RESUMO
OBJECTIVES: Sialyl-Tn (sTn) is a mucin carbohydrate-associated antigen that is strongly expressed in a large number of colorectal carcinomas. In this study, we combined immunohistochemical and enzymatic techniques in order to find the correlation between sTn tissue expression and the sialyltransferase activity (ST6GalNAc I) responsible for its synthesis in colorectal cancer (CRC) patients. METHODS: We compared sTn expression in healthy (n = 46), tumorous (n = 60) and transitional tissue (n = 46) from CRC patients, and correlated sTn altered expression with clinicopathologic variables of the patient. Furthermore, we determined ST6GalNAc I tissue activity employing asialo-ovine submaxillary mucin (asialo-OSM) as glycoprotein acceptor (n = 27). RESULTS: The rates of sTn positive expression obtained for healthy, tumorous and transitional tissues were 15, 67 and 63%, respectively. These rates led to statistically significant differences between healthy and tumorous or transitional tissue (p = 0.001); sTn expression was related to the first stages of the tumor invasion in transitional tissue. As regards ST6GalNAc I activity, we found an enhancement in transitional tissue. Statistical correlation analysis did not reveal association between sTn expression and ST6GalNAc I activity. CONCLUSIONS: Our findings indicated that sTn antigen tissue expression and ST6GalNAc I activity levels were not correlated in CRC, in spite of the overexpression of the antigen in tumorous and transitional tissue.
Assuntos
Adenocarcinoma/metabolismo , Antígenos Glicosídicos Associados a Tumores/metabolismo , Biomarcadores Tumorais/metabolismo , Neoplasias do Colo/metabolismo , Sialiltransferases/metabolismo , Adenocarcinoma/enzimologia , Adenocarcinoma/imunologia , Adenocarcinoma/patologia , Idoso , Antígenos Glicosídicos Associados a Tumores/análise , Neoplasias do Colo/enzimologia , Neoplasias do Colo/imunologia , Neoplasias do Colo/patologia , Feminino , Regulação Enzimológica da Expressão Gênica , Regulação Neoplásica da Expressão Gênica , Humanos , Imuno-Histoquímica , Masculino , Sialiltransferases/análise , Regulação para Cima , beta-D-Galactosídeo alfa 2-6-SialiltransferaseRESUMO
It has been reported that surface glycoconjugates in tumour cells have more complex and more heavily sialylated sugar chains in glycoproteins. Here, we analysed CMP-NeuAc:asialofetuin sialyltransferase activities in total cell membranes from colorectal cancer tissue with respect to normal adjacent tissue, finding enhanced sialyltransferase activities. Determination of the kinetic parameters for the donor substrate, CMP-NeuAc, revealed that the apparent K(m) in tumour tissue was decreased as regards to the normal value. Furthermore, we failed to find any correlation between this activity and the characteristics of the samples such as the age or sex of the patient, or Dukes' stage of the tumour. In order to know which sialyltransferase activity was altered, we studied the incorporation of NeuAc into N- and O-linked chains from asialofetuin. The results allow us to conclude that it is on N-linked chains where the activity is enhanced. With respect to alpha(2,3)- and alpha(2,6)-NeuAc linkages, we observed that enhanced activity in tumour tissues affects both linkages equally.