HEAT-INDUCED MORPHOLOGICAL AND BIOCHEMICAL-CHANGES IN THE NUCLEAR LAMINA FROM EHRLICH ASCITES TUMOR-CELLS IN-VIVO

Membrane-depleted nuclei from Ehrlich ascites tumor (EAT) cells isolat ed at low ionic strength in the presence of EDTA exhibit highly decond ensed chromatin fibers and a loss of morphologically identifiable nucl eoli. Treatment of these nuclei with nucleases and 2 M NaCl followed b y low-speed centrifugation permitted the facile isolation of the nucle ar lamina layer. Under the same conditions, but after heat-shock treat ment of the living cells, the chromatin appears in a more condensed st ate, the nucleoli are well-defined, and the nuclear lamina layer was d estabilized in concert with the appearance of an internal nuclear matr ix and nucleolar skeleton. Furthermore, we also found both an increase in the protein mass as well as the appearance of a relatively large n umber of new proteins in this fraction, which are phosphorylated. The major proteins of the nuclear lamina, the lamins, and the residual vim entin remained insoluble. These heat-shock-induced changes were also a ccompanied by a dephosphorylation of lamins A and C but not of lamin B . (C) 1993 Wiley-Liss, Inc.