Transformed mouse glucocorticoid receptor: generation and interconversion of the 3.8S, monomeric and 5.2S, oligomeric species

Recent studies have implicated subunit dissociation as a possible mechanism of glucocorticoid receptor transformation Vedeckis, W.V. (1983) Biochemistry 22, 1983-1989; Raaka, B.M., & Samuels, H.H. (1983) J. Biol. Chem. 258, 417-425]. While it is becoming increasingly evident that the untransformed (non-nuclear-binding and non-DNA-binding) glucocorticoid receptor from mouse AtT-20 cells is a 9.1S oligomeric species (Mr 290 000-360 000), two transformed species have been described for this receptor. One of these has a sedimentation coefficient of 5.2 S (on molybdate-containing gradients), while the smallest nonproteolyzed, monomeric subunit is 3.8 S. The present study was undertaken to determine which is the most common form generated both in vitro and in vivo and the structural relationship between these two forms. A wide variety of in vitro transformation protocols all yielded the 5.2S form when analyzed on molybdate-containing sucrose gradients by using a vertical tube rotor. Kinetic studies showed that the appearance of the 5.2S form coincided precisely with the appearance of transformed receptor, as defined by DEAE-cellulose elution. Furthermore, when the 3.8S and 5.2S peaks were collected from sucrose gradients directly, they were transformed receptors as defined by both DEAE-cellulose and DNA-cellulose chromatography, while the 9.1S sucrose gradient peak was untransformed when the same criteria were used. The 3.8S monomer, when isolated from high-salt sucrose gradients and then desalted, reverted to the 5.2S form (molybdate-containing gradients) or a 6.6S form (low-salt, molybdate-free gradients).(ABSTRACT TRUNCATED AT 250 WORDS)