Identification of a novel tumor suppressor gene on chromosome arm 18q in human pancreatic caner

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Loss of 18q is highly frequent in human pancreatic cancer. A tumor suppressor gene, SMAD4, resides in this region, but introduction of this gene inhibit tumor cell growth only in vivo by means of angiogenesis inhibition through ETS. Introduction of chromosome 18, however, inhibit both in vitro and in vivo. Moreover, in most of the early lesions of the pancreatic tumorigeneses, 18q is lost but SMAD4 functions normally. Allelotype analyses on 18q identified a commonly lost region between D18S451 and D18S462. Database search indicated a total of 164 protein coding genes. One of such genes, PMAIP1, was picked up by the microarray analyses. This gene is frequently suppressed in pancreatic cancer. Upregulation of this gene caused suppression of the cell growth in pancreatic cancer cells. On the contrary, siRNA-mediated knockdown of the PMAIP1 stimulated cell growth. Thus, the PMAIP1 gene is one of the candidate tumor suppressor genes for pancreatic cancer.We further performed systematic knockdown studies using siRNAs for all the protein-coding genes in the commonly deleted region. Recovery of the cell growth was monitored and we picked up a total of 13 candidate genes. Further detailed studies are necessary.In the course of these studies, we developed a modified buffer system for ligation. Using this system, we can perform ligations in a cheap, efficient, and rapid manner. A total of 100 ligation reaction can be done within a 10 minutes only spending one dollar for 100 reactions. Thus, we named this method as "Coffee break ligation technique."