MUC1 alters oncogenic events and transcription in human breast cancer cells

INTRODUCTION: MUC1 is an oncoprotein whose overexpression correlates with aggressiveness of tumors and poor survival of cancer patients. Many of the oncogenic effects of MUC1 are believed to occur through interaction of its cytoplasmic tail with signaling molecules. As expected for a protein with oncogenic functions, MUC1 is linked to regulation of proliferation, apoptosis, invasion, and transcription. METHODS: To clarify the role of MUC1 in cancer, we transfected two breast cancer cell lines (MDA-MB-468 and BT-20) with small interfering (si)RNA directed against MUC1 and analyzed transcriptional responses and oncogenic events (proliferation, apoptosis and invasion). RESULTS: Transcription of several genes was altered after transfection of MUC1 siRNA, including decreased MAP2K1 (MEK1), JUN, PDGFA, CDC25A, VEGF and ITGAV (integrin α(v)), and increased TNF, RAF1, and MMP2. Additional changes were seen at the protein level, such as increased expression of c-Myc, heightened phosphorylation of AKT, and decreased activation of MEK1/2 and ERK1/2. These were correlated with cellular events, as MUC1 siRNA in the MDA-MB-468 line decreased proliferation and invasion, and increased stress-induced apoptosis. Intriguingly, BT-20 cells displayed similar levels of apoptosis regardless of siRNA, and actually increased proliferation after MUC1 siRNA. CONCLUSION: These results further the growing knowledge of the role of MUC1 in transcription, and suggest that the regulation of MUC1 in breast cancer may be more complex than previously appreciated. The differences between these two cell lines emphasize the importance of understanding the context of cell-specific signaling events when analyzing the oncogenic functions of MUC1, and caution against generalizing the results of individual cell lines without adequate confirmation in intact biological systems

On the di-1-naphthylcarbene-dibenzofluorene rearrangement and the ethylenization of diarylcarbinols

Solution-spray flash vacuum thermolysis of di-1-naphthyldiazomethane (9) results in the formation of dibenzo[c,g]fluorene (12), formed via a carbene- carbene rearrangement of di-1-naphthylcarbene (10). The isomeric dibenzo[α,i]fluorene (11) claimed by Franzen and Joschek (Liebigs Ann. Chem. 1960, 633, 7) is not formed, and no dibenzofluorene is formed on thermolysis in boiling naphthalene. 11 is formed on dehydration of di-1-naphthylcarbinol (14) with phosphoric acid, but the claimed tetra-1-naphthylethylene (13) is not formed, and the so-called ethylenization of diarylcarbinols is cast in doubt generally. The compound previously believed to be 13 is 13-[di(1- naphthyl)methyl]-dibenzo[α,i]fluorene (22). The alleged cleavage of 13 into two molecules of carbene 10 is unsubstantiated

MUC1 in human and murine mammary carcinoma cells decreases the expression of core 2 1,6-N-acetylglucosaminyltransferase and -galactoside 2,3-sialyltransferase

International audienceA good correlation between the expression of mucin1 (MUC1) and T antigen was found in breast cancer tumors and breast cancer cell lines, especially after treatment with neuraminidase. The association between the appearance of T antigen and the overexpression of MUC1 was further confirmed by transfecting MDA-MB-231 cells and murine 4T1 mammary carcinoma cells with cDNA for MUC1 and using an RNAi approach to inhibit the expression of MUC1 gene in T47D cells. Furthermore, we discovered that in 4T1 cells which express the sialyl Le(X) antigen, overexpression of MUC1 caused not only appearance of T antigen, but also loss of the sialyl Le(X) structure. As the observed changes in O-glycan synthesis can be associated with changes in the expression of specific glycosyltransferases, core 1 β1,3-galactosyltransferase, core 2 β1,6-N-acetylglucosaminyltransferase (C2GnT1) and β-galactoside α2,3-sialyltransferase (ST3Gal I), we studied their expression in parental, vector-transfected and MUC1-transfected MDA-MB-231 and 4T1 cells as well as T47D cells transduced with small hairpin RNA targeted MUC1 mRNA. It was found that the expression of C2GnT1 and ST3Gal I is highly decreased in MUC1-expressing MDA-MB-231 and 4T1 cells and increased in T47D cells with suppressed expression of MUC1. Therefore, we found that changes in the structure of O-linked oligosaccharides, resulting in the occurrence of T antigen, are at least partially associated with MUC1 overexpression which down-regulates the expression of C2GnT1 and ST3Gal I. We showed also that the overexpression of MUC1 in 4T1 cells changes their adhesive properties, as MUC1-expressing cells do not adhere to E-selectin, but bind galectin-3