The glycoprotein mucin-1 negatively regulates GalNAc transferase 5 expression in pancreatic cancer.

Aberrant expression of the glycoprotein mucin-1 (MUC1) has been associated with pancreatic cancer progression and metastasis as a result of mediating the oncogenic transcriptional regulation of target genes. In the present study, we demonstrate that MUC1 downregulates the expression of the tumor suppressor polypeptide N-acetylgalactosaminyltransferase 5 in pancreatic cancer. ChIP-on-chip analysis revealed that the MUC1 cytoplasmic tail binds to regulatory elements in the GALNT5 gene. Additionally, MUC1 increases binding of p53 and c-Jun and decreases the binding of Sp1 to the proximal promoter and exonic regions of GALNT5. We also observed that expression of N-acetylgalactosaminyltransferase 5 is inversionally proportional to MUC1 expression in human pancreatic cancer. These results demonstrate that MUC1 downregulates the expression of N-acetylgalactosaminyltransferase 5 in pancreatic cancer by modifying the promoter occupancy of transcription factors through its cytoplasmic domain.

MUC1 regulates expression of multiple microRNAs involved in pancreatic tumor progression, including the miR-200c/141 cluster.

MUC1 is a transmembrane glycoprotein that modulates transcription via its cytoplasmic domain. We evaluated the capacity of MUC1 to regulate the global transcription of microRNAs in pancreatic cancer cells expressing MUC1. Results indicated that MUC1 regulated expression of at least 103 microRNAs. We evaluated further regulation of the microRNA transcript cluster miR-200c/141, which was among the most highly regulated microRNAs. We found that MUC1 directly interacted with ZEB1, a known transcriptional repressor of the miR-200c/141 cluster, at the promoter of miR-200c/141, and further reduced transcript production. These data indicate that signaling through MUC1 influences cancer progression by regulating transcription of microRNAs that are associated with the process of metastasis.

MUC1 mucin stabilizes and activates hypoxia-inducible factor 1 alpha to regulate metabolism in pancreatic cancer.

Aberrant glucose metabolism is one of the hallmarks of cancer that facilitates cancer cell survival and proliferation. Here, we demonstrate that MUC1, a large, type I transmembrane protein that is overexpressed in several carcinomas including pancreatic adenocarcinoma, modulates cancer cell metabolism to facilitate growth properties of cancer cells. MUC1 occupies the promoter elements of multiple genes directly involved in glucose metabolism and regulates their expression. Furthermore, MUC1 expression enhances glycolytic activity in pancreatic cancer cells. We also demonstrate that MUC1 expression enhances in vivo glucose uptake and expression of genes involved in glucose uptake and metabolism in orthotopic implantation models of pancreatic cancer. The MUC1 cytoplasmic tail is known to activate multiple signaling pathways through its interactions with several transcription factors/coregulators at the promoter elements of various genes. Our results indicate that MUC1 acts as a modulator of the hypoxic response in pancreatic cancer cells by regulating the expression/stability and activity of hypoxia-inducible factor-1α (HIF-1α). MUC1 physically interacts with HIF-1α and p300 and stabilizes the former at the protein level. By using a ChIP assay, we demonstrate that MUC1 facilitates recruitment of HIF-1α and p300 on glycolytic gene promoters in a hypoxia-dependent manner. Also, by metabolomic studies, we demonstrate that MUC1 regulates multiple metabolite intermediates in the glucose and amino acid metabolic pathways. Thus, our studies indicate that MUC1 acts as a master regulator of the metabolic program and facilitates metabolic alterations in the hypoxic environments that help tumor cells survive and proliferate under such conditions.

Cyclin-dependent kinase 5 is amplified and overexpressed in pancreatic cancer and activated by mutant K-Ras.

PURPOSE: To evaluate the nature of cyclin-dependent kinase 5 (CDK5) hyperactivity in pancreatic cancer progression. EXPERIMENTAL DESIGN: We used genetic, biochemical, and molecular biology methods to investigate the nature and function of overexpression of CDK5 and its activators p35 and p39 during the progression of pancreatic cancer. RESULTS: Amplification of the CDK5 gene or either of its main activators, p35 and p39, was observed in 67% of human pancreatic ductal adenocarcinoma (PDAC). CDK5, p35, and p39 were rarely expressed in pancreatic ducts whereas more than 90% of PDACs had increased levels of CDK5 and p35. Increased levels of CDK5, p35, and p39 protein were observed in several pancreatic cancer cell lines. Inhibition of CDK5 kinase activity using a CDK5 dominant-negative mutant or the drug roscovitine significantly decreased the migration and invasion of pancreatic cancer cells in vitro. Increased CDK5 kinase activity was also observed in immortalized human pancreatic nestin-expressing (HPNE) cells expressing a mutant form of K-Ras (G12D) compared with HPNE cells expressing native K-Ras. G12D K-Ras increased cleavage of p35 to p25, a stable and greater activator of CDK5, thus implicating a role for CDK5 in early progression of PDAC. Inhibition of the signaling cascade downstream of mutant K-Ras (G12D) that involves mitogen-activated protein/extracellular signal-regulated kinase, phosphoinositide 3-kinase, or CDK5 decreased p25 protein levels. CONCLUSION: These results suggest that mutant K-Ras acts in concert with CDK5 and its activators to increase malignant progression, migration, and invasion of pancreatic cancer cells.