Analysis of KRAP expression and localization, and genes regulated by KRAP in a human colon cancer cell line.

We previously identified the human KRAP (Ki-ras-induced actin-interacting protein) gene from the cDNA library of human colon cancer HCT116 cells as one of the genes whose expression levels were up-regulated by activated Ki-ras. Although the KRAP gene is structurally conserved from fish to mammalian species, the expression pattern and function of KRAP still remain to be elucidated. Here, we have generated a specific polyclonal antibody for KRAP and characterized the histological expression of KRAP in mouse tissues. KRAP was ubiquitously expressed in mouse tissues, with high levels in pancreas, liver, and brown adipose tissues, and KRAP was co-localized with filamentous actin along the apical membranes in both pancreas and liver tissues. A subfractionation study revealed that KRAP is a cytoplasmic protein and that the majority is associated with the cytoskeleton. Furthermore, microarray gene expression profile by inhibiting KRAP expression in HCT116 cells showed that several receptors and signal molecules frequently deregulated in cancers were differentially expressed in the KRAP-knockdown cells. All of these results suggested that KRAP might be a cytoskeleton-associated protein involving the structural integrity and/or signal transductions in human cancers.