Browsing by Author "Abu-Sultanah, Mohannad"

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    Genetic disruption of the small GTPase RAC1 prevents plexiform neurofibroma formation in mice with neurofibromatosis type 1
    (Elsevier, 2020-07-17) Mund, Julie A.; Park, SuJung; Smith, Abbi E.; He, Yongzheng; Jiang, Li; Hawley, Eric; Roberson, Michelle J.; Mitchell, Dana K.; Abu-Sultanah, Mohannad; Yuan, Jin; Bessler, Waylan K.; Sandusky, George; Chen, Shi; Zhang, Chi; Rhodes, Steven D.; Clapp, D. Wade; Pediatrics, School of Medicine
    Neurofibromatosis type 1 (NF1) is a common cancer predisposition syndrome caused by mutations in the NF1 tumor suppressor gene. NF1 encodes neurofibromin, a GTPase-activating protein for RAS proto-oncogene GTPase (RAS). Plexiform neurofibromas are a hallmark of NF1 and result from loss of heterozygosity of NF1 in Schwann cells, leading to constitutively activated p21RAS. Given the inability to target p21RAS directly, here we performed an shRNA library screen of all human kinases and Rho-GTPases in a patient-derived NF1-/- Schwann cell line to identify novel therapeutic targets to disrupt PN formation and progression. Rho family members, including Rac family small GTPase 1 (RAC1), were identified as candidates. Corroborating these findings, we observed that shRNA-mediated knockdown of RAC1 reduces cell proliferation and phosphorylation of extracellular signal-regulated kinase (ERK) in NF1-/- Schwann cells. Genetically engineered Nf1flox/flox;PostnCre+ mice, which develop multiple PNs, also exhibited increased RAC1-GTP and phospho-ERK levels compared with Nf1flox/flox;PostnCre- littermates. Notably, mice in which both Nf1 and Rac1 loci were disrupted (Nf1flox/floxRac1flox/flox;PostnCre+) were completely free of tumors and had normal phospho-ERK activity compared with Nf1flox/flox ;PostnCre+ mice. We conclude that the RAC1-GTPase is a key downstream node of RAS and that genetic disruption of the Rac1 allele completely prevents PN tumor formation in vivo in mice.
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    TGFβ-dependent signaling drives tumor growth and aberrant extracellular matrix dynamics in NF1-associated plexiform neurofibroma
    (American Association for the Advancement of Science, 2025) Abu-Sultanah, Mohannad; Zhou, Zhuan; Jiang, Chunhui; Mitchell, Dana K.; Bessler, Waylan K.; Jiang, Li; Li, Xiaohong; Qian, Shaomin; Smith, Abbi E.; Mang, Henry E.; White, Emily E.; Ciesielski, Marisa D.; Hickey, Brooke E.; Brewster, Kylee M.; Sandusky, George E.; Masters, Andi; Angus, Steven P.; Clapp, D. Wade; Le, Lu Q.; Rhodes, Steven D.; Pediatrics, School of Medicine
    Plexiform neurofibromas (PNFs) are benign tumors of the peripheral nervous system that represent a major source of morbidity in neurofibromatosis type 1 (NF1). A substantial proportion of patients do not respond to current therapies or experience intolerable side effects. Transcriptomic characterization of murine and human PNF at bulk and single-cell resolution identified transforming growth factor-β (TGFβ) signaling as a key upstream regulator, driving aberrant basement membrane (BM) protein production by neoplastic Schwann cells and Fbs. Conditional TGFβ1 overexpression in Nf1-deficient Schwann cells driven by Hoxb7-Cre promoted PNF growth and malignant transformation in vivo. Conversely, pharmacologic inhibition of the type I TGFβ receptor (TGFβRI) reduced PNF tumor burden in Nf1 mutant mice. Proteomic characterization of the extracellular matrix (ECM) showed reduced BM proteins upon TGFβRI inhibition. These findings implicate TGFβ as a potential therapeutic target in PNF and provide insights into the role of TGFβ signaling in orchestrating ECM dynamics in the PNF microenvironment.