Amino Acid Residues Required for Physical and Cooperative Transcriptional Interaction of STAT3 and AP-1 Proteins c-Jun and c-Fos

Abstract

Cooperation between STAT3 and c-Jun in driving transcription during transfection of reporter constructs is well established, and both proteins are present on some interleukin-6 (IL-6) STAT3-dependent promoters on chromosomal loci. We report that small interfering RNA knockdown of c-Jun or c-Fos diminishes IL-6 induction of some but not all STAT3-dependent mRNAs. Specific contact sites in STAT3 responsible for interaction of a domain of STAT3 with c-Jun were known. Here we show that the B-zip domain of c-Jun interacts with STAT3 and that c-Jun mutation R261A or R261D near but not in the DNA binding domain blocks in vitro STAT3-c-Jun interaction and decreases costimulation of transcription in transfection assays. Cooperative binding to DNA of tyrosine-phosphorylated STAT3 and both wild-type and R261A mutant c-Jun was observed. Even c-Jun mutant R261D, which on its own did not bind DNA, bound DNA weakly in the presence of STAT3. We conclude that a functional interaction between STAT3 and c-Jun while bound to chromosomal DNA elements exists and is necessary for driving transcription on at least some STAT3 target genes. Identifying such required interactive protein interfaces should be a stimulus to search for compounds that could ultimately inhibit the activity of STAT3 in tumors dependent on persistently active STAT3.

This work was supported by NIH grants (AI34420 and AI32489) to James E. Darnell, Jr. and GM068566 to Xiaomin Chen. Michael Ginsberg's support is from NIH training grant T32 CA09673. Zhiyong Ren is supported by the Odyssey Program and the Cockrell Foundation Award for Scientific Achievement at the University of Texas M. D. Anderson Cancer Center.