Sodium butyrate (NaBu) was shown to induce differentiation and apoptosis in the human pancreatic cancer cell line AsPC-1. A suppression subtractive hybridization-based technique was used to identify genes induced by NaBu. A novel cDNA was found to be highly up-regulated in AsPC-1 cells in response to NaBu. The gene expresses a 1.65-kb mRNA encoding a protein with an open reading frame of 422 amino acids. It has an intermediate filament signature sequence and extensive homology to type I keratins. Sequence comparison with known keratins indicated that the gene shares 42-46% amino acid identity and 60-65% similarity within the alpha-helical rod domain. The gene is named K23 (for human type I Keratin 23, KRT23). K23 mRNA was highly induced by NaBu in different pancreatic cancer cells. Trichostatin A (TSA), a potent and specific inhibitor of histone deacetylase, similarly induced K23 mRNA expression. Treatment with either actinomycin D or cycloheximide efficiently blocked the induction of K23 mRNA by NaBu/TSA. These results indicate that K23 mRNA induction by NaBu or TSA is a downstream event of histone hyperacetylation. We also demonstrated that expression of p21(WAF1/CIP1) antisense RNA efficiently blocked the induction of K23 mRNA induced by NaBu. Our results suggest that K23 is a novel member of the acidic keratin family that is induced in pancreatic cancer cells undergoing differentiation by a mechanism involving histone hyperacetylation. p21(WAF1/CIP1) serves as an important mediator during the induction process of K23 by NaBu.
Copyright 2000 Wiley-Liss, Inc.