IDENTIFICATION OF MESSENGER-RNAS DIFFERENTIALLY EXPRESSED IN QUIESCENCE OR IN LATE G1 PHASE OF THE CELL-CYCLE IN HUMAN BREAST-CANCER CELLS BY USING THE DIFFERENTIAL DISPLAY METHOD

Background: The decision for a cell to enter the DNA synthesis (S) pha se of the cell cycle or to arrest in quiescence is likely to be determ ined by genes expressed in the late G1 phase, at the restriction point . Loss of restriction point control is associated with malignant cellu lar transformation and cancer. For this reason, identifying genes that are differentially expressed in late G1 phase versus quiescence is im portant for understanding the molecular basis of normal and malignant growth. Materials and Methods: The differential display (DD) method de tects mRNA species that are different between sets of mammalian cells, allowing their recovery and cloning of the corresponding cDNAs. Using this technique, we compared mRNAs from synchronized human breast canc er cells (21PT) in quiescence and in late G1. Results: Six mRNAs diffe rentially expressed in lace G1 or in quiescence were identified. One m RNA expressed 10 hr after serum induction showed 99% homology to a pep tide transporter involved in antigen presentation of the class I major histocompatibility complex (TAP-1) mRNA. Another mRNA expressed speci fically in quiescence and down-regulated 2 hr following serum inductio n showed 98% homology to human NADP(+)-dependent cytoplasmic malic enz yme (EC1.1.1.40) mRNA, which is an important enzyme in fatty add synth esis and lipogenesis. Three others showed high homology to different m RNAs in the GeneBank, corresponding to genes having unknown functions. Finally, one mRNA revealed no significant homology to known genes in the GeneBank. Conclusions: We conclude that DD is an efficient and pow erful method for the identification of growth-related genes which may have a role in cancer development.