Abstract 2325: The mechanistic basis of BMP2 activation in NF1-deficient malignant peripheral nerve sheath tumors

Neurofibromatosis type I (NF1)-deficient malignant peripheral nerve sheath tumor (MPNST) is an aggressive tumor for which the only treatment option is surgical removal with wide margins, often leaving behind cancer cells needing chemotherapy. Ras-GAP related domain (GRD) is the most widely studied functional target of Nf1 implicated in tumorigenesis, however, therapeutic interventions targeting Ras activity have met with limited success. Using gene expression profiling, we identified bone morphogenetic protein 2 (BMP2) signaling pathways as a therapeutic target in MPNSTs, independent of the NRAS and MEK1/2 regulation. This novel finding addresses an understudied aspect of the signaling cascades downstream of neurofibromin deficiency, independent of the RAS-GRD domain. Consistent with our data, gene expression studies from NF1 patient tissue samples demonstrated that increased expression of BMP2 was associated with malignancy in NF1 patients [Miller SJ et al., EMBO Mol Med. 1:236-48. 2009]. Furthermore, we have shown that inhibition of the BMP2 receptor by LDN-193189 decreases invasiveness and cellular migration in MPNST cell lines [Sun D et al., MCR, 11: 616-27, 2013]. The mechanism by which NF1-deficiency leads to hyperactivation of BMP2 signaling pathways, and consequently increased cellular motility and invasion is unknown. Using NF1-wt and NF1-kd sporadic MPNST cell lines, we are investigating the transcriptional regulation of BMP2 upon NF1 deficiency to identify signaling mechanisms downstream of NF1 mediating increase in BMP2 levels. The goal of this work is to determine whether NF1 knockdown regulates BMP2 transcription through initiation and rate of transcription or post-transcriptionally. This will be assessed using promoter-reporter assays and mRNA half-life studies. We will present BMP2 reporter activity analysis using various constructs of the BMP2 promoter, and show BMP2 transcript stability upon NF1 kd. Using these data, we will identify and functionally validate signaling pathways mediating BMP2 activation as the readout using small molecular inhibitors. Clinical trials have demonstrated the limited efficacy of inhibition of the RAS-MEK, and PI3K-AKT-mTOR axis in NF1 patients. The BMP2, Smad pathway is involved in cellular motility and invasiveness, characteristic of the aggressive MPNSTs. Therefore, we will present a combinatorial approach that targets the growth and proliferative potential of MPNSTs by RAS-MEK and PI3K inhibitors, along wi