Single v dual knockdowns of the chromatin remodeling ATPase, SNF2L and its isoform, SNF2LT have similar effects on DNA damage but opposite effects on the DNA damage response, cell cycle arrest and apoptosis

Abstract

SNF2L, a chromatin‐remodeling ATPase, is nearly ubiquitously expressed in most malignant and normal cell lines, but our previous studies have shown that only malignant cell lines are sensitive to its knockdown. We have recently observed the presence of a truncated isoform of SNF2L, termed SNF2LT also ubiquitously expressed. Single knockdown of either SNF2L or SNF2LT caused DNA damage, a DNA damage response, cell cycle arrest and apoptosis in a number of highly malignant cell lines including Hela, the MDA‐MB‐468 and ‐231. Both single and dual knockdown similarly caused DNA damage measured by COMET as well as by increased p‐H2AX. However single v dual knockdown had opposite effects on the DNA damage response, cell cycle arrest and apoptosis. Single knockdown of either SNF2L or SNF2LT increased phosphorylated p53 and its downstream genes, GADD45A, 14‐3‐3σ and p21 whereas double knockdown had no effect. Single knockdown caused a G2/M arrest with upregulation of p‐cdc2 whereas double knockdown had no effect. Single knockdown caused profound apoptosis with increased Apaf‐1/caspase 9 whereas double knockdown actually increased cellular proliferation. The results suggest that the ratio of SNF2L/SNF2LT determines how a cancer cell responds to DNA damage, either by initiating a damage response which leads to apoptosis or ignoring the DNA damage and continuing to proliferate. This work was supported by the U.S. Army Breast Cancer Research Program grant W81XWH‐06‐1‐0631.