Increased expression after X-irradiation of MUC1 in cultured human colon carcinoma HT-29 cells.

The effect of X-irradiation on production of MUC1 was studied with human colon carcinoma HT-29 cells. As evaluated by immunocytochemical staining, the percentages of MUC1-positive cells in cells at 4 days after 6 Gy irradiation and in unirradiated control cells were 52 +/- 3.5% (n = 6) and 26 +/- 2.8% (n = 6), respectively. Flow-cytometric analysis of living cells showed that MUC1 began to rise from day 1, reaching a plateau by day 4 after 6 Gy irradiation. Western blot analysis with monoclonal antibody MY.1E12 against glycosylated MUC1 (mature form) showed dose-dependent increases of two bands (500 and 390 kDa) corresponding to two polymorphic MUC1 alleles. Premature forms of MUC1 (350 and 240 kDa) were detectable with monoclonal antibody HMFG-2 only in irradiated cells, suggesting that new core protein synthesis had been induced. The transcriptional activity of the MUC1 gene was analyzed in terms of transient expression of MUC1-CAT reporter plasmids containing 5'-flanking sequences of the MUC1 gene fused to the bacterial chloramphenicol acetyltransferase (CAT) gene. The results of CAT assay indicate that enhanced expression of MUC1 in irradiated HT-29 cells was due to upregulation of MUC1 transcription, and required the upstream promoter.