The Journal of biological chemistry
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DNA damaging agents induce a conserved intra-S-phase checkpoint that inhibits DNA replication in eukaryotic cells. To better understand this checkpoint and its role in determining the efficacy of antitumor drugs that damage DNA, we examined the effects of adozelesin, a DNA-alkylating antitumor agent that has a profound inhibitory effect on initiation of DNA replication in mammals, on the replication of Saccharomyces cerevisiae chromosomes. Adozelesin inhibited initiation of S. cerevisiae DNA replication by inducing an intra-S-phase DNA damage checkpoint. ⋯ Defects in both initiation and checkpoint regulation in the orc2-1 strain were suppressed by deletion of a gene encoding a putative acetyltransferase, SAS2. Adozelesin also induced a cellular response that requires a function of ORC in G(1). A similar G(1)-specific response in mammals may contribute to the cytotoxic and antitumor properties of this and other DNA-damaging drugs.
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Prolactin-dependent signaling occurs as the result of ligand-induced dimerization of the prolactin receptor (PRLr). While three PRLr isoforms have been characterized in the rat, studies have suggested the existence of several human isoforms in breast carcinoma species and normal tissues. Reverse transcription polymerase chain reaction was performed on mRNA isolated from the breast carcinoma cell line T47D, revealing two predominant receptor isoforms: the previously described long PRLr and a novel human intermediate PRLr. ⋯ In contrast, the intermediate PRLr transfectants showed equivalent levels of Jak2 activation but only minimal activation of Fyn. Last, Northern analysis revealed variable tissue expression of intermediate PRLr transcript that differed from that of the long PRLr. Taken together, differences in signaling and tissue expression suggest that the human intermediate PRLr differs from the long PRLr in physiological function.