New function for NF1 tumor suppressor

The expression and subcellular localization of neurofibromatosis type 1 tum or suppressor was studied in keratinocytes induced to differentiate by incr eased Ca2+ concentration of the culture medium. Differentiating keratinocyt es became intensely immunoreactive for neurofibromatosis type 1 protein, wh ich was apparently associated with cellular fibrils. Double immunolabeling with antibodies to cytokeratin 14 and neurofibromatosis type 1 protein sugg ested an association of intermediate type cytoskeleton and neurofibromatosi s type 1 protein. The presence of neurofibromatosis type 1 protein in cell preparations treated with cytoskeletal buffer indicated a high affinity int eraction between intermediate filaments and neurofibromatosis type 1 protei n. Further studies utilizing double immunolabelings revealed that the inten se neurofibromatosis type 1 tumor suppressor signal on intermediate filamen ts was temporally limited to the period in keratinocyte differentiation in which the formation of desmosomes takes place. Keratinocytes were also cult ured from nine patients with type 1 neurofibromatosis and were studied with respect to cell morphology, and association of neurofibromatosis type 1 pr otein with intermediate cytoskeleton. The results showed that keratinocytes cultured from patients with neurofibromatosis type 1 displayed a highly va riable cell size and morphology compared to controls. The latter findings r epresent predicted alterations in a situation where cytoskeletal organizati on is disturbed. Furthermore, differentiating neurofibromatosis type 1 kera tinocytes were characterized by a reduced number of cytokeratin bundles tha t were decorated neurofibromatosis type 1 protein. The results of this stud y suggest that neurofibromatosis type 1 tumor suppressor exerts its effects in part by controlling organization of cytoskeleton during the formation o f cellular contacts.