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

Abstract

Colorectal cancer is the third most common cancer in both men and women around the world. Although much progress of the mechanism of colorectal carcinogenesis has been made, the studies centering on the mechanisms of tumorigenesis are much needed to be further exploited. The overexpression of RCK/p54 gene, a member of the DEAD box protein/RNA helicase family, has been found in this malignancy. Roles of RCK in the development of colon cancer, however, are unknown. In this report, we explored whether RCK/p54 plays a role in maintaining the malignant phenotype and functions in the canonical Wnt signaling pathway of colorectal cancer cells harboring an APC mutation. The ectopic overexpression of RCK/p54 gene in colorectal cancer cells by transfection with RCK/p54 cDNA could lead to a significant increase of Tcf transcriptional activity and expression levels of Wnt target genes. By RNAi assay, we also observed that the Tcf transcriptional activity in LoVo-shRNA cells was significantly decreased by approximately 61.3%, while the mRNA and protein expression levels of Wnt target genes were also obviously decreased. Furthermore, the anti-tumour effects and its possible mechanisms of actions in LoVo cells elicited by a decrease in the level of RCK/ p54 by RNAi were examined. Results showed that RCK/p54 downregulation could significantly reduce the viability of LoVo cells, increased cell number of S phase, led to cell apoptosis induction, and inhibited tumor growth in nude mice. Taken together, RCK/ p54 might be a determinant of colorectal cancer proliferation by activating the canonical Wnt pathway and RCK/p54-shRNA might be a potential strategy for colorectal cancer gene therapy.

A novel translational control mechanism involving RNA structures within coding sequences

“…Given the role of DDX6 in PTCH1 mRNA translation, DDX6 overexpression would result in PTCH1 overexpression, a feature typical of pancreatic cancer. Interestingly, DDX6 is overexpressed in several cancers (Nakagawa et al 1999;Hashimoto et al 2001;Miyaji et al 2003;Lin et al 2008;Sen et al 2015;Taniguchi et al 2015), opening the possibility that translational regulation by DDX6 plays an important role in malignant transformations.…”

DEAD box RNA helicase functions in cancer

“…Can both promote and repress translation initiation: associates with P-bodies, ATP hydrolysis allows release from P-bodies and translation initation [32][33][34][35][36][37] 58,65 Developmental roles in many species [57][58][59][60][61][62] Overexpression in several cancers [53][54][55][56] Stimulation of cell cycle progression and proliferation [70][71][72][73][74] Cell cycle progression/proliferation Dhh1p important for recovery from DNA damageinduced G1/S cell cycle arrest in yeast DDX6 required for S-phase progression and cell viability in HeLa and LoVo cells, 73,74 and proliferation in xenograft models 74 (siRNA studies)…”

“…Several studies, with both the human DDX6 and the yeast Dhh1p, have indicated that this protein acts as a positive regulator of cell cycle progression: Dhh1p has been shown to be important for recovery from DNA-damage-dependent G1/S cell cycle arrest, 72 while two separate studies demonstrated that siRNA knockdown of DDX6 resulted in S-phase cell cycle arrest. 73,74 Furthermore, these studies showed that siRNA knockdown of DDX6 resulted in a reduction in cell viability, 73 as well as an increase in cell apoptosis and a reduction in their ability to form tumors in xenograft models. 74 Additionally, overexpression of DDX6 was shown to increase expression of the oncogene c-Myc, consistent with the idea that it would have a positive effect on cell proliferation.…”

“…73,74 Furthermore, these studies showed that siRNA knockdown of DDX6 resulted in a reduction in cell viability, 73 as well as an increase in cell apoptosis and a reduction in their ability to form tumors in xenograft models. 74 Additionally, overexpression of DDX6 was shown to increase expression of the oncogene c-Myc, consistent with the idea that it would have a positive effect on cell proliferation. 55 Taken together, these findings suggest that DDX6 homologs play an important, evolutionarily conserved, positive role in cell cycle progression and proliferation, perhaps through regulating translation of specific mRNAs that play key roles in cell cycle progression.…”

The DEAD box protein Ddx42p modulates the function of ASPP2, a stimulator of apoptosis

“…We show that Ddx42p overrode this effect under various conditions, and Ddx42p knockdown had a proapoptotic effect (Figures 4 and 5). Interestingly, other Ddx proteins, such as Ddx25 (Gutti et al, 2008) and rck/ p54 (Lin et al, 2008b), also promote cell proliferation, and their knockdown induces apoptosis, by yet unknown mechanisms. Ddx42p(1-737), lacking the C-terminal domain that binds to ASPP2, did not interfere with cellular survival, and was incapable of counteracting ASPP2-induced apoptosis.…”