REGULATION OF CCAAT ENHANCER BINDING-PROTEIN ISOFORMS BY SERUM AND GLUCOCORTICOIDS IN THE RAT INTESTINAL EPITHELIAL CRYPT CELL-LINE IEC-6/

Members of the CCAAT/enhancer binding protein (C/EBP) gene family are expressed in murine intestine. However, Little is known about their re gulation in intestinal epithelial cells. In an attempt to determine re gulatory mechanisms involved in their expression, we examined C/EBP al pha, beta, and delta isoform expression in response to serum and gluco corticoids in the rat intestinal epithelial crypt-derived cell line IE C-6, by Northern blot, transcription run-on assays, indirect immunoflu orescence, Western blot, and electrophoretic mobility shift assays. Se rum leads to rapid and transient increases in C/EBP alpha and beta mRN A and protein levels by posttranscriptional regulatory mechanisms, wit hout affecting transcriptional initiation, However, C/EBP-specific DNA binding capacity is not affected by serum. Whereas C/EBP alpha expres sion is not regulated by glucocorticoids, C/EBP beta and delta mRNA an d protein levels are rapidly induced. These inductions result hom both increased transcription rates and posttranscriptional regulatory mech anisms as well, Moreover, C/EBP beta and delta containing DNA binding complexes are increased by glucocorticoids as determined by supershift assays, in contrast to C/EBP alpha containing complexes. Immunofluore scence studies show cytoplasmic and nuclear localization for C/EBP alp ha, in contrast to a restricted nuclear localization for both C/EBP be ta and C/EBP delta. These results confirm C/EBP isoforms expression in intestinal epithelial cells. Differential regulation by serum and glu cocorticoids as well as different localization of three C/EBP isoforms suggest a role for this class of transcription factors in the control of gene expression in intestinal epithelial cells. (C) 1996 Academic Press, Inc.