The human MUC1 gene expresses at least 2 type 1 membrane proteins: MUC1/REP, a polymorphic high m.w. MUC1 glycoprotein often highly expressed in breast cancer tissues and containing a variable number of tandem 20 amino acid repeat units, and the MUC1/Y protein, which lacks this repeat array and, therefore, is not polymorphic. Despite their documented importance in signal transduction processes, the relative expression of the 2 isoforms in epithelial tumors is unknown. Using antibody reagents which recognize different MUC1 domains, the expression of these isoforms in malig The MUC1 gene is frequently expressed with high intensity in human carcinomas, especially in breast cancer tissue (Ceriani et al., 1977;Burchell et al., 1987). In these patients, augmented concentrations of MUC1 proteins (previously referred to as episialin, H23Ag; ETA, epithelial tumor antigen; PEM, polymorphic epithelial mucin; EMA, epithelial membrane antigen; CA15-3; MCA, mammary carcinoma antigen) may be one of the earliest signs of disease progression, and, as such, the MUC1 gene has aroused much interest. A major MUC1 gene product (designated MUC1/ REP) is a polymorphic type 1 transmembrane molecule which consists of a large, heavily glycosylated extracellular domain, a transmembrane domain and a 72 amino acid cytoplasmic tail Hareuveni et al., 1990;Ligtenberg et al., 1990;Gendler et al., 1990). This isoform is proteolytically cleaved early after translation (Ligtenberg et al., 1992a) and is shed from the cell by an unknown mechanism. The MUC1 isoform, MUC1/Y, generated by alternative splicing (Zrihan-Licht et al., 1994b), has a molecular mass of 42-45 kDa and, in contrast to MUC1/REP, does not undergo proteolytic cleavage (Zrihan-Licht et al., 1994b). Furthermore, this novel MUC1 isoform retains the N-terminal as well as the transmembrane and cytoplasmic MUC1 domains but lacks the tandem repeat array that has been considered the hallmark of MUC1.To date, the relative extent of expression in epithelial tumors of the MUC1 protein containing the tandem repeat array vs. that of the novel isoform devoid of the tandem repeats has not been studied. To address this issue, we determined the expression of MUC1 gene products in epithelial tumors using not only a panel of antibodies directed against the 20 amino acid tandem repeat motif but also antibodies which specifically recognize the MUC1/Y cytoplasmic and extracellular domains. Reverse transcriptase PCR (RT-PCR) was used to assess the expression of MUC1 isoforms devoid of the tandem repeat array. Our studies demonstrate that the MUC1 isoforms lacking the tandem repeat array not only are extensively expressed in epithelial tumors but in certain cases they are almost the only MUC1 protein products observed.Significantly, the tyrosine and, to a lesser extent, the serine residues of the cytoplasmic domains of the MUC1 proteins undergo phosphorylation (Zrihan-Licht et al., 1994a). One study confirmed the phosphorylation of the MUC1 tyrosine residues (Pandey et al., 1995) and demonstrated in vivo ...

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The human MUC1 gene expresses at least 2 type 1 membrane proteins: MUC1/REP, a polymorphic high m.w. MUC1 glycoprotein often highly expressed in breast cancer tissues and containing a variable number of tandem 20 amino acid repeat units, and the MUC1/Y protein, which lacks this repeat array and, therefore, is not polymorphic. Despite their documented importance in signal transduction processes, the relative expression of the 2 isoforms in epithelial tumors is unknown. Using antibody reagents which recognize different MUC1 domains, the expression of these isoforms in malig The MUC1 gene is frequently expressed with high intensity in human carcinomas, especially in breast cancer tissue (Ceriani et al., 1977;Burchell et al., 1987). In these patients, augmented concentrations of MUC1 proteins (previously referred to as episialin, H23Ag; ETA, epithelial tumor antigen; PEM, polymorphic epithelial mucin; EMA, epithelial membrane antigen; CA15-3; MCA, mammary carcinoma antigen) may be one of the earliest signs of disease progression, and, as such, the MUC1 gene has aroused much interest. A major MUC1 gene product (designated MUC1/ REP) is a polymorphic type 1 transmembrane molecule which consists of a large, heavily glycosylated extracellular domain, a transmembrane domain and a 72 amino acid cytoplasmic tail Hareuveni et al., 1990;Ligtenberg et al., 1990;Gendler et al., 1990). This isoform is proteolytically cleaved early after translation (Ligtenberg et al., 1992a) and is shed from the cell by an unknown mechanism. The MUC1 isoform, MUC1/Y, generated by alternative splicing (Zrihan-Licht et al., 1994b), has a molecular mass of 42-45 kDa and, in contrast to MUC1/REP, does not undergo proteolytic cleavage (Zrihan-Licht et al., 1994b). Furthermore, this novel MUC1 isoform retains the N-terminal as well as the transmembrane and cytoplasmic MUC1 domains but lacks the tandem repeat array that has been considered the hallmark of MUC1.To date, the relative extent of expression in epithelial tumors of the MUC1 protein containing the tandem repeat array vs. that of the novel isoform devoid of the tandem repeats has not been studied. To address this issue, we determined the expression of MUC1 gene products in epithelial tumors using not only a panel of antibodies directed against the 20 amino acid tandem repeat motif but also antibodies which specifically recognize the MUC1/Y cytoplasmic and extracellular domains. Reverse transcriptase PCR (RT-PCR) was used to assess the expression of MUC1 isoforms devoid of the tandem repeat array. Our studies demonstrate that the MUC1 isoforms lacking the tandem repeat array not only are extensively expressed in epithelial tumors but in certain cases they are almost the only MUC1 protein products observed.Significantly, the tyrosine and, to a lesser extent, the serine residues of the cytoplasmic domains of the MUC1 proteins undergo phosphorylation (Zrihan-Licht et al., 1994a). One study confirmed the phosphorylation of the MUC1 tyrosine residues (Pandey et al., 1995) and demonstrated in vivo ...

The nature of the intraterrninal compartments from which acetylchohne (ACh) is released following presynaptic stimulation was investigated. This was pursued by examining the effects of the anticholinergic drug 2-(4-phenylpiperidino)cyclohexanol (AH5183) on the release of newly synthesized [-'H]ACh and of endogenous ACh from puritied cholinergic nerve terminals (synaptosomes) which were isolated from the electric organs of Torpedo. Preincubation of the synaptosomes, with AH5183 (l-10 pM), does not affect either the intraterminal synthesis of [JH]ACh or the uptake of its precursors, but results in a marked inhibition (85%) of the release of the newly synthesized ['H]ACh. However, when AH5 183 is added following the accumulation of [3H]ACh in the nerve terminals, it does not affect [)H]ACh release. AH5183 also has no effect on the release of preformed endogenous ACh. These findings, together with the previous in vitro demonstrations that AH5183 is a potent inhibitor of ACh uptake into isolated cholinergic vesicles, suggest that most of the synaptosomal ACh is secreted by a vesicular mechanism. AcetylchoIine Cholinergic synaptic vesicle

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