THE ROLE OF THE MIR-17-92 CLUSTER IN HDI-RESISTANT DLBCL CELL LINES

William Pinkston , Catharine L. Smith, Ph.D.

THE ROLE OF THE MIR-17-92 CLUSTER IN HDI-RESISTANT DLBCL CELL LINES

Diffuse large B-cell lymphoma (DLBCL) is the most aggressive form of non-Hodgkin’s lymphoma (NHL), with 30-40 percent of cases considered fatal even after treatment. DLBCL drug-resistance can be partially attributed to the heterogeneity of the disease but a complete mechanism of action is not understood. Considering this, the search for new therapeutic regimens that increase the survival rates of patients is of interest in our research efforts. Histone deacetylase inhibitors (HDI) are a promising class of drugs, which induce apoptosis in certain DLBCL cell lines. Sensitivity to the drug is marked by a G2/M phase arrest and subsequent apoptosis after 24 hours of treatment. Resistant cells undergo G1 arrest but do not undergo apoptosis and continue proliferating after the drug is removed. Expression profiling analysis in various DLBCL lines following PXD101-treatment (a hydroxamate HDI) showed that levels of a particular c-Myc regulated polycistronic micro RNA (miRNA) cluster known as miR-17-92 were significantly lower in sensitive cell lines but not in resistant lines. Various studies have confirmed that the miR-17-92 cluster is indeed oncogenic with targets involved in cell cycle progression (i.e. p21Cip1/Waf1) and apoptosis (i.e. E2F1). Given these findings, we are concerned with any role this cluster might play in resistance to PXD101 treatment. Real-time qPCR data gathered in our lab from 3 replicate experiments in 5 DLBCL cell lines shows the primary transcript (pri-miR-17) is down-regulated in both sensitive and resistant lines within 8 hours of treatment with PXD101. However, Ji et al. (2008) showed that primary RNA levels do not correlate to levels of the individual miRNA, suggesting differential regulation of the pri-miR-17 transcript. Therefore, to address the cluster’s role in resistance to HDI-treatment, we will need to determine the levels of the individual miRNA and their suspected targets in response to PXD101 treatment, combining an LNA-based RT-qPCR method to detect short sequence miRNA and a SYBR Green RT-qPCR method to measure suspected target-mRNA transcripts. Funding for this project is made possible through grant number 1 P50 CA-130805-05.

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