c-Jun Potentiates the Functional Interaction between the Amino and Carboxyl Termini of the Androgen Receptor

Abstract

The transactivation functions of the human androgen receptor (hAR) are regulated by several accessory factors that can be either positive or negative. One factor that has been previously shown to mediate hAR transactivation is the proto-oncoprotein c-Jun. The positive effect is a primary one, can be exerted by both endogenous and exogenous c-Jun, and requires multiple regions of c-Jun. However, the exact mechanism by which c-Jun exerts its enhancing function is unknown. In this study, we have used a mammalian two-hybrid system to ask if c-Jun influences the ligand-dependent amino-to carboxyl-terminal (N-to-C) interaction of hAR, which is thought to be responsible for the homodimerization of this receptor. Our results show that c-Jun enhances both hAR N-to-C terminal interaction and DNA binding in vitro. We have also tested a panel of c-Jun and c-Fos mutants for their activities on the N-to-C interaction, and the data demonstrate that the activities of these mutants parallel their activities on hAR transactivation. A mutation in the hAR activation function-2 (AF-2) abrogates N-to-C interaction, DNA binding, and transactivation, and these activities are not rescued by exogenous c-Jun. Interestingly, the p160 coactivator TIF2 can stimulate hAR N-to-C interaction, a finding consistent with the effect on hAR transactivation. These data strongly suggest that the hAR N-to-C interaction is the target of c-Jun action, and this activity requires a functional receptor AF-2.

c-Jun enhancement of androgen receptor transactivation is associated with prostate cancer cell proliferation

“…In contrast, expression of antisense c-Jun had a negative effect. These transcription results are completely consistent with our earlier data using transient transfection experiments (Bubulya et al, 1996(Bubulya et al, , 2000(Bubulya et al, , 2001Tillman et al, 1998;Wise et al, 1998) and strongly suggest that endogenous levels of c-Jun in LNCaP cells are both required and limiting for androgen-regulated gene expression. Although it is not known how widespread the involvement of c-Jun coactivation on the expression of androgen-regulated genes is, it is important to note that all three androgen target genes analysed in this study appear to be regulated by c-Jun coactivation.…”

“…This separation of AR coactivation from AP-1 transactivation has been demonstrated in a variety of cell lines, including Cos (Bubulya et al, 2001), androgen-dependent and -independent LNCaP, and AR-expressing PC-3 cells. In addition, c-Fos strongly stimulates cJun's transactivation properties but represses its coactivation of AR (Tillman et al, 1998).…”

“…These results together strongly suggest that the transactivation and coactivation functions of c-Jun are distinct and thus may operate via different mechanisms. More recently, we have published that c-Jun can mediate AR N-to-C interaction and thereby enhance DNA binding (Bubulya et al, 2001), an ability that is also observed with other AR coactivators, including SRC-1, TIF2, and CBP (Ikonen et al, 1997).…”

“…To make c-Jun(Ala63/73)/pCI-Neo, c-Jun(Ala63/73)/RSV (Bubulya et al, 2001) was digested with BsaAI and StyI and filled in with DNA polymerase klenow fragment. This fragment was then inserted into EcoRV-digested pTRE2 to get c-Jun(Ala63/73)/pTRE2.…”

“…While c-Jun represses the transcriptional activity of the AR-related glucocorticoid receptor (GR) (Schule et al, 1990), as well as other nuclear receptors (reviewed in Pfahl, 1993), it strongly potentiates ARmediated transcription (Shemshedini et al, 1992;Bubulya et al, 1996). Several studies from our lab have characterized this coactivator function of c-Jun on AR (Bubulya et al, 1996(Bubulya et al, , 2000(Bubulya et al, , 2001Tillman et al, 1998;Wise et al, 1998). Perhaps the most intereting finding is that c-Jun's function as coactivator can be separated from that of a transactivator, as a transactivationdeficient mutant, c-Jun(Ala63/73), is still active in coactivation (Wise et al, 1998).…”