RESUMO
Anomalous expression of certain types of mucins occurs in pancreatic tumors, but little is known about the causes. MUC2 and MUC5AC are not expressed in normal pancreas. In the present study an immunohistochemical screening showed that MUC2 antigen was expressed in 6% of invasive tumors. Of the pancreatic cell lines, 2.4% expressed MUC2 message and antigen. In contrast, MUC5AC antigen was expressed in 86-100% of invasive adenocarcinoma (depending on the antibody). MUC5AC message and antigen were expressed in 66.7% of the cell lines tested. A polymerase chain reaction based assay was used to determine if methylation of CpG sites immediately 5' of the transcription initiation sites of the MUC2 and MUC5AC genes could be related to mucin expression in the cell lines. Digestibility by the methylation sensitive restriction enzyme HpaII correlated with the presence or absence of mRNA in 100% and 77.8% of the cell lines for MUC2 and MUC5AC, respectively. Treatment of a cell line that did not express MUC2 or MUC5AC gene products with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine resulted in an increase in MUC2 message but no change in MUC5AC message. In summary, the expression of MUC2 gene products correlated well with methylation of the proximal region of the promoter whereas expression of MUC5AC may involve additional regions or other mechanisms.
Assuntos
Adenocarcinoma Mucinoso/patologia , Adenocarcinoma/patologia , Azacitidina/análogos & derivados , Metilação de DNA , DNA de Neoplasias/química , Regulação Neoplásica da Expressão Gênica , Mucinas/genética , Proteínas de Neoplasias/genética , Neoplasias Pancreáticas/patologia , Regiões Promotoras Genéticas , Adenocarcinoma/genética , Adenocarcinoma Mucinoso/genética , Azacitidina/farmacologia , Sequência de Bases , DNA (Citosina-5-)-Metiltransferases/antagonistas & inibidores , Metilação de DNA/efeitos dos fármacos , DNA de Neoplasias/genética , Decitabina , Inibidores Enzimáticos/farmacologia , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Dados de Sequência Molecular , Mucina-5AC , Mucina-2 , Mucinas/biossíntese , Invasividade Neoplásica , Proteínas de Neoplasias/antagonistas & inibidores , Proteínas de Neoplasias/biossíntese , Pâncreas/metabolismo , Neoplasias Pancreáticas/genética , Regiões Promotoras Genéticas/genética , RNA Mensageiro/biossíntese , RNA Neoplásico/biossínteseRESUMO
MUC5AC mucin is not expressed in normal pancreas but is expressed in tumors. Little is known about the mechanisms that lead to this atypical expression. In this study, we demonstrate that stimulation of adenylyl cyclase and the protein kinase A (PKA) pathway by forskolin and vasoactive intestinal peptide (VIP) increased MUC5AC antigen expression and release from pancreatic cancer cells. Stimulation of the PKA pathway also increased MUC5AC mRNA. When SW1990 pancreatic cancer cells were grown on porous membranes they released MUC5AC mucins apically in response to VIP (10(-7) M) applied to their basolateral surfaces. SW1990 cells, as have been reported for other pancreatic cancer cells, have high affinity (<10(-7) M) VIP receptors and low affinity (>10(-6) M) secretin receptors. We also showed that four antibodies (CLH2, 21M1, 45M1, and Nd2) react with MUC5AC antigen in different cellular compartments of both tissues and cultured cells. In conclusion, the PKA pathway may contribute to the up-regulation of MUC5AC expression seen in pancreatic tumors.