Induction of mitotic cell death in cancer cells by small interference RNA suppressing the expression of RecQL1 helicase

Abstract

RecQL1 DNA helicase of the human RecQ helicase family participates in DNA repair and recombination pathways during cell-cycle replication. When we examined the effect of RecQL1 suppression on cell growth, we found that RecQL1 silencing by small interference RNA efficiently prevented proliferation of a wide range of cancer cells by inducing mitotic catastrophe and mitotic cell death. In contrast, such mitotic cell death was not seen in the growing normal fibroblasts used as controls, even if RecQL1 expression was fully downregulated. Our results support the hypothesis that endogenous DNA damage that occurs during DNA replication and remains unrepaired in cancer cells due to RecQL1 silencing induces cancer cell-specific mitotic catastrophe through a less-strict checkpoint in cancer cells than in normal cells. We speculate that normal cells are exempt from such mitotic cell death, despite slow growth, because cell-cycle progression is controlled strictly by a strong checkpoint system that detects DNA damage and arrests progression of the cell cycle until DNA damage is repaired completely. These results suggest that RecQL1 helicase is an excellent molecular target for cancer chemotherapy. (Cancer Sci 2008; 99: 71-80)

RECQ1 is required for cellular resistance to replication stress and catalyzes strand exchange on stalled replication fork structures

“…depletion also led to activation of phospho-ATM (ser 1981), a primary DNA damage-response protein, and is consistent with the previous observations. 43 Collectively, our observations indicate possible accumulation of stalled or collapsed replication forks in RECQ1-depleted cells, which would eventually trigger DNA damage signaling.…”

Structure of the human RECQ1 helicase reveals a putative strand-separation pin

“…However, the knockout mice seemed healthy and fertile (12). Two recent reports show that RECQ1 depletion using inhibitory RNA has anticancer effects in cells (14) and xenografts (15); this indicates that RECQ1 may be an important target for cancer therapy.…”

RecQL1 DNA repair helicase: A potential tumor marker and therapeutic target against hepatocellular carcinoma

“…siRNAs (21 bp) targeting RecQL1 mRNA (RecQL1-siRNA) and negative control siRNA (NS-siRNA) were chemically synthesized (Nippon EGT, Toyama, Japan). All siRNA sequences had an overhanging 3'-dTdT at the 3' terminus (14). Sequence-specific gene silencing was confirmed by using cDNA microarray analysis with the Affymetrix GeneChip system (Human Genome U133 Plus 2.0 Array).…”

“…Yet, noncancerous cells and all normal cells tested were unaffected by RecQL1-specific RNA interference (13,14). This unique event was idenitfied as mitotic catastrophe during mitosis of the cell cycle in checkpoint system-deficient cancer cells due to accumulation of DNA damage caused by the absence of the RecQL1 helicase (14). To use this cancer cell-specific killing mechanism for the clinical benefit of anticancer chemotherapy, preliminary trials using model mice inoculated with various human cancer cells have been carried out (15).…”

“…Previously, we found that cancer cells were extremely sensitive to RecQL1 silencing by RNA interference with small interfering RNA (siRNA) and that cell growth was severely inhibited, as if these cancer cells were addicted to highly expressed RecQL1. Yet, noncancerous cells and all normal cells tested were unaffected by RecQL1-specific RNA interference (13,14). This unique event was idenitfied as mitotic catastrophe during mitosis of the cell cycle in checkpoint system-deficient cancer cells due to accumulation of DNA damage caused by the absence of the RecQL1 helicase (14).…”