Oncogene and receptor expression

c-myc mRNA expression in non-Hodgkin's lymphomas

Steady state c-myc mRNA levels determined by Northern blot analysis were examined in non-Hodgkin's lymphomas (NHL) of both high (n = 29) and low malignancy (n = 18), and in non-specific chronic lymphadenitis (n = 6). High grade NHL, classified according to the updated Kiel classification, revealed significantly larger amounts of c-myc mRNA compared with low grade NHL and lymphadenitis. mRNA levels in non-specific lymphadenitis were lower than in low grade NHL, but the differences were not statistically significant. No correlation between c-myc mRNA levels and the immunologic phenotype was discernible. Growth fractions of the NHL were determined by immunostaining with the monoclonal antibody Ki-67. Significant correlations between the percentages of Ki-67-positive cells, as well as the amounts of c-myc mRNA, and classification into high or low grade NHL were found. However, the percentage of Ki-67 positive cells and c-myc mRNA levels in individual cases and in the various histologic entities of NHL did not correlate. Our results indicate the overexpression of the c-myc gene in NHL, and a highly significant correlation of steady state c-myc mRNA levels with the prognosis-related histomorphologic Kiel classification of NHL into different subgroups of low and high grade malignancy.

Regulation of surface-differentiation molecules by epidermal growth factor, transforming growth factor alpha, and hydrocortisone in human mammary epithelial cells transformed by an activated c-Ha-ras proto-oncogene

Spontaneously immortalized human mammary epithelial cells MCF-10A were transfected with an activated c-Ha-ras oncogene. Transfected cells (MCF-10T) acquire a malignant phenotype, as already reported. Studies of 125I-2'-deoxyuridine incorporation in cultures given graded doses of hydrocortisone (HC), cholera toxin (CT), epidermal growth factor (EGF), and transforming growth factor alpha (TGF-alpha) showed that though MCF-10T had become almost independent on exogenous EGF and TGF-alpha, they continued to respond to the synergistic effect of HC and CT plus EGF. Both lines were phenotypically characterized with an immunoradiometric assay in live cells. Expression of MHC class-I molecules, human milk-fat-globule-I antigen, and EGF receptor was reduced in ras-transfected cells, although other differentiation markers were unchanged. Exogenous EGF down-regulated the expression of functional EGF-R, selectively in transformed cells. TGF-alpha failed to modulate EGF-R. In contrast, HC strongly stimulated the expression of EGF-R while depressing MHC class-I molecules. Thus, it appears that in vivo HC may co-operate with TGF-alpha and EGF in promoting the growth of transformed mammary cells. This hormone might also favor the escape from immune surveillance by reducing the expression of surface differentiation markers.