Charge heterogeneity in wildtype and variant glucocorticoid receptors

Abstract

Two-dimensional electrophoresis was used to examine charge heterogeneity in glucocorticoid receptors (GCRs) from sublines of the thymic-derived, mouse P1798 lymphosarcoma which were sensitive (S) or resistant (R) to glucocorticoid-mediated apoptosis. Previous work had identified the 97 kDa wildtype GCR (WT-GCR) in S cells and two variant GCRs in R cells: a 45 kDa, steroid-binding truncated GCR (TR-GCR), and a 97 kDa non steroid-binding GCR (NSB-GCR). Using denaturing isoelectric focusing, we now show that S cells as well as adult mouse thymus gland also express the NSB-GCR at pI 5.6 in addition to the WT-GCR which resolves between pH 5.9–7.1. Thus, the NSB-GCR is detected in steroid-sensitive cells and is not unique to R cells. Separation of receptors by native isoelectric focusing suggested that the TR-GCR in R cells resolved at a single, high pI (8.1) relative to the WT-GCR which resolved in a broad range (pI 5.8–8.0). The high pI of the TR-GCR may alter its functional activity thereby contributing to the resistance phenotype.