The non-␤ -oxidisable tetradecylthioacetic acid (TTA) is incorporated into cellular membranes when C3H/ 10T1/2 cells are cultured in TTA-containing medium. We here demonstrate that this alteration in cellular membranes affect the nuclear translocation of proteins involved in signal transduction. Analysis of cellular fatty acid composition shows that TTA and TTA:1n-8 constitute approximately 40 mol% of total fatty acids in cellular/nuclear membranes. Activation of c-fos expression is significantly inhibited in TTA-treated cells but the enzymatic activation of mitogen activated protein kinase (ERK) is not affected. Immunofluorescence and confocal microscopy studies demonstrate that in mitogene-stimulated TTA-treated cells, the translocation of phosphorylated ERK1/2, protein kinase C ␣ (PKC ␣ ), and PKC ␤ 1 from the cytoplasm into the nucleus is considerably decreased and delayed. Concomitant with a decreased nuclear import, ERK1/2 dephosphorylation is decreased in TTA-treated cells. There is no TTA-induced inhibition of nuclear import of proteins with a classical nuclear localization signal (NLS), as seen by in vitro nuclear import experiments of BSA fused to the NLS from SV40 large T, or in vivo studies of hnRNP A1 nuclear import. The expression levels of Importin ␣ , Importin ␤ , Importin 7, and NTF2 are not altered in the TTA-treated cells. Taken together, our data indicate that TTA treatment causes changes in cellular fatty acid composition that negatively affect NLS-independent mechanisms of protein translocation through the nuclear pore complex. -Bjørndal, B., C. Helleland, S-O. Bøe, O. A. Gudbrandsen, K-H. Kalland, P. Bohov, R. K. Berge, and J. R. Lillehaug. Nuclear import of factors involved in signaling is inhibited in C3H/10T1/2 cells treated with tetradecylthioacetic acid.

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