MR-01 * MicroRNA-145 REGULATES JAM-A EXPRESSION AND COMPROMISES GLIOBLASTOMA MAINTENANCE

Abstract

Glioblastoma is composed of heterogeneous cellular populations, including self-renewing, tumorigenic cancer stem cells (CSCs). Discrete anatomical niches have been described where CSCs communicate with their surroundings to promote their self-renewal, tumor maintenance and increased resistance to conventional therapies. Therefore, signaling molecules involved in cell-cell interactions and the associated regulatory mechanisms are vital to CSC function. CSC interaction with their niche via adhesion proteins is critical for CSC maintenance, and enhanced adhesion is a hallmark of stemness. In the context of cancer, gene expression is regulated through the upregulation or downregulation of specific microRNAs (miRNAs). The interaction between miRNAs and proteins involved in niche adhesion and communication remains largely unexplored. Junctional adhesion molecule A (JAM-A) is a CSC-specific adhesion protein and its targeting decreases self-renewal and tumorigenicity. To determine whether JAM-A promotes self-renewal, we overexpressed JAM-A and observed an increase in proliferation, self-renewal, and tumor formation. In order to link this adhesion mechanism to a larger signaling network, we evaluated the upstream mechanisms by which JAM-A is regulated and specifically expressed by CSCs. By analyzing miRNAs, we found that JAM-A expression is suppressed by miR-145 and confirmed JAM-A as a direct target of mir-145 using luciferase constructs. miR-145 has previously been described to be a negative regulator of glioblastoma growth, and we found that non-CSCs expressed high levels of miR-145 while CSCs expressed low miR-145, correlating to differences in JAM-A expression between CSCs and non-CSCs. Introduction of miR-145 into CSCs decreased self-renewal, stem cell marker expression (SOX2, OCT4 and NANOG) and activation of self-renewal pathways (STAT3 and AKT). Mechanistic studies are in progress to determine how miR-145 and JAM-A interact to control stem cell and self-renewal pathways. Our results link CSC-specific adhesion to a microRNA regulatory network that is altered in glioblastoma.