We have devised a simple and efficient cDNA cloning strategy that overcomes many of the difficulties encountered in obtaining full-length cDNA clones of lowabundance mRNAs. In essence, cDNAs are generated by using the DNA polymerase chain reaction technique to amplify copies of the region between a single point in the transcript and the 3' or 5' end. The minimum information required for this amplification is a single short stretch of sequence within the mRNA to be cloned. Since the cDNAs can be produced in one day, examined by Southern blotting the next, and readily cloned, large numbers of full-length cDNA clones of rare transcripts can be rapidly produced. Moreover, separation of amplified cDNAs by gel electrophoresis allows precise selection by size prior to cloning and thus facilitates the isolation of cDNAs representing variant mRNAs, such as those produced by alternative splicing or by the use of alternative promoters. The efficacy of this method was demonstrated by isolating cDNA clones of mRNA from int-2, a mouse gene that expresses four different transcripts at low abundance, the longest of which is =2.9 kilobases. After <0.05% of the cDNAs produced had been screened, 29 independent int-2 clones were isolated. Sequence analysis demonstrated that the 3' and 5' ends of all four int-2 mRNAs were accurately represented by these clones.Despite the development of numerous cDNA cloning strategies (1-5), obtaining full-length cDNA copies of lowabundance mRNAs remains a formidable task. We describe here a simple, rapid, and efficient cDNA cloning strategy that is based on the DNA polymerase chain reaction (PCR) technique developed by Saiki et al. (6). PCR employs two oligonucleotide primers, one complementary to a sequence on the (+) strand and the other to a downstream sequence on the (-) strand. Reiterative cycles of denaturation, annealing, and extension are used to generate multiple copies of the DNA that lies between the two primers. PCR has been used for a variety of purposes (7-13), including the detection of allelic polymorphisms and of DNA sequences unique to rare cells in a population, as well as the cross-species isolation of homologous genes. The feature common to all applications of PCR to date has been the use of primers designed to match two known or presumed genomic or cDNA sequences. In contrast, we have devised an application of this technique that achieves amplification and cloning of the region between a single short sequence in a cDNA molecule and its unknown 3' or 5' end. We demonstrate here the utility of this strategy, termed "rapid amplification of cDNA ends" (RACE), by using it to obtain clones representing transcripts of a gene, int-2, expressed at low abundance in the early mouse embryo. METHODS 3'-End Amplification of cDNAs. See Fig. 1 and the substitution of 20 pmol of 5RT primer for (dT)17-adaptor. Excess 5RT was removed as follows: the 20-Al cDNA pool was applied to a Bio-Gel A-5m (Bio-Rad) column (in a 2-ml serological pipette plugged with silane-treated glass wool) equi...

In breast cancer, overexpression of ErbB2 or aberrant regulation of survivin, a member of the inhibitor of apoptosis family, is associated with resistance to chemo/hormone therapy and predicts for a poor clinical outcome. A functional link between the two predictive factors has not been previously shown. Here, using genetic and pharmacologic approaches to block ErbB2 signaling, we show that ErbB2 regulates survivin protein expression in ErbB2-overexpressing breast cancer cells. Selective knockdown of ErbB2 using small interfering RNA markedly reduced survivin protein, resulting in apoptosis of ErbB2-overexpressing breast cancer cell lines such as BT474. Alternatively, inhibition of ErbB2 signaling using lapatinib (GW572016), a reversible small-molecule inhibitor of ErbB1/ErbB2 tyrosine kinases, at pharmacologically relevant concentrations, leads to marked inhibition of survivin protein with subsequent apoptosis. The effect of lapatinib on survivin seems to be predominantly posttranslational, mediated by ubiquitin-proteosome degradation as lactacystin, a proteosome inhibitor, reverses these effects. Furthermore, lapatinib down-regulated the expression of Histagged survivin, which was under the transcriptional control of a heterologous promoter, providing additional evidence supporting a posttranslational mechanism of regulation. In contrast, trastuzumab and gefitinib failed to down-regulate survivin in ErbB2-overexpressing breast cancer cells. Importantly, the clinical relevance of these findings was illustrated in patients with ErbB2-overexpressing breast cancer whose clinical response to lapatinib was associated with marked inhibition of survivin in their tumors. These findings shed new light on the mechanism by which ErbB2 overexpression protects against apoptotic stimuli in breast cancer and identifies therapeutic interventions to improve clinical outcomes in these aggressive tumors. (Cancer Res 2006; 66(3): 1640-7)

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We have determined the nucleotide sequence of a functional mouse adenine phosphoribosyltransferase (APRT) gene and its cDNA. The amino acid sequence of the enzyme is deduced from an open reading frame in the cDNA and predicts a protein with a molecular weight of 19,560. The protein coding region of the gene is -2 kilobases, and it is composed of five exons and four introns. While the body of the gene is 53% G+C, the 200 nucleotides upstream from the ATG translation start codon are 66% G+C and contain three copies of the sequence C-C-G-C-C-C. The mouse APRT enzyme shares a homologous 20-amino acid sequence with mouse, hamster, and human hypoxanthine phosphoribosyltransferases (HPRTs) and several bacterial phosphoribosyltransferases. This sequence has previously been shown to be a likely catalytic domain in human HPRT and Escherichia coli glutamine phosphoribosyltransferase. Because of the similarities in function of these proteins, both eukaryotic and prokaryotic, it is not unexpected that they should exhibit one or more regions of homology, particularly at the 5-phosphoribosyl-1-pyrophosphate and purine binding sites, especially if they are related via a common evolutionary lineage. This homologous sequence is interrupted by a single intron in the mouse APRT gene and by two introns in the mouse HPRT gene. Furthermore, the positions of both introns in the HPRT sequence are different from that of the single intron in the corresponding sequence of the APRT gene.The gene encoding adenine phosphoribosyltransferase (APRT) has attracted considerable interest because of its utility as a selectable marker (1, 2). The enzyme, which is a member of a family of phosphoribosyltransferases, constitutes a purine salvage pathway that utilizes adenine and 5-phosphoribosyl-1-pyrophosphate (PRPP) to form AMP. Whether or not the enzyme is expressed provides the basis for sensitive forward and backward selection systems that permit selection of Aprt-or Aprt' cells, respectively (1, 2). The APRT enzyme has been purified from several mammalian species (3-5) and is a homodimer (3, 5). However, its amino acid sequence has not been determined, and only the amino acid composition of human APRT has been reported (3). Since the amino acid sequences of several eukaryotic and prokaryotic enzymes that bind PRPP and have phosphoribosyltransferase activity are known, it would be instructive to have available a mammalian APRT sequence for comparative purposes. We have previously described the cloning of mouse (6) and human (7) APRT genes, and in this report we present the nucleotide sequence of a functional mouse APRT gene and the deduced amino acid sequence of the protein.We also describe a highly conserved (or possibly convergent) nucleotide sequence and its encoded amino acid sequence that is shared by prokaryotic and eukaryotic phosphoribosyltransferases. These include the products of Escherichia coli gpt (xanthine guanine phosphoribosyltransferase) (8, 9), E. coli pur F (glutamine phosphoribosylpyrophosphate amidotransferase) (10), Ba...

The functional human adenine phosphoribosyltransferase (APRI) gene is <2.6 kilobases in length and contains five exons. The amino acid sequences of APRTs have been highly conserved throughout evolution. The human enzyme is 82%, 90%, and 40% identical to the mouse, hamster, and Escherichia coli enzymes, respectively. The promoter region of the human APRT gene, like that of several other "housekeeping" genes, lacks "TATA" and "CCAAT" boxes but contains five GC boxes that are potential binding sites for the Spl transcription factor. The distal three, however, are dispensable for gene expression. Comparison between human and mouse APRT gene nucleotide sequences reveals a high degree of homology within protein coding regions but an absence of significant homology in 5' flanking, 3' untranslated, and intron sequences, except for similarly positioned GC boxes in the promoter region and a 26-base-pair region in intron 3. This 26-base-pair sequence is 92% identical with a similarly positioned sequence in the mouse gene and is also found in intron 3 of the hamster gene, suggesting that its retention may be a consequence of stringent selection. The positions of all introns have been precisely retained in the human and both rodent genes, as has an unusual AG/GC donor splice site in intron 2. Particularly striking is the distribution of CpG dinucleotides within human and rodent APRT genes. Although the nucleotide sequences of intron 1 and the 5' flanking regions of human and mouse APRT genes have no substantial homology, they have a frequency of CpG dinucleotides that is much higher than expected and nonrandom considering the G+C content of the gene. Retention of an elevated CpG dinucleotide content, despite loss of sequence homology, suggests that there may be selection for CpG dinucleotides in these regions and that their maintenance may be important for APRT gene function.Adenine phosphoribosyltransferase (APRT, EC 2.4.2.7) catalyzes the formation ofAMP and inorganic pyrophosphate from adenine and 5-phosphoribosyl-1-pyrophosphate (PRPP). Its importance in metabolism probably relates to the production of adenine as a by-product of the ubiquitously distributed polyamine biosynthesis pathway (1). Deficiency of APRT activity is inherited as an autosomal recessive condition characterized by high urinary levels of adenine and 2,8-dihydroxyadenine (DHA), which may lead to a clinically significant DHA urolithiasis appearing during childhood or at a later age (2). The gene for human APRT has been mapped to chromosome 16 (3) at 16q24 (4). We have described the cloning of this gene and a relatively frequent Taq I restriction fragment length polymorphism within its largest intron (5).The APRT gene is constitutively expressed in all adult tissues with only moderate variation between different cell types (6). APRT activity increases about 2-fold during S phase of the cell cycle (7), probably reflecting a doubling of the number of gene copies. As is the case for some other "housekeeping" genes (8), the transcription promoter of ...