The basic and clinical implications of ABC transporters, Y-box-binding protein-1 (YB-1) and angiogenesis-related factors in human malignancies

In our laboratories, we have been studying molecular targets which might be advantageous for novel cancer therapeutics. In this review, we focus on how ATP-binding cassette (ABC) transporter superfamily genes, Y-box-binding protein-1 (YB-1), and tumor angiogenesis-associated factors could contribute to the development of novel strategies for molecular cancer therapeutics. ABC transporters such as P-glycoprotein/MDR1 and several MRP family proteins function to protect cells from xenobiotics, drugs and poisons, suggesting that ABC transporters are a double-edged sword. In this regard, P-glycoprotein/MDR1 is a representative ABC transporter which plays a critical role in the efflux of a wide range of drugs. We have reported that gene amplification, gene rearrangements, transcription factor YB-1 and CpG methylation on the promoter are involved in MDR1 gene overexpression in cultured cancer cells. Among them, two mechanisms appear to be relevant to the up-regulation of MDR1 gene in human malignancies. We first reported that MDR1 gene promoter is activated in response to environmental stimuli, and is modulated by methylation/demethylation of CpG sites on the MDR1 promoter. We also demonstrated that YB-1 modulates not only transcription of various genes associated with cell growth, drug resistance and DNA synthesis, but also translation, mRNA stabilization and DNA repair/self-defense processes. Angiogenesis is also involved in tumor growth, invasion and metastasis of various malignancies, and so angiogenesis-related molecules also offer novel molecular targets for anticancer therapeutics.