CaSm: an Sm-like protein that contributes to the transformed state in cancer cells.

A novel gene encoding a protein containing Sm motif-like domains was found to have elevated expression in pancreatic cancer and in several cancer-derived cell lines. CaSm (for Cancer-associated Sm-like) mRNA is up-regulated in 87.5% (seven of eight) of pancreatic tumor/normal pairs. Similarly, cell lines from cancers originating in liver, ovary, lung, and kidney show increased CaSm expression compared to their normal tissue cognates. CaSm encodes a 133-amino acid open reading frame that contains the two Sm motifs found in the common snRNP proteins, with the greatest homology to the Sm G protein (60% similarity). Two hypothetical proteins from Caenorhabditis elegans and Saccharomyces cerevisiae share even greater similarity (72.8 and 67.7%, respectively), suggesting a broad family of proteins containing Sm motifs. Antisense CaSm RNA is able to alter the transformed phenotype of pancreatic cancer cells by reducing their ability to form large colonies in soft agar when compared to untransfected cells. Therefore, CaSm expression appears to be necessary for maintenance of the transformed state.