21. The steroid hormone glucocorticoid can enter cells and bind with glucocorticoid receptor (GR) to regulate gene expression. Which is incotrect?
(A) GR is in the cytoplasm in the absence of glucocorticoid.
(B) GR is a leucine-zipper-containing transcription factor.
(C) Glucocorticoid-bound GR can form a homodimer to bind to GREs.
(D) GR serves as a transcription activator or inhibitor depending on the gene context.
(E) GR inhibits the expression of cytokine genes by tethering other transcription factors such as AP1 and NF-kB.