Chen-Kiang: Pfizer, Inc.: Research Funding. |
