Change in the expression of a nuclear matrix-associated protein is correlated with cellular transformation

We have identified a monoclonal antibody that recognizes a nuclear matrix-associated protein in NIH 3T3 cells. The immunofluorescence pattern consists predominantly of bright nuclear granule clusters distributed throughout the nucleoplasm, with the exclusion of nucleoli. It recognizes a protein of 190 kDa that is down-regulated to various degrees in a panel of single-oncogene-transformed NIH 3T3 cells. Its localization is similar, but not identical, to the spliceosomal speckles. p190 shows a coordinate expression during the growth cycle of nontransformed NIH 3T3 cells; it is synthesized at the highest level under growth arrest conditions. It is expressed in adult mouse brain and is also present in human IMR-90 fibroblasts.