RNP complexes containing hnRNP L, A1, and M associate with CEACAM1 mRNA. (A-B) Quantitative RT-PCR of immunoprecipitated CEACAM1-L and CEACAM1-S mRNA. Primers were designed to either detect the presence or absence of exon 7, as shown above each figure. The average CEACAM1 mRNA fold enrichment is shown above each antibody (histogram) tested. (C) Model for the role of IRF-1 in coupling transcription and AS. In breast carcinoma epithelial cells default splicing maintains production of CEACAM1-S. When IRF-1 binds to its cognate ISRE sequence, the transcriptional complex communicates with the splicing machinery (denoted with <->) via uncharacterized interactions through splicing regulators leading to an AS switch and production of CEACAM1-L.