RAS-ASSOCIATED NUCLEAR STRUCTURAL-CHANGE APPEARS FUNCTIONALLY SIGNIFICANT AND INDEPENDENT OF THE MITOTIC SIGNALING PATHWAY

An altered nuclear morphology has been previously noted in association with Ras activation, but little is known about the structural basis, functional significance, signaling pathway, or reproducibility of any such change. We first tested the reproducibility of Ras-associated nuc lear change in a series of rodent fibroblast cell lines. After indepen dently developing criteria for recognizing Ras-associated nuclear chan ge in a Papan icolaou stained test cell line with an inducible H(T24)- Ras oncogene, two cytopathologists blindly and independently assessed 17 other cell lines. If the cell lines showed Ras-associated nuclear c hange, a rank order of increasing nuclear change was independently sco red. Ras-associated nuclear changes were identified in v-Fes, v-Src, v -Mos, v-Raf, and five of five H(T24)-Ras transfectants consisting of a change from a flattened, occasionally undulating nuclear shape to a m ore rigid spherical shape and a change from a finely textured to a coa rse heterochromatic appearance. Absent or minimal changes were scored in six control cell lines. The two cytopathologists' independent morph ologic rank orders were similar(P<.0002). The mitogen signaling pathwa y per se does not appear to transduce the change since no morphologic alterations were identified in cell lines with activations of downstre am components of this pathway-MAPKK or c-Myc-and the rank orders did n ot correlate with markers of mitotic rate (P >.11). The rank order cor related closely with metastatic potential (P <.0014 and P <.0003) but not with histone H1 composition or global nuclease sensitivity. Based on published studies of five of the cell lines, there may be a correla tion between increases in certain nuclear matrix proteins and the Ras- associated nuclear change. (C) 1998 Wiley-Liss, Inc.