Molecular Pathology: Future Issues

Archives of Pathology & Laboratory Medicine,  May 2006  by Kiechle, Frederick L,  Zhang, Xinbo,  Holland, Carol

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Context.-The field of molecular pathology is expanding in complexity. To achieve competency, vigilance is required.

Objective.-To review the advances in clinically useful molecular biologic techniques and to identify their applications in clinical practice, as presented at the 13th Annual William Beaumont Hospital DNA Symposium.

Data Sources.-The 4 manuscripts submitted were reviewed and their major findings were compared with the literature on the same or related topics.

Study Selection.-Manuscripts address the use of molecular or immunophenotyping by flow cytometry to evaluate the origin or presence of sepsis, respectively; the use of imatinib mesylate to treat chronic myeloid leukemia and the nature of resistance to imatinib; and the use of 9 and 10 fluorochromes during clinical flow cytometric studies.

Data Synthesis.-The epidemiologic evaluation of a septic outbreak may be monitored using molecular techniques that track the relatedness of isolates. A potential biomarker for the presence of early sepsis is CD64. Intracellular signal transduction pathways are altered in malignancy. Imatinib mesylate inhibits the BCR-ABL kinase created by translocation of the long arms of chromosomes 9 and 22 in chronic myeloid leukemia. Resistance to imatinib may be secondary to mutation in the BCR-ABL kinase domain or residual leukemic stem cells that imatinib does not kill. The use of 9 or 10 fluorochromes simultaneously during flow cytometry has many clinical advantages; however, software for data analysis is needed.

Conclusion.-The current postgenomic era will continue to emphasize the use of microarrays and database software for genomic, transcriptomic, proteomic, nutrigenomic, and pharmacogenomics screening to search for a useful clinical assay. The number of molecular pathologic techniques will expand as additional disease-associated mutations are defined.

(Arch Pathol Lab Med. 2006;130:650-653)

This issue of the Archives of Pathology & Laboratory Medicine features 4 articles presented at the 13th Annual William Beaumont Hospital DNA Symposium, titled "DNA Technology in the Clinical Laboratory," held October 7 through 9, 2004, in Troy, Mich. "The history of molecular biology provides a model for understanding how original research takes shape, independent of potential applications."1 Today, the applications are emerging in genomics (DNA sequence), transcriptomics (critical messenger RNA identification), proteomics (protein identification), and pharmacogenomics (genes that define drug behavior). The quality of the current human genome sequence has been assessed.2,3 The error rate is approximately 1 event per 100 000 bases in 2.85 billion nucleotides interrupted by 341 gaps.3 The gaps are usually associated with segmentai duplications3 that require the combination of a whole-genome shotgun sequence assembly coupled with a targeted clone-by-clone approach to resolve the duplications.4 It is estimated that the human genome encodes 20 000 to 25 000 protein-coding genes.4

In the postgenomic era, there is an important trend toward the selection of diet or pharmaceutical agents based on an individual's genetic make-up (nutrigenetics or pharmacogenetics) or the use of genomic tools to define how diet or drugs alter metabolic pathways and homeostatic control (nutrigenomics or pharmacogenomics).5,6 These approaches are referred to as personalized nutrition and medicine and should provide more effective therapy with less hit and miss trials of diets or drugs that are ineffective for a specific individual genotype.

The next section explores the role of fatty acid synthase (FAS) in normal and cancerous cells. One should note that there is nutritional and hormonal regulation of FAS in normal liver and adipose cells that is absent in the upregulated FAS in many cancer cells. This illustration emphasizes the importance of understanding the differences in intracellular signal transduction in benign and malignant cells and the potential of FAS as a pharmaceutical target for inhibition of enzyme activity and induction of apoptosis.

FAS: SIGNAL TRANSDUCTION EXAMPLE

Fatty acid synthase is a 250- to 270-kd protein complex that is a homodimer and contains 7 enzymes: ketoacyl synthase, acetyl transacylase, malonyl transacylase, hydratase enoyl reductase, ketoacyl reductase, acyl carrier protein, and thioesterase.7 Based on the intracellular location of FAS, there are 2 kinds of FAS proteins: cytosolic and mitochondrial FASs. Cytosolic FAS is responsible for de novo fatty acid synthesis, and mitochondrial FAS exclusively transfers malonyl moieties to the mitochondrial holo-acyl carrier proteins. Mitochondrial FAS may also play an important role in mitochondrial function, particularly as it relates to apoptosis.8 Because diet supplies most fatty acids, the requirement of endogenous synthesis is minimal in normal cells. Consequently, FAS is expressed at low to undetectable levels in most normal human tissues. In contrast, FAS is overexpressed in a large number of human cancers despite high levels of ambient fatty acids. Interestingly, inhibitors of FAS induce apoptosis in cultured human breast cancer cells9 and have shown significant antitumor activity against human breast9 and other tumors.