Retracing RAS signaling by correlating protein expression in different subtypes of neurofibromatosis 1-associated nerve sheath tumors.

Aims: Expression patterns of key proteins involved in RAS signaling and connected pathways were determined and correlated to possibly provide information for therapeutic application of RAS inhibitors in neurofibromatosis type 1 (NF1)-associated peripheral nerve sheath tumors (PNST).

Materials and methods: Clinical variables (age, sex), histological parameters (cell density, mitoses), and expression of immunohistochemically evaluated ligand and receptor proteins (neuregulin 1 (NRG1), ErbB2, ErbB3), RAS pathway proteins (mTor, Rho, phosphorylated MEK), transcription factors (Pax7, Sox9), and proliferation marker Ki-67, were correlated in cutaneous (CNF, n = 136), diffuse (DNF, n = 123)/diffuse plexiform (DPNF, n = 113), and plexiform neurofibroma (PNF, n = 126), and in malignant PNST (MPNST, n = 22).

Results: In CNF, NRG1 correlated with Ki-67 and Pax7. Further, mTOR correlated with ErbB3, Sox9, Pax7, and Ki-67. In DNF/DPNF, expression of NRG1 correlated with pMEK and Pax7. mTOR correlated with pMEK, Sox9, and Pax7. Noteworthy, pMEK was weakly expressed in some DNF but not in DPNF. ErbB3 correlated with mTor and Ki-67. Furthermore, Rho correlated with Pax7 and Ki-67. In PNF, ErbB3 expression was associated with Sox9, mTOR, pMEK, and Pax7 as well as mTOR with Sox9 and Pax7, Rho with pMEK and Pax7, and pMEK with Pax7 and Sox9. In MPNST, only few correlations were observed, ErbB2 correlated with Ki-67, and Rho with pMEK.

Conclusion: Signaling networks of the RAS pathway could be retraced by correlation analysis of protein expression in subgroups of NF1 associated benign PNST. In regard to treatment of PNST, MEK inhibitors, which are presently evaluated for PNF, may possibly also be effective to some extent in DNF.