Extracellular Superoxide Dismutase Regulates the Expression of GTPase Guanine Nucleotide Exchange Factors (GEFs), GTPase-activating proteins (GAPs), and Rho Guanine nucleotide disassociation inhibitors (GDI)

Extracellular superoxide dismutase (SOD3), which dismutases hydrogen peroxide to superoxide anion at cell membranes, mimics RAS oncogene action inducing primary cell immortalization at sustained low-level expression while high expression activates cancer barrier signaling through p53-p21 growth arrest pathway. We have previously demonstrated that the growth regulation of SOD3 occurs at the level of RAS and is mediated through non-transcriptional and transcriptional routes. Therefore, in the current work we assayed the growth suppressive mechanisms of SOD3 by characterizing the main signal transduction routes from the cell membrane into the nucleus. Based on our data robust over-expression of SOD3 in anaplastic thyroid cancer 8505c cells increased EGFR, RYK, ALK, FLT3, and EPHA10 tyrosine kinase receptor phosphorylation with consequent downstream SRC, FYN, YES, HCK, and LYN kinase activation. However, RAS pull-down experiment suggested lack of mitogen pathway stimulation that was confirmed by MEK1/2 and ERK1/2 Western blot. Interestingly, mRNA expression analysis indicated that SOD3 regulated in a dose dependent manner the expression of selected guanine nucleotide exchange factors (Rho GEF16, Ral GEF RGL1), GTPase activating proteins (ArfGAP ADAP2, Ras GAP RASAL1, RGS4), and Rho guanine nucleotide disassociation inhibitors (Rho GDI 2) therefore controlling the signal transduction through RAS GTPases to downstream signal transduction pathways. Our current data suggests a SOD3-induced activation of growth signal transduction is controlled in a dose dependent manner through GEF, GAP, and GDI.

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