Preparation of cDNA libraries from vascular cells.

The vast majority of past and present efforts in the molecular cloning of expressed sequences involve isolation of clones from cDNA libraries constructed in bacteriophage lambda (1,2). As discussed in Chapter 6 , screening these cDNA libraries using labeled probes remains the most straightforward method to isolate full length cDNAs for which some partial sequence information is known. Although the availability of high quality reagents and kits over the past decade has made the process of library construction increasingly straightforward, generation of high-quality libraries is a task that still requires a fair amount of dedicated effort. Because alternative PCR-based cloning strategies have become increasingly popular alternatives to cDNA library screening, it is useful to consider the advantages and disadvantages of each strategy before embarking on a project to construct a cDNA library (Table 1). In our opinion, it is worthwhile to construct a cDNA library when the transcript of interest is not exceedingly rare (i.e., can readily be detected by Northern blot analysis of total RNA), when multiple cDNAs will need to be cloned over a period of time, and in situations where occasional mutations can not be tolerated (for example, if the cDNA is to be expressed in mammalian cells to examine function). In situations where the transcript of interest is expressed at exceedingly low levels, or when only a single cDNA needs to be cloned, a PCR-based strategy should be considered. When the tissue source is precious (such as a unique clinical specimen), successful construction of a phage library provides a resource that can be amplified and used for multiple cloning projects over many years, but runs the risk of consuming the available RNA if the library construction fails. Table 1 Comparison of Relative Advantages of cDNA Cloning from Lambda Phage Libraries by Plaque Hybridization Compared to Newer PCR- Based Strategies Lambda phage cDNA library PCR-based strategy Freedom from error ++ +/- Able to detect very rare transcripts - ++ Reusable ++ - Useful for rare/precious tissue samples - ++

Domino reactions for library synthesis of small molecules in combinatorial chemistry.

Domino reactions are highly efficient processes that allow the synthesis of complex molecules starting from simple substrates, in a straightforward fashion. The transformations are extremely useful for the design of small-molecule libraries by combinatorial chemistry if multicomponent domino reactions are employed. The reactions can be performed in solution, as well as on solid support, and give access to highly diverse molecules; in addition, their use in automated synthesis is possible.

SM-20 is a novel 40-kd protein whose expression in the arterial wall is restricted to smooth muscle.

We have previously reported the identification of a novel cDNA, SM-20, whose corresponding mRNA levels are regulated by growth factors in rat aortic smooth muscle cell (SMC) culture. Affinity-purified polyclonal and monoclonal antibodies were made against a 230 amino acid region of the SM-20 putative peptide expressed in the bacterial vector, pET-3b. Western blot analyses of rat and human SMC lysates detected a single protein species of approximately 40 kd. SM-20 was not detected in concentrates of the culture medium. By immunohistochemistry, SM-20 was localized to filaments in the cytoplasm of cultured SMC. Like SM-20 mRNA, levels of SM-20 protein were increased 1-3 hours after serum stimulation of rat aortic SMC. In rat tissues, SM-20 antigen was detected in abundance in smooth, cardiac, and skeletal muscle. SM-20 was also detected in some epithelial cells of the kidney, pancreas, gastrointestinal tract, and skin, but was not found in the parenchyma of the liver, spleen, or testis. In the rat arterial wall, SM-20 antigen was restricted to the SMC of the media and, after balloon arterial injury, was found most abundantly in the neointima. In human atherosclerotic coronary arteries, SM-20 antigen predominated in the SMC of the intimal plaques and was not detected in macrophages, endothelium, or adventitial cells. Thus, SM-20 encodes a protein which serves as a novel SMC-specific marker within the vessel wall.

Identification of lysyl oxidase and other platelet-derived growth factor-inducible genes in vascular smooth muscle cells by differential screening.

BACKGROUND: Atherosclerosis and arterial injury are characterized by vascular smooth muscle cell (VSMC) migration and growth and an increase in synthesis of extracellular matrix. Platelet-derived growth factor (PDGF) has been implicated in these processes. This study was designed to identify additional PDGF-regulated genes in VSMC. EXPERIMENTAL DESIGN: A cDNA library prepared from PDGF-stimulated rat aortic VSMC was screened by differential hybridization to identify clones representing PDGF-inducible genes. The time course of growth factor-induced changes in gene expression was examined by RNA blot hybridization. Assays of protein activity were also performed for selected gene products. RESULTS: Four PDGF-regulated cDNA clones were identified by DNA sequencing. These encoded the extracellular matrix proteins lysyl oxidase (LO), thrombospondin, and osteopontin and the intracellular enzyme lactate dehydrogenase (LDH). Levels of mRNA corresponding to all four genes were low in quiescent VSMC and were markedly induced by PDGF, angiotensin II, and 10% calf serum. The regulation of LO and LDH mRNA by these agonists in VSMC has not been previously reported. LO enzymatic activity in the culture media was increased by approximately equals to 700% after exposure to PDGF. In contrast, LDH activity was not increased by PDGF treatment. CONCLUSIONS: The induction of LO mRNA and its secretion by VSMC is an early event accompanying growth factor stimulation and may contribute to organization of the extracellular matrix.