Description:
<jats:title>Abstract</jats:title>
<jats:p>The surface glycoprotein CD20 is expressed on healthy and malignant B-cells and can be therapeutically exploited by monoclonal antibodies (e.g. Rituximab, Ofatumumab, GA-101). Stem cells and pro-B-cells are lacking CD20 surface protein, which allows the reestablishment of B-cell populations after treatment. Other cell lineages do not express CD20. Rituximab has revolutionized clinical practice in the treatment of malignant B-cell lymphoma. However, refractory lymphoma cells can lose the expression of CD20 after Rituximab exposure and B-cell lymphoma with low CD20 surface expression may be less responsive to treatment. Despite the widespread use of CD20 antibodies across lymphoma subtypes, little is known about the endogenous regulation of CD20. It was shown that several chemical compounds may modulate the surface density of CD20 (e.g. histone deacetylase inhibitors), but the regulatory network controlling CD20 levels is not understood. We aim to dissect the CD20 regulatome and to exploit the findings for novel therapeutic strategies.</jats:p>
<jats:p>The CD20 regulatome is studied in a Burkitt lymphoma cell line (Raji) characterized by medium expression of CD20 in comparison to other lymphoma models. As a proof of principle, we were able to down-regulate the surface expression of CD20 assayed by FACS with four independent silencing triggers targeting CD20 mRNA. To discover novel regulators of CD20 expression, we performed an unbiased genome-wide RNAi screen. The screen hits are involved in diverse molecular mechanisms such as signaling, trafficking, chromatin remodeling and membrane composition.</jats:p>
<jats:p>The group of genes decreasing the expression of CD20 expression can provide an insight into the physiological and pathological machinery involved in CD20 trafficking and processing. The strongest hit in this group, next to CD20 knockdown, is potentially involved in the direct transport of CD20 to the cell surface. Clinically most relevant is the group of genes where silencing increases the expression of CD20. The two strongest hits in this category are a transcription factor and a gene involved in signaling. Detailed molecular characterization of several chosen hits is currently ongoing. Their inhibition may lead to increased sensitivity to anti-CD20 antibodies and thus provide starting points for rational drug design.</jats:p>
<jats:p>Citation Format: Mikolaj Slabicki, Leopold Sellner, Alexander Jethwa, Michael Boettcher, Thorsten Zenz. Modulating therapeutic targets in B-cell lymphoma: Loss-of-function RNAi screen for CD20 regulators. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3159. doi:10.1158/1538-7445.AM2013-3159</jats:p>