Expression of the protooncogene
c-Myb protein was assessed in normal mucosa and in
tumor samples resected from six patients. We found that the
tumor samples always expressed higher levels of full length Myb
protein than the normal tissue. This contrasts with the situation in c-myb-associated hemopoietic
malignancies of the mouse and chicken, in which Myb
proteins are generally amino or carboxyl truncated. Tissues from five patients with colonic
adenomatous polyps were also examined and found to express levels of Myb that were, in general, intermediate between those found in normal tissues and
tumors. Of particular interest is that the more dysplastic
polyps displayed higher Myb levels. In one patient with
carcinoma and multiple
colonic polyps, some
polyps had intermediate levels of Myb, whereas one
polyp with
carcinoma in situ expressed
tumor-like levels of Myb. To directly test the hypothesis that Myb expression may be important in determining the rate of colonic cell proliferation, we examined three colonic
carcinoma cell lines and one
polyp cell line. We found that the cell lines with the most rapid doubling times exhibited the highest Myb levels. In addition, we show that antisense myb
oligonucleotides retard the proliferation of one of these colonic cell lines which expresses the highest level of Myb.