Co-overexpression of DEAD box protein rck/p54 and c-myc protein in human colorectal adenomas and the relevance of their expression in cultured cell lines

Abstract

The RCK gene was cloned through a study of the breakpoint of the t(11;14)(q23;q32) chromosomal translocation observed in a human B-cell lymphoma and overexpression of the protein (rck/p54) due to the translocation was shown to be associated with malignant transformation. The rck/p54 protein belongs to the DEAD box protein/RNA helicase family, which has a variety of functions such as translation initiation, pre-mRNA splicing and ribosome assembly. It is considered that rck/p54 protein may have significant effects on the mRNA structure of genes associated with cell proliferation, facilitating protein synthesis. Expression of rck/p54 in colorectal adenomas, which are a premalignant lesion of colorectal cancer, was examined by Western blot analysis and immunohistochemistry. The rck/p54 protein was found to be overexpressed in tumor tissues resected from 17 of 26 cases (65.4%) of colorectal adenomas and 13 of 14 c-myc-positive cases (92.8%) also co-overexpressed rck/p54 protein. Thus, a significant correlation between rck/p54 and c-myc co-overexpression was found (Spearman's rank correlation, P = 0.0018). We demonstrate that overexpression of rck/p54 in two different cell lines, COS 7 and human colorectal cancer cell line SW480, caused an increase in c-myc protein levels by enhancement of its translation efficiency and/or stabilization of its mRNA. These results suggest that rck/p54 of the DEAD box protein/RNA helicase family may contribute to cell proliferation and carcinogenesis in the development of human colorectal tumors at the translational level by increasing synthesis of c-myc protein.

Human DEAD-box/RNA unwindase rck/p54 contributes to maintenance of cell growth by affecting cell cycle in cultured cells

“…The level of T-RCK, which represents the total mRNA levels of RCK, also paralleled those of the protein expression; however, the increase in the ratio of TSS1 (transcripts from exon 1a) to T-RCK was greater than that in the ratio of TSS2 (transcripts from exon 1b) to T-RCK. The levels of c-myc mRNA and protein, which we previously reported to be high when rck/p54 expression was high (19), were similar to those of rck/p54 and T-RCK. We also monitored the levels of p-Erk and p-Akt as markers for cell proliferation and survival.…”

“…Our study on crystallization of rck/p54 protein (33) and surface plasmon resonance assay indicated that rck/p54 has very high affinity for RNAs. Moreover, we previously reported that rck/p54 stabilized c-myc mRNAs and increased the translation-initiation efficiency in colon cancer SW480 cells (19). Collectively, the data suggest that rck/p54 probably promotes cell growth-related gene expression at translationinitiation machinery by cooperating with eIF4E or eIF4E-complex proteins in cancer cells.…”

“…So far, we have consistently reported data showing that high expression of rck/p54, a human DEAD-box/RNA unwindase, is associated with malignant transformation, especially by contributing to enhancement of potentiality for carcinogenesis by the deregulation of translation initiation control (12,14,(17)(18)(19)25). In the present study, we demonstrated that rck/p54 plays a role in the maintenance of cell growth probably by modulating the expression of genes involved in cell proliferation at the translation-initiation step, which is in line with the facts that rck/p54 has been verified as an RNA unwindase (14), its homologues have been reported to be associated with translational control (15,24,25) and, in the current study, rck/ p54 interacted with eIF4E.…”

“…Also, high expression of rck/p54 frequently accompanied the c-myc overexpression seen in colon tumor cells; and evidence was obtained by the use of rck/p54-overexpressing SW480 cells, supporting the contribution of rck/p54 to the stabilization of c-myc mRNA and efficiency of c-myc translation (19). However, the enforced expression of rck/p54 in guinea pig fibrosarcoma cell line 104CI resulted in severe growth inhibition and morphological change (20).…”

Knockdown of RCK/p54 expression by RNAi inhibits proliferation of human colorectal cancer cells in vitro and in vivo

“…3 The RCK/p54 protein belonging to the DEAD box protein/RNA helicase family, has various functions such as translation initiation, pre-mRNA splicing and ribosome assembly and it is considered to facilitate the translation of mRNA(s) of genes for cell proliferation and malignant transformation. 4,5 During the process of cell growth and differentiation induced by external stimuli signals, the expression level of rck/p54 gene was upregulated in cell proliferation and downregulated in differentiation. Thus, RCK/p54 contributes to cell growth, but its mechanism inducing carcinogenesis is still unclear.…”