BACKGROUND: MicroRNAs (miRNAs), small RNA molecules of approximately 22 nucleotides, have been shown to be up-or downregulated in specific cell types and disease states. These molecules have become recognized as one of the major regulatory gatekeepers of coding genes in the human genome.CONTENT: We review the structure, nomenclature, mechanism of action, technologies used for miRNA detection, and associations of miRNAs with human cancer. miRNAs are produced in a tissue-specific manner, and changes in miRNA within a tissue type can be correlated with disease status. miRNAs appear to regulate mRNA translation and degradation via mechanisms that are dependent on the degree of complementarity between the miRNA and mRNA molecules. miRNAs can be detected via several methods, such as microarrays, bead-based arrays, and quantitative real-time PCR. The tissue concentrations of specific miRNAs have been associated with tumor invasiveness, metastatic potential, and other clinical characteristics for several types of cancers, including chronic lymphocytic leukemia, and breast, colorectal, hepatic, lung, pancreatic, and prostate cancers.

XPA is a protein essential for nucleotide excision repair (NER) where it is thought to function in damage recognition/verification. We have proposed an additional role, that of a processivity factor, conferring a processive mechanism of action on XPF and XPG, the endonucleases involved in NER. The present study was undertaken to examine the domain(s) in the XPA gene that are important for the ability of the XPA protein to function as a processivity factor. Using site-directed mutagenesis, mutations were created in several of the exons of XPA and mutant XPA proteins produced. The results showed that the DNA binding domain of XPA is critical for its ability to act as a processivity factor. Mutations in both the zinc finger motif and the large basic cleft in this domain eliminated the ability of XPA to confer a processive mechanism of action on the endonucleases involved in NER.Keywords xeroderma pigmentosum; XPA protein; DNA repair; processive mechanism of action Though the XPA protein is a key component in NER, its precise function in this repair pathway is not clear. There is evidence that it plays a role in the initial steps of NER, where it is involved in damage recognition/verification [1][2][3]. We have proposed an additional important function for XPA, that of a processivity factor needed to confer a processive mechanism of action on the endonucleases, XPF and XPG, involved in NER [4,5]. Proteins can locate target sites on DNA by two distinctive mechanisms: (1) a processive mechanism in which a protein first binds to a random site on DNA and then translocates to a specific site by a facilitated-diffusion process in which it slides or hops along the DNA; or (2) a distributive mechanism, in which a protein has no affinity for non-target DNA and locates target sites by a random, threedimensional diffusion process [6][7][8][9]. The mechanism utilized by DNA-targeting proteins is extremely important in determining the ability of the protein to properly interact with its target sites on DNA and, for many of these proteins, a processive mechanism of action is essential [6,8] We have previously shown that during repair of UVC light induced cyclobutane pyrimidine dimers in normal human cells, the endonucleases, XPG and XPF, incise DNA at sites of damage using a processive mechanism of action [4,5]. In contrast, these endonucleases in cells from

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Applications of molecular diagnostics to oncology have been slow to make their way to the clinical laboratory. While numerous genes and mutation spectra have been found to be involved in tumorigenesis, it is only recently that these findings begin to become useful in a clinical setting. Building on the technical knowledge obtained from molecular infectious disease testing, new instruments and assays have been developed to answer similar questions regarding qualitative, quantitative and genotyping issues. In this manuscript we describe two current examples of clinical molecular diagnostic applications, the assessment of BCR-ABL in chronic myelogenous leukemia patients and the detection of tumor cells in the sentinel lymph nodes of breast cancer patients, to demonstrate the role of molecular techniques in a routine clinical setting.

The application of genetic testing to predict how well or how poorly an individual will respond to a therapeutic drug is beginning to make its way into the clinical laboratory. As this testing begins to unfold in the clinical setting, there is a necessary paradigm change that must occur for the laboratory and for the healthcare provider in order for this to be successful. New molecular-based technologies are commercially available to perform this testing on a routine basis and several established examples of pharmacogenetic tests are currently being performed. Several national organizations are now working on practice guidelines for the incorporation of this testing into a clinical setting. This manuscript provides an overview of where we are with respect to pharmacogenetic testing.