Deregulated expression of KRAP, a novel gene encoding actin-interacting protein, in human colon cancer cells

Abstract

We have identified a novel gene, designated KRAP (Ki-ras-induced actin-interacting protein), encoding a protein of 1,259 amino acids with coiled-coil regions and transmembrane regions, from the cDNA library of human colon cancer HCT116 cells, as one of the genes upregulated by activated Ki-ras. While KRAP was rarely expressed in normal colon epithelium, deregulated constitutive KRAP expression was observed in some other colon cancer cells. In normal tissues, KRAP was strongly expressed in pancreas and testis. Anti-KRAP polyclonal antibodies detected endogenous KRAP as the molecular size of M r 180,000, and immunofluorescence microscopy and cytochalasin E treatment revealed that KRAP was clearly associated with the actin filaments. Furthermore, KRAP was localized as a membrane-bound form with extracellular regions. These results together suggested KRAP might be involved in the regulation of filamentous actin and signals from the outside of the cells.

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

“…F-actin was visualized with rhodaminephalloidin (molecular probe) according to the manufacturer's protocol. Fluorescence images were acquired by confocal fluorescence microscopy, as described previously (Inokuchi et al 2004). …”

“…The human KRAP (Ki-ras-induced actin-interacting protein) gene was originally identified as one of the genes whose expression levels were up-regulated by activated Ki-ras in human colon cancer HCT116 cells (Inokuchi et al 2004). While KRAP was rarely expressed in normal colon epithelium, deregulated constitutive KRAP expression was observed in some cancer cells (Inokuchi et al 2004).…”

“…While KRAP was rarely expressed in normal colon epithelium, deregulated constitutive KRAP expression was observed in some cancer cells (Inokuchi et al 2004). In humans, KRAP mRNA was most strongly expressed in the pancreas and testis, with ubiquitous distribution among the other organs at the lower levels (Inokuchi et al 2004).…”

“…While KRAP was rarely expressed in normal colon epithelium, deregulated constitutive KRAP expression was observed in some cancer cells (Inokuchi et al 2004). In humans, KRAP mRNA was most strongly expressed in the pancreas and testis, with ubiquitous distribution among the other organs at the lower levels (Inokuchi et al 2004). KRAP is structurally predicted to possess a coiled-coil motif within its C terminus and exogenous KRAP expression was localized along the actin stress fibers in NIH3T3 cells (Inokuchi et al 2004), suggesting that the KRAP might be involved in the regulation of F-actin.…”

“…In humans, KRAP mRNA was most strongly expressed in the pancreas and testis, with ubiquitous distribution among the other organs at the lower levels (Inokuchi et al 2004). KRAP is structurally predicted to possess a coiled-coil motif within its C terminus and exogenous KRAP expression was localized along the actin stress fibers in NIH3T3 cells (Inokuchi et al 2004), suggesting that the KRAP might be involved in the regulation of F-actin. KRAP is structurally well conserved from fish to mammalian species (UCSC Genome Browser) and mouse KRAP has high amino acid sequence identity with human KRAP, together suggesting that KRAP may play physiologically critical roles.…”