Mechanism of cAMP-growth regulatory function

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Our long term goal is to elucidate the principles by which cAMP controls cell development, proliferation and diffrentiation. cAMP regulates a striking number of physiologic processes, including intermediary metabolism, cellular proliferation, and neuronal signaling by altering basic pattrens of gene expression via activation of cAMP response element (CRE)-directed transcription. The mechanism of the CRE-directed transcription in cell proliferation, however, is largely unexplored. To elucidate the role of the cAMP enhancer (CRE) in the control of cell proliferation, we used transcription factor-decoy oligonucleotide approach. Our studies revealed that a synthetic single-stranded oligonucleotide composed of the CRE sequence, which self-hybridizes to form a duplex/hairpin, can penetrate into cells, compete with CRE enhancers for binding transcription factors and specifically interfere with CRE- and Ap-1-directed transcription in vivo . This oligonucleotide restrained tumor cell proliferation, without affecting the growth of non-cancerous cells. These results suggest that the role of PKA in cancergenesis may involve its transcription of array of genes. Recent development of high throughput DNA microarray enables parallel analysis of expression profiles of thousands of genes in a single hybridization for complex biological systems. Using DNA microarrays, we have conducted a systematic charaterization of gene expression in cells exposed to antisense, either exogenously or endogenously. We have found that in a sequence-specific manner, antisense targeted to protein kinase A RIa alters expression of the clusters of coordinately expressed genes at a specific stage of cell growth, differentiation, and activation. The genes that define the proliferation-transformation signature are down-regulated, whereas those that define the differentiation-reverse transformation signature are up-regulated in antisense-treated cancer cells and tumors, but not in host-livers. In this differentiation signature, the genes showing the highest induction include genes for the G proteins Rap1 and Cdc42. The expression signature induced by the exogenously supplied antisense oligodeoxynucleotide overlaps strikingly with that induced by endogenous antisense gene overexpression. The microarray analysis of gene profiling is also underway in cells treated with CRE-decoy oligonucleotides. This approach will lead us to potentially survey all the genetic pathways and also to discover hitherto unrecognized novel genes that may be involved in tumor growth and tumorigenesis. Furthermore, the discovery of novel genes by this approach coupled with the genetic and biochemical analyses may unravel the mechanism of cAMP-deregulation underlying cancergenesis and offer new targets for drug development and novel treatment strategies for cancer.