Differential display was used to define differences in gene expression between murine EMT-6 mammary carcinoma cells grown in monolayer or as spheroids in cell culture. Eighty different combinations of primer sets made of four anchored oligodeo(dT) primers (T(12)MG, T(12)MA, T(12)MT or T(12)MC) and twenty arbitrary ten base primers (AP1-20) were used for RT-PCR of total purified RNA from EMT-6 monolayers or spheroids. After re-screening, fourteen DNA fragments were identified as being selectively expressed in EMT-6 cells grown as spheroids. The fragments were cloned into the pCR II vector. Two of the fourteen cDNA fragments corresponded to mRNA selectively expressed in EMT-6 cells grown as spheroids. These clones were sequenced and found by database searching to correspond to murine heme oxygenase and murine beta(2)-microglobulin. There was a 5.3-fold higher expression of beta(2)-microglobulin and a 5.3-fold greater expression of heme oxygenase in EMT-6 cells grown as spheroids than in the same cells grown as monolayers. These studies reflect the phenotypic flexibility of cells depending upon the growth environment.

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