Cellular distribution of cholesterogenesis-linked, phosphoisoprenylated proteins in proliferating cells

Abstract

A set of isoprenylated proteins has been detected in rapidly proliferating, suspension-grown murine lymphoma cells. Our evidence indicates that all of these isoprenylated proteins are phosphorylated. Subsequent to a 24 h incubation with mevinolin to deplete the intracellular mevalonate (MVA) level, cells were incubated with [3H]MVA and/or 32Pi and both total cell and subcellular fraction proteins were resolved via 1- and 2-D gel electrophoresis, then assessed via subsequent autoradiography. The phospho-isoprenylated proteins comprise a set spanning a molecular mass range of 21-69 kDa and all dispay acidic pI. MVA-derivatized proteins of 21-24 kDa, which consist of multiple isoforms, are present in both cytosolic and nuclear fractions. Larger phospho-isoprenylated protein species (44-69 kDa) are specifically localized within the nucleus, where applicable extraction protocols indicate that they are part of or closely affiliated with the nuclear matrix-intermediate filament (NM-IF) components. The localization of the 69 kDa prenylated species within the NM-IF fraction, together with evidence of its phosphorylation, supports recent indications that this protein is the nuclear matrix component lamin B.